FLOWER BUD INDUCTION ADVISORY #7 for 2018-2019-2/4/19

Tripti Vashisth, Horticulturist, Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom 

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Induction and flowering status: The Citrus Flowering Monitor System indicates that all Florida citrus areas may have up to two waves of flowers during the normal bloom period. The model projects a February 27th to March 5th first wave full bloom with about 680 to 870 inductive hours depending on location, followed by a second wave around March 14th to 23rd with 818 to 990 inductive hours. Generally, the earliest full bloom dates are for the southern areas of Indian River-Immokalee and Umatilla in the north, but the spread for each wave is only about one week. The second flowering wave is not likely to occur and should be the lighter wave of flowers if it does occur. Remember that mandarin cultivars bloom about 7 to 10 days later than Valencia.

An estimate of when 10% open flowers will occur is February 15th . This is when psyllid sprays should stop and when bees may be moved into or placed near citrus blocks. Each beekeeper should coordinate this timing with their local citrus growers.

FLOWER BUD INDUCTION ADVISORY #6 for 2018-2019-1/14/19

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom 

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Current status: We’ve had good induction, but continuing cold temperature conditions have slowed down flower bud development slightly. Initiation of growth of the first flowering wave (cohort) occurred with about 680 to 850 hours of inductive temperatures from south to north and a second cohort may occur at least in the south where lower inductive hours have occurred. The predicted full bloom date is now March 1 to 3 for most areas except Umatilla which is still late February (24th).

For psyllid control: In groves in Central Florida we are seeing some bud break, maybe 20 % of trees. If you want to get maximum psyllid control you need to apply an adult psyllid spray as soon as possible, before feather flush is present.

FLOWER BUD INDUCTION ADVISORY #5 for 2018-2019-1/7/19

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom 

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Current status: We now have December flower bud growth initiation indicated for north, south and western FAWN sites but not Sebring to Lake Alfred. The first wave or cohort of flower buds initiated growth from 20 December in Umatilla to about Christmas in most other areas with 680 to 840 hours of induction, respectively, from south to north citrus areas. The projected bloom dates for this cohort of flowers are now from February 23 in Umatilla to at or near March 1st for most other areas according to the ‘Citrus Flowering Monitor System’. The weather services predict cooler weather this coming week, which should delay flowering a bit pushing the full bloom date to March 1st as of now.

Since the first flowering wave was initiated with only 680 to 750 hours of induction in the south, a second wave of flowering is very likely in the Indian River and Immokalee areas.

If you didn’t apply a flowering enhancement spray of urea or PO3 at the beginning of initiation of the current flowering wave, it is now too late.I don’t advise applying a spray at the beginning of a second wave since over 800 hours of induction will have been accumulated, sufficient for a good two-part spring bloom.

For spring psyllid control:The small amount of flush associated with a little flowering has passed the egg and nymph stage and adult stage psyllids predominate. Bud break of the new spring flush should be about 15 to 20 January so watch carefully and get an adult spray on before feather flush is present. If you wait until you see flush it is too late and the adults have started laying eggs.

For bee keepers. I think the bloom will be delayed until early March and earliest 10 % open flowers will likely be no sooner than mid-February. I will keep you posted on a weekly basis.

FLOWER BUD INDUCTION ADVISORY #4 for 2018-2019-1/2/19

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

FLOWER BUD INDUCTION ADVISORY #4 for 2018-2019-1/2/19

Tripti Vashisth, Horticulturist Emeritus, Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom 

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Current status: We’ve had fairly cool weather until late December and currently 750 to 950 hours of inductive(hours <68° F) weather have accumulated from southern to northern citrus areas in Florida. Unlike 2017-18 only the most northern area, Umatilla, has initiation of flower bud growth, whereas the initial cohort of flower buds started development at 630 to 815 hours of inductive hours south to north the past year by this time. The full bloom date for Umatilla is Feb 25th with a projected accumulated hours of 838 according to the ‘Citrus Flowering Monitor System’. The Weather Channel predicts 3 more days in the mid-80s, thru Friday. It is likely that most other citrus locations will have initiation of flower bud growth by Saturday if not sooner.

FLOWER BUD INDUCTION ADVISORY #4 for 2017-2018-1/3/18

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

FLOWER BUD INDUCTION ADVISORY #4 for 2018-2019-1/2/19

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom 

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Current Status: We’ve had fairly cool weather until late December and currently 750 to 950 hours of inductive(hours <68° F) weather have accumulated from southern to northern citrus areas in Florida. Unlike 2017-18 only the most northern area, Umatilla, has initiation of flower bud growth, whereas the initial cohort of flower buds started development at 630 to 815 hours of inductive hours south to north the past year by this time. The full bloom date for Umatilla is Feb 25th with a projected accumulated hours of 838 according to the ‘Citrus Flowering Monitor System’. The Weather Channel predicts 3 more days in the mid-80s, thru Friday. It is likely that most other citrus locations will have initiation of flower bud growth by Saturday if not sooner.

The first initiation of growth (first cohort of flowers) was before sufficient induction had occurred to produce a level of flowering for an economic crop except for the northern-most tier of groves. However we now have from 850 to over 1000 hour of induction from south to north plus an additional 130 to 150 hours projected for the following week. There may be enough warmer weather in the southern tier of groves for a second cohort of flower buds to initiate growth after another week, but the Ridge groves probably will be further delayed unless temperatures rise above current predictions. In all cases enough time is occurring between the flower cohorts that they should be visibly distinct on the trees.

I’ll probably provide another update next week if initiation of flower bud growth is indicated by the model for most citrus areas. Important coming dates will be when to spray for adult psyllids before feather flush is present and when the last psyllid spray can be applied before there is danger of harm to bees because of 10 % open flowers. More next week.

FLOWER BUD INDUCTION ADVISORY #3 for 2018-2019-12/21/18

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

FLOWER BUD INDUCTION ADVISORY #3 for 2017-2018-12/20/17

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom 

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Due to the holidays this will be the last flower bud development advisory until after the new year.

 Currently there are 570 to 790 hours of inductive hours (<68° F) from south to north. Over the next seven days an additional 90 to 130 inductive hours should accumulate for totals of 660 to 920 from south to north by December 27th. This would leave South Florida groves slightly below an ideal minimum of 700 hours of inductive temperatures but more northern groves should be above to well above this level by midweek.

The weather center temperature forecast for Immokalee indicates there is likely to be 8 days with daytime highs in the 80s starting about midweek next week. These temperatures are likely to initiate flower bud growth of a first cohort of flowers. At 650 total hours there would likely be a later, second, cohort in the South Florida citrus area. In the mid-Florida area only 4 days in the low 80s are predicted which may not be enough warmer weather to initiate growth. The northern tier of citrus should not respond since cooler weather should continue there

The above scenario is fairly typical and generally looks ok for a good bloom this spring. A problem with HLB affected trees is the amount of off-season, winter bloom, that 1) provides new leaves for continued psyllid population maintenance and 2) takes buds away from the normal productive spring bloom. In the Central area where we are monitoring flush and psyllid populations, there is a mix of off-season conditions from block to block. Many blocks have a scattered flush of flowering buds but many blocks have almost none. There are also blocks in which few flowers are showing, but there are still some vegetative only flush with not more than 4 or 5 flowering shoots on the tree. This is not typical of what we have been seeing the past few years where most of the winter flush is with flowers. I have no idea why things are different except that in citrus, in Florida, things are different every year. These conditions, where flush is occurring, are still taking buds away from the spring flowering.

Everyone have a Happy Holiday season; I’ll be communicating with you in the new year.

FLOWER BUD INDUCTION ADVISORY #2 for 2018-2019-12/11/18

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

FLOWER BUD INDUCTION ADVISORY #2 for 2018-2019-12/11/18

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom. If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Flower bud induction status in 2017-18 for the 2018-2019 crop- In this El Niño winter, cool temperatures are accumulating and rainfall is occurring on the cold fronts as expected. Citrus locations currently have accumulated moderate inductive temperature hours, < 68 degrees F, of 430 to 600 hours from southern to northern areas, respectively. The next 7 days will have low cool temperature accumulation of 100 to 150 hours, south to north. The totals of 530 to 750 hours after this week should be 2/3rd to 3/4th of the total we would like to have for a good economic flower induction level. The following week (10 days out) still looks to be moderately cool with little chance of warm enough temperatures to stimulate bud growth.

Accumulation of cool temperatures and prevention of growth during a fall or winter warm spell is very important for good 2018-19 citrus production. The weather needs to continue to stay cool to prevent early initiation of bud growth, which can occur with daytime temperatures in the mid-80s for 7 to 10 days after accumulated cool inductive temperatures have reached 450 to 500 hours. Fortunately, we have had few continuous days of 80 degree daytime highs and 10 more days of cool weather are predicted by the weather service. Ten cool days will get us to Christmas which is a common date for a warm period to initiate flower bud growth. Continued cool weather until New Year’s day would be even better.

FLOWER BUD INDUCTION ADVISORY #1 for 2018-2019-11/27/18

Presently, the only management tools available to eliminate or reduce the chance of multiple blooms are sufficient drought stress to stop growth or a timely gibberellin (GA) spray near but before the initiation of the first wave of bud growth. Water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality in healthy trees. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a water stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts of cool periods. Sufficiently cool temperatures (< 68 o F maximums) after a cold front rain will usually prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress. (See water stress from HLB and mature fruit retention issues in next paragraph.)

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. In pre-HLB studies, Valencia trees in Central Florida had good flowering and no apparent impact on current crop when irrigation was stopped in early December and resumed in the spring. Unfortunately, with poorer root systems associated with HLB, trees are likely to be under some water stress much of the dry fall, even with normal irrigation practices.  This has led to unwanted early flowering (late December to early February) due to water stress induction of flower buds.  For this reason plus associated preharvest fruit drop, drought stress management of flowering is not a good option for HLB infected trees, essentially all citrus trees in Florida.

That leaves application of a gibberellic acid (GA) spray as an alternative.  GA will reverse induction and knock out a weak first flower initiation, but it has to be applied just before or as the warm period starts.  If induction level is above 600 or 650 hours the spray will not completely stop all of the flowering, but a more concentrated flowering should occur after the second warm period.  Discussion of results from fall GA sprays to reduce off-season winter flowering associated with HLB will be in the next advisory.

Much of what has been stated above has now been incorporated into the ‘Citrus Flowering Monitor Expert System for Florida’.  Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering, respectively. The left side line tracks low temperature accumulation. If the current crop is very heavy, then more cool induction is needed to compensate for the crop load effect. If the current crop is lighter or tree condition better, then fewer total cool temperature hours are needed for an equal level of flowering. The right side line(s) track flower bud initiation and development to full bloom. Recommendations (text below graph) consider the current crop level in assessing when action should be taken to try to reduce or to enhance initiation in the flower bud development process. The system is available on-line: http://disc.ifas.ufl.edu/bloom . The on-line version can be used to evaluate any previous year back to 1998-99 by putting in a March or April date for a FAWN location of your choice in the menu. This program does not work if May through September dates are entered.

 

Additional advisories will follow this preliminary one, roughly bi-weekly, and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.
Additional uses of the ‘Citrus Flowering Monitor System-

1. Timing initial spring psyllid spray – Initial bud growth in the spring is indicated by the ‘Citrus Flowering Monitor System’. Until the leaves in those buds are visible (begin to unfold) there is no available plant material for adult psyllids to lay eggs and begin the cycle of a new population.  An adult psyllid spray at this time is an effective way to disrupt the new psyllid population cycle and this timing provides much longer control.  Bud break usually occurs about 2 to 3 weeks after initiation of bud growth (beginning of differentiation). You can follow this with the ‘Citrus Flowering Monitor System’.  Most growers cannot cover all of their citrus blocks quick enough with their ground equipment to get all blocks covered before feather flush is available for adult psyllids to lay eggs.  An aerial application is more likely to meet the required timing even though canopy coverage is not as efficient.  As this time approaches in December-January  further details will be posted.
2. Appropriate time for bee movement into and out of citrus blocks – The ‘Citrus Flowering Monitor System’ can also be used to judge when 10 % open flowers is likely to occur.  In 2015 and 2016, early and late flowering years, respectively, 54 to 53 days occurred from initiation of bud growth until 10 % open flowers.  Further, when 17 years of flowering data were evaluated it was determined that the weeks until bloom from initiation of bud growth varied by 3 weeks  and mean weekly temperatures for the first 4 weeks determined the length of the flower development period.  Based on the data available, it appears that the time until 10 % open flowers should increase about 7 days per each 5 o F above 60 o F.  We will evaluate these timing predictions for growers to stop spraying more effective, harsher, pesticides for psyllid control and for beekeepers to move bees into citrus this coming spring.  Bee removal timing appears to be about 11 to 15 days after full bloom.  Again we will visit this issue as the model indicates that growth of the first wave of spring flowers has been initiated.

See a previous background introduction for previous important yield responses to cool temperatures: FLOWER BUD INDUCTION ADVISORY #1 for 2012-2013. 

FLOWER BUD INDUCTION ADVISORY #6 for 2017-2018-2/1/18

L. Gene Albrigo, Horticulturist Emeritus, Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom 

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Current status: We have excellent induction, but continuing cold temperature conditions have slowed down flower bud development. One warm event occurred around December 14 to 23 and another generally about January 9 to 19 depending on location. Initiation of growth of the first flowering wave (cohort) occurred with about 630 to 800 hours of inductive temperatures and the second cohort occurred with about 800 to 1400 hours of induction depending on location. The River had only the second timing of flowers initiated according to the Citrus Flowering Monitor System. Overall citrus groves have very good levels of induction and most areas should have at least two waves of slightly overlapping flowering cohorts.

Full bloom dates are now projected to be from February 18 to March 1 and a second from March 13 to 29 depending on the area. In two severely declining Valencia groves near Lake Alfred the first wave is scattered over the trees, and this wave is mostly at the pinhead stage. Valencia groves examined near Ft. Meade were in better condition but still showed a scattering of new flush with pinhead flowers. A few popcorn to open flowers were observed from earlier off-season flower buds.

Off-season flowering: Open flowers and popcorn stages were observed on earlier visits to blocks from Lake Alfred to Frostproof and additional flowers are still showing up. Valencia trees appeared to have more of this than Hamlin, but numbers were low and scattered in all cases. I have not detected a light flush of these growing flower buds this winter that we have seen in previous winters. Perhaps the hurricane, uneven leaf loss and uneven stresses on the trees are contributing to the less even patterns for both off-season and the first spring cohort flowering.

FLOWER BUD INDUCTION ADVISORY #5 for 2017-2018-1/17/18

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

FLOWER BUD INDUCTION ADVISORY #5 for 2017-2018-1/17/18

Gene Albrigo, Horticulturist, Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom 

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week. The Immokalee site is not working properly. Computer technical people are trying to fix the problem.

Current status: We now have December flower bud growth initiation indicated for all sites except the Indian River. The first wave or cohort of flower buds initiated growth about mid-December with 630 to 780 hours of induction, respectively, from south to north citrus areas. Palmdale and perhaps Immokalee initiated growth a little later. The projected bloom dates for this cohort of flowers are now from February 21 to 24, except for March 4 and 16 for Lake Alfred and Palmdale, respectively, according to the Citrus Flowering Monitor System. Again this year, the bloom dates do not follow a sequential date pattern from south to north. There have been an additional 500 inductive hours since the first flowering wave was initiated. The weather service predicts an additional 140 hours of inductive temperatures this coming week, with most areas having 3 days of cooler temperatures, one at or near freezing.

Since the first flowering wave was initiated with only 630 to 750 hours of induction, a second wave of flowering is very likely. A second flower bud cohort is indicated for Arcadia and Mayo (I have an interested grower there). It is likely that all areas will have two cohorts of flowers. It is also likely that the full bloom dates will be a little later than now indicated because of the consistent cool weather through January. The model has probably not caught up yet and the next three cold days should also slow down bud development.

If you didn't apply a flowering enhancement spray of urea or PO3 at the beginning of initiation of the current flowering wave, it is now too late. I don't advise applying a spray at the beginning of a second wave since over 800 hours of induction has been accumulated, sufficient for a good two-part spring bloom. I know some of you sprayed. Tell me if I'm wrong about it probably not helping.

Last week we saw a little bud swell for the coming spring bloom and a small amount of flush and bloom from earlier off-season growth.

For spring psyllid control: The small amount of flush associated with a little flowering had a few nymphs and eggs.

For bee keepers. I think the bloom will be delayed until March and earliest 10 % open flowers will likely be late February. I will keep you posted on a weekly basis.

FLOWER BUD INDUCTION ADVISORY #4 for 2017-2018-1/3/18

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

FLOWER BUD INDUCTION ADVISORY #4 for 2017-2018-1/3/18

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom 

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Current Status: We finally got cool weather in late December, but the initial cohort of flower buds started development at 630 to 815 hours of inductive hours south to north. In general this bud development started around Dec 16 to 18 with Lake Alfred being a little later. The full bloom date is projected to be about February 20 to 23, but the colder weather we are experiencing will probably delay the full bloom date. This week i'll try to determine how much delay will occur and report on the probable delay next week.

The FAWN weather data for Immokalee has not been in-sync with the flowering program website. Hopefully, that problem can be fixed this week.

The first initiation of growth (first cohort of flowers) was before sufficient induction had occurred to produce a level of flowering for an economic crop except for the northern-most tier of groves. However we now have from 850 to over 1000 hour of induction from south to north plus an additional 130 to 150 hours projected for the following week. There may be enough warmer weather in the southern tier of groves for a second cohort of flower buds to initiate growth after another week, but the Ridge groves probably will be further delayed unless temperatures rise above current predictions. In all cases enough time is occurring between the flower cohorts that they should be visibly distinct on the trees.

FLOWER BUD INDUCTION ADVISORY #3 for 2017-2018-12/20/17

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

FLOWER BUD INDUCTION ADVISORY #3 for 2017-2018-12/20/17

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom 

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Current induction status: The cool weather predicted until Christmas is not materializing. We have accumulated minimum levels of induction temperatures, accumulated 570 to 855 hours of cool, inductive temperatures (< 68° F) from south to north, and an additional 90 to `100 hours may accumulate in the next week. However, this week is expected to have highs in the 80s, which may trigger the initiation of development of the first wave of flower buds for the spring bloom.

What can you do?

You should follow the Citrus Flowering Monitor Model on line through this weekend and Christmas day to see if it indicates that a cohort of flower buds has started differentiation. We will have inductive temperatures after Christmas and at worse we will just have two identifiable cohorts of flower buds that extend the bloom period longer than desirable.

If the first cohort of flowers does begin to develop this week, then ideal first spray for psyllids could be early in January (8th to 10th maybe) and 10 % own flowers could be about 55 days after initiation of bud growth. University of Florida will be closed during holidays so watch on-line expert system (it works on holidays) and expect an advisory first week of January.

FLOWER BUD INDUCTION ADVISORY #2 for 2017-2018-12/01/17

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

FLOWER BUD INDUCTION ADVISORY #2 for 2017-2018-12/01/17

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

FLOWER BUD INDUCTION ADVISORY #2 for 2017-2018-12/1/17

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom
If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.
The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week. Additionally estimates of the start of bud break for psyllid spray timing and 5-10 % open flowers to aid in managing psyllid sprays and bee movement for the bloom period will occur with the first initiation of flower bud growth.

Flower bud induction status in 2016-17 for the 2017-2018 crop- In this La Niña winter, with less cool temperature accumulation and rainfall expected, citrus locations currently have accumulated moderate inductive temperature hours, < 68 degrees F, of 300 to 500 hours from southern to northern areas, respectively. The next 7 days will have low cool temperature accumulation of 30 to 70 hours, south to north. The totals of 350 to 550 hours after another week would be 1/3 to ½ of the total we would like to have for a good economic flower induction level.

Accumulation of cool temperatures and prevention of growth during a fall or winter warm spell is very important for good 2018-19 citrus production. The weather needs to continue to stay cool to prevent early initiation of bud growth, which can occur with daytime temperatures in the mid-80s for 7 to 10 days after accumulated cool inductive temperatures have reached 450 to 500 hours. Unfortunately, we have had several days of 80 degree daytime highs and seven more days are predicted by the weather service. Lows are expected to be at near 60. With the low level of induction so far in southern and central areas, we must hope that an initial set of buds do not start growth. It is too bad we cannot apply drought stress to stop initiation of growth at this time. See the first advisory for why this is dangerous with HLB affected trees.

FLOWER BUD INDUCTION ADVISORY #1 for 2017-2018-11/8/17

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. In pre-HLB studies, Valencia trees in Central Florida had good flowering and no apparent impact on current crop when irrigation was stopped in early December and resumed in the spring. Unfortunately, with poorer root systems associated with HLB, trees are likely to be under some water stress much of the dry fall, even with normal irrigation practices.  This has led to unwanted early flowering (late December to early February) due to water stress induction of flower buds.  For this reason plus associated preharvest fruit drop, drought stress management of flowering is not a good option for HLB infected trees, essentially all citrus trees in Florida.

That leaves application of a gibberellic acid (GA) spray as an alternative.  GA will reverse induction and knock out a weak first flower initiation, but it has to be applied just before or as the warm period starts.  If induction level is above 600 or 650 hours the spray will not completely stop all of the flowering, but a more concentrated flowering should occur after the second warm period.  Discussion of results from fall GA sprays to reduce off-season winter flowering associated with HLB will be in the next advisory.

Much of what has been stated above has now been incorporated into the ‘Citrus Flowering Monitor Expert System for Florida’.  Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering, respectively. The left side line tracks low temperature accumulation. If the current crop is very heavy, then more cool induction is needed to compensate for the crop load effect. If the current crop is lighter or tree condition better, then fewer total cool temperature hours are needed for an equal level of flowering. The right side line(s) track flower bud initiation and development to full bloom. Recommendations (text below graph) consider the current crop level in assessing when action should be taken to try to reduce or to enhance initiation in the flower bud development process. The system is available on-line: http://disc.ifas.ufl.edu/bloom . The on-line version can be used to evaluate any previous year back to 1998-99 by putting in a March or April date for a FAWN location of your choice in the menu. This program does not work if May through September dates are entered.

Additional advisories will follow this preliminary one, roughly bi-weekly, and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.
Additional uses of the ‘Citrus Flowering Monitor System-

1. Timing initial spring psyllid spray – Initial bud growth in the spring is indicated by the ‘Citrus Flowering Monitor System’. Until the leaves in those buds are visible (begin to unfold) there is no available plant material for adult psyllids to lay eggs and begin the cycle of a new population.  An adult psyllid spray at this time is an effective way to disrupt the new psyllid population cycle and this timing provides much longer control.  Bud break usually occurs about 2 to 3 weeks after initiation of bud growth (beginning of differentiation). You can follow this with the ‘Citrus Flowering Monitor System’.  Most growers cannot cover all of their citrus blocks quick enough with their ground equipment to get all blocks covered before feather flush is available for adult psyllids to lay eggs.  An aerial application is more likely to meet the required timing even though canopy coverage is not as efficient.  As this time approaches in December-January  further details will be posted.
2. Appropriate time for bee movement into and out of citrus blocks – The ‘Citrus Flowering Monitor System’ can also be used to judge when 10 % open flowers is likely to occur.  In 2015 and 2016, early and late flowering years, respectively, 54 to 53 days occurred from initiation of bud growth until 10 % open flowers.  Further, when 17 years of flowering data were evaluated it was determined that the weeks until bloom from initiation of bud growth varied by 3 weeks  and mean weekly temperatures for the first 4 weeks determined the length of the flower development period.  Based on the data available, it appears that the time until 10 % open flowers should increase about 7 days per each 5 o F above 60 o F.  We will evaluate these timing predictions for growers to stop spraying more effective, harsher, pesticides for psyllid control and for beekeepers to move bees into citrus this coming spring.  Bee removal timing appears to be about 11 to 15 days after full bloom.  Again we will visit this issue as the model indicates that growth of the first wave of spring flowers has been initiated.

See a previous background introduction for previous important yield responses to cool temperatures: FLOWER BUD INDUCTION ADVISORY #1 for 2012-2013.

FLOWER BUD INDUCTION ADVISORY #7a for 2016-2017-2/16/17

This is a note regarding yesterday’s rain and potential for PFD development. Dr. Natalia Peres thinks the rain yesterday should not be much of a problem for development of PFD. At least in the Central Ridge Area the duration was short and the wind dried off the plants very quickly. Fawn sites all seem to have had fairly low rainfall. We saw about .1 to .5 inches in about ½ hour.

FLOWER BUD INDUCTION ADVISORY #7 for 2016-2017-2/15/17

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

FLOWER BUD INDUCTION ADVISORY #6 for 2016-2017-2/15/17

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Induction and flowering status – The Citrus Flowering Monitor System indicates that all Florida citrus areas can have up to three waves of flowers during the normal bloom period. With the winter off-season bloom that could be as many as 4 waves of flowers this year. The model projected a February 8-22 first wave full bloom with about 630 to 800 inductive hours, followed by a second wave around 3 to 16 March with 830 to 1000 inductive hours, and a final wave from March 16 to April 3rd with 1000 to 1200 inductive hours. Generally the earlier dates for each wave are in the southern areas and the higher inductive values are in the northern areas for each flowering wave.

I have only looked at two blocks, one Valencia and one Hamlin, to see how they related to the model. In each block young fruitlets (winter bloom), large popcorn to petal fall (mid-February bloom), small popcorn to large pinhead (predicted early March bloom), and small pinhead (late March projected bloom) were observed. The current February wave was clearly the largest with some fruitlets (winter bloom) and the second regular wave easy to find but in much fewer numbers than the current flowering wave. Some small pinhead flowers were visible in very small numbers. There will be block-to-block variability but the relative number of flowers per tree should follow this trend.

Potential for PFD – We will have flowering overlap until well into or all of March. Natalia Peres (a PFD expert at Balm) says that any white petal surface is susceptible, past pinhead until petal fall. Ovary stigma may be susceptible also. Warmer temperatures with a long leaf wetness period makes for most likely infection. Using current products, a spray following potential infection probably needs to be applied within one day after unfavorable conditions. A local production manager I talked with today hasn’t seen much if any PFD symptoms on flower petals in their groves up to now. He was concerned about potential rain today and Friday but the weather channel suggests that rain is more likely to occur in the north central region with less chance of rain Friday.

FLOWER BUD INDUCTION ADVISORY #5 for 2016-2017-1/17/17

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

FLOWER BUD INDUCTION ADVISORY #6 for 2016-2017-1/17/17

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Weather has been cool with good inductive temperature conditions. All citrus areas have also had sufficient warm periods for one to two flower bud initiation events to occur in December. One warm event occurred around December 11 to 21 and another December 28-30 or as late as January 1st in Immokalee. Initiation of growth of the first flowering wave (cohort) occurred with about 635 to 800 hours of inductive temperatures and the second cohort (all areas except the Indian River and Sebring) occurred with about 835 to 1000 hours of induction. The River and Sebring probably also has a second wave of flowers initiated, but the Citrus Flowering Monitor System did not report one. Currently there are 930 to 1220 inductive hours from south to north. The next 9 days should add 80 to 150 more hours south to north. Citrus groves have very good levels of induction, all areas should have at least two waves of overlapping flowering and some could have three leading to a very prolonged flowering period.

Full bloom dates are now projected to be in mid-February (10-20) and early March (7 to 11). All popcorn or larger flowers now on the trees are off-season flowering from stress induction during the fall, mostly due to HLB decline creating water stress.

Off-season flowering: I have had two reports about off-season flowering from the lower central ridge area. One reported observing light to heavy flowering in almost all blocks. More declined trees usually had the heaviest flowering. These blocks received two or three irrigations per week in the fall. In another operation several blocks were observed that had lower amounts of off-season bloom and these blocks were irrigated 4 to 5 times per week. In our monitored blocks trees in relatively good condition have lower but easily observed flowering at this time. One block in poorer condition has considerably more off-season flowering than the other blocks we are monitoring. Normal bud break for the spring flower cohorts has started. Some blocks already have leaf feathers and pinhead flowers. This may be a good time for an effective adult psyllid spray, but last week was better for more advanced blocks.

FLOWER BUD INDUCTION ADVISORY #4 for 2016-2017-1/3/17

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

FLOWER BUD INDUCTION ADVISORY #3 for 2016-2017-1/3/17
This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

IIf you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week.

Current status: We now have December flower bud growth initiation which started from December 11 to 21 after 630 to 800 hours of induction, respectively, from south to north citrus areas. The projected bloom dates for this cohort of flowers are from February 13 to 27 according to the Citrus Flowering Monitor System. The bloom dates do not follow a sequential date pattern from south to north. There have been an additional 100 to 200 inductive hours from south to north since the first flowering wave was initiated. The weather service predicts an additional 90 to 140 hours of inductive temperatures this coming week, with most areas having 10 to 12 days of cooler temperatures.
Since the first flowering wave was initiated with only 650 hours of induction from Central to South Florida, a second wave of flowering is very likely. If a second flower bud cohort is going to be initiated soon, it is likely to be right away since we are just finishing a warm period. Watch the on-line monitoring system over the next week to see if a second wave is shown for your area. If a flowering wave doesn’t start within a week then the predicted 11 or 12 cool days should delay any second wave of flowering until after mid-January, not until we have another warm period.

If you didn’t apply a flowering enhancement spray of urea or PO3 at the beginning of initiation of the current flowering wave, it is now too late. I don’t advise applying a spray at the beginning of a second wave since over 800 hours of induction will have accumulated, sufficient for a good two-part spring bloom.

Off-season bloom: If you are going to have some winter bloom, buds should have pushed by now and are probably in some stage of visible flowering. I have seen one poor condition grove with some flowers. Please email me if you have significant winter flowering on reasonably healthy (full canopied) trees. Hopefully, if you were on a daily, if needed, irrigation regime you are not seeing much off-season flowers.

Spring sprays for psyllids: At least two entomologists think that a spray just at spring budbreak might be a best time to get maximum adult psyllid control at the beginning of spring growth and minimize production of a new population on the spring flush. Over the last two years it appears that bud break may be as early as 56-57 days before full bloom. If this is correct then bud break may start any time. Check your trees! My crew will be looking at several blocks today and tomorrow. I’ll post a new advisory if we see any significant bud break or bud swelling that shortly will lead to bud break.

FLOWER BUD INDUCTION ADVISORY #2 for 2016-2017-12/20/16

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

FLOWER BUD INDUCTION ADVISORY #4 for 2016-2017-12/20/16
This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

IIf you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

We are 2/3rd of the way through December and now have 580 to 800 hours of inductive hours south to north. The Citrus Flowering Monitor System does not indicate the beginning of bud growth in any of the Florida citrus areas. Bud growth of outermost shoot buds can easily occur now that 600 to 800 hours of induction have occurred. As growers have kept their trees well-watered, trying to minimize preharvest fruit drop from HLB, the adequate soil moisture will allow bud growth as soon as sufficient warm days occur.

In the southern area, Immokalee and Clewiston, warm days, 83 to 85° F. are predicted for 8 of the next 10 days. Bud growth may start in this area for a first flowering wave. Since drought stress from stopping irrigation is ill advised with HLB, growers may want to consider a PO3 or urea spray before Christmas if they can afford it.

Urea or PO3 sprays for flower enhancement will probably be beneficial, particularly for this southern area with low inductive hours and if drought stress cannot be established. Growers can consider applying from 53 to 60 lbs of foliar urea/acre or a PO3 product at 3 pints to 2 quarts per acre depending on which product is used (60 % P (3pts) or if 26 % P (2 qts)). The chosen material should be applied in 30 to 100 gal/acre in order to get good coverage. These products apparently increase the stress level and enhance the amount of flowering induced by the cool temperatures.

There are some winter flower buds in some groves but mostly if not in good condition due to the HLB disease. The flush and flowers are at the expense of buds that normally would have been flower buds next spring. Of 15 blocks we are monitoring, only one has buds developing.

The La Niña situation. The meteorologists still indicate that a weak La Niña is under-way. This increases the chances of a freeze, but so far the jet stream over the southern-most US has been moving from southwest to northeast, avoiding pulling colder air toward us. If this continues until mid-January our chance of a freeze is greatly reduced. We should still get cooler inductive temperatures in January and early February, which will lead to at least two waves of flowering this year if some bud growth starts over the next 10 days.

FLOWER BUD INDUCTION ADVISORY #3 for 2016-2017-11/29/16

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

FLOWER BUD INDUCTION ADVISORY #3 for 2016-2017-11/29/16
This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Current induction status: We have now gone through November with continuing moderate temperatures accumulating 420 to 600 hours of cool, inductive temperatures (< 68° F) from south to north, whereas only 130 to 330 inductive hours were accumulated by this time last year. Most growers have kept their trees well-watered, trying to minimize preharvest fruit drop from HLB; even so little bud swell appears to have occurred at least in Central Florida. The next 10 days look to be fairly warm with little cool temperature induction expected. If you have trees in good condition with little fruit drop maybe they can withstand some drought stress the next 7-10 days in order to prevent bud break (see previous two advisories). The 5 days following after that are supposed to cool down. We need the trees to get to just over 700 hrs as a minimum for an economic flowering level. Therefore, preventing bud break under these projected warmer temperatures is very desirable.

What can you do? You can reduce irrigation to create mild drought stress in order to stop bud break now, but this will probably increase your preharvest fruit drop. If you have harvested your Hamlin blocks, you can consider water stressing these. Even if you haven’t harvested yet this is still an option if you haven’t seen severe preharvest fruit drop in a given block, but many Hamlin blocks were showing severe preharvest fruit drop in early to mid-September.

At only 400 accumulated hours of induction, the induction level is too low in Central and South Florida to increase flowering to the economically desirable level by using a flowering enhancement spray of urea or PO3 at this time. With another 100 to 150 hours of induction these southern groves could respond well to sprays of either material. North Florida groves might have enough induction now, but they will be under cooler weather and may not need flower enhancing sprays anyway.

Many growers are complaining about small fruit size this year. Remember that we had a late bloom which partly accounts for the small fruit size. Of course HLB is also partly responsible. These two factors also may result in higher acidity levels on any given date compared to a year ago.

FLOWER BUD INDUCTION ADVISORY #2 for 2016-2017-11/15/16

Flower Bud Induction Overview and Advisory
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus

L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

FLOWER BUD INDUCTION ADVISORY #2 for 2016-2017-11/15/16
This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom
If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week. In January we plan to have estimates of the start of vegetative flush and 5-10 % open flowers to aid in managing psyllid sprays for the bloom period, a CRDF supported effort.

Flower bud induction status 2016-17 for 2017-2018 crop- In this weak La Niña winter, with less cool temperature accumulation and rainfall, citrus locations currently have accumulated moderate inductive temperature hours, < 68 degrees F, of 200 to 330 hours from southern to northern areas, respectively. The next 7 days will have moderate cool temperature accumulation of 90 to 125 hours, south to north. The totals of 290 to 450 hours after another week could be 200 to 270 hours ahead of November 23rd last year. Check same dates at your location for last year and this year.

Accumulation of cool temperatures and prevention of growth during a fall or winter warm spell is very important for good 2017-18 citrus production. The weather needs to continue to stay cool to prevent early initiation of bud growth, which can occur with daytime temperatures in the mid-80s for 7 to 10 days after accumulated cool inductive temperatures have reached 450 to 500 hours. This year these levels of induction should be reached by early December for most Florida citrus areas.

Normal healthy trees could have their induction boosted by applying some drought stress. Unfortunately, with vulnerable root systems associated with HLB you shouldn’t risk heavier preharvest fruit drop of the current crop by using water stress to prevent unwanted early vegetative growth while enhancing induction of flowers (see previous advisory (background) on use of drought stress). In fact HLB infected trees the four previous years have had winter flowering due to water stress induced flowering from infrequent irrigation and poor root water uptake in the typically dry fall. I am advocating daily, lower volume irrigations to minimize fall water stress, but if warmer temperatures occur in December this may lead to a winter flush of growth.

FLOWER BUD INDUCTION ADVISORY #1 for 2016-2017-11/1/16

TFlower Bud Induction Overview and Advisory 
NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS 
The following information has been developed as part of the Decision Information System for Citrus

L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

FLOWER BUD INDUCTION ADVISORY #1 for 2016-2017-10/31/16
This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom
If you are not familiar with the website and flower bud induction in citrus you should read the overview section below the current status paragraphs.

In the on-line version you can shift from one FAWN weather site to another without back tracking. All citrus area FAWN sites are in the menu.  The total accumulated hours is now listed as is the forecast (projected) hours to be accumulated the following week.  By January we hope to have estimates of the number of days before full bloom for the start of vegetative flush and 5-10 % open flowers to aid in managing psyllid sprays for the bloom period. This latter information is a CRDF supported effort.

Flowering related to the current 2016 -17 Crop Estimate– In spite of a reportedly strong El Niño winter, cool flower bud inductive temperatures did not start until January.  The later than normal inductive period was also largely responsible for the later final bloom in April. Even so, last spring’s flowering had two strong flowering periods in March and April and should have resulted in a good crop considering the HLB disease condition of the trees.  Unfortunately heavy spring rains followed off-season and regular blooms that carried over PFD fungal inoculum to the final flowering cohort resulted in severe losses to PFD in many blocks, particularly of navels and Valencia. The current estimate is for 70 million boxes of round oranges, which would have been closer to last year’s crop without the PFD losses.

Flower bud induction status 2016-17 for 2017-2018 crop- This is probably going to be a weak La Niña ENSO winter (45 % chance) with higher than average cool temperature accumulation and lower rainfall.  Currently, citrus locations have accumulated low inductive temperatures, < 68 degrees F, of only 65 to 147 hours from southern to northern areas, respectively. The next 7 days will have low cool temperature accumulation with less than 40 to 75 hours, south to north. This is slightly more hours than last year, which had very low accumulation of low temperatures until January. Accumulation of cool temperatures and prevention of growth during a winter warm spell is very important for good 2017-18 citrus production.  The weather needs to cool down soon and follow a better pattern of cool temperature accumulation than last year.

During the previous 4 years with chronic HLB Florida citrus trees have had early to late winter flowering due to water stress induced flowering because of poor root systems and infrequent irrigation in the fall.  
Several IFAS faculty, including me, are advocating daily, lower volume, irrigations to minimize fall water stress.  Fewer off-season flowers results in more buds available for normal winter cool temperature induction and spring season flowering.  Reduced off-season flowering also reduces off-season leaves for psyllid population development.

Overview of flower bud induction in Florida – Citrus flower bud induction starts in the fall and usually is completed by early January. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F, 20 o C). Periods of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm winter-springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida probably will be a weak ENSO-El Niña year, above average temperatures and lower than average rainfall. Under these conditions, enough hours of low temperatures < 68 degrees F. will usually accumulate to induce an economic level of flower buds, but intermediate warm periods during the winter lead to multiple flower cohorts and a very prolonged bloom.  Other conditions that can interfere with good flower bud induction include: 1) exceptionally high previous crop or 2) excessive leaf loss from hurricanes, freezes or other causes (canker, HLB) where tree recovery is not complete. Excessive leaf loss leads to low carbohydrate levels in developing buds which reduces their ability to become flower buds and/or to set. None of the adverse environmental conditions appear to be in play for the coming season’s flower bud induction but a freeze is still possible. The biggest concern will be reduced available carbohydrates in weaker trees because of HLB.   

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 800-850 hours < 68 degrees F. If the crop load is light and trees are healthy, sufficient flower bud induction may occur after 700-750 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures from 80 to 85 degrees F., can trigger growth (bud swelling) if a minimum total hours of low temperatures have accumulated (350-450 hours < 68 degrees F). Later in the winter when the accumulated cool temperature induction hours are higher, fewer days and lower daytime highs (5-7 days, 75 degrees F.) are required in a warm period to stimulate growth of buds. Weather information relative to Florida citrus flower bud development for the current and several previous years (back to 1998) can be obtained and evaluated with the Citrus Flowering Monitor System using data from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. An 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt for the next week. Find this information at: http://www.nws.noaa.gov/mdl/forecast/text/state/FL.MRF.htm. This is an easy way to see if a warm period, which could trigger flower bud growth, is predicted for your specific area in Florida.

Some flower buds will be induced in the range of 350 to 450 accumulated hrs < 68 degrees F. Warm events after these levels of induction are met result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well irrigated. The first situation results in multiple cohorts of flower buds developing to different bloom dates. The second condition leads to low flowering-fruit set and excessive early spring vegetative growth. During the years from 1963 to 2003, multiple blooms occurred in over half of the years. Historically, the time period in which an early warm period (7-12 day) can lead to an initial low number of buds growing and flowering is roughly mid-November to mid-December. Then after more cool temperatures additional flower buds are induced and a later warm period starts their growth and repeats of this temperature cycle result in multiple blooms, usually two to three, but all in the mid-February to early April normal spring flowering period.

Presently, the only management tools available to eliminate or reduce the chance of multiple blooms are sufficient drought stress to stop growth or a timely gibberellin (GA) spray near but before the initiation of the first wave of bud growth. Water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality in healthy trees. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a water stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts of cool periods. Sufficiently cool temperatures (< 68 o F maximums) after a cold front rain will usually prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress. (See water stress from HLB and mature fruit retention issues in next paragraph.)

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. In pre-HLB studies, Valencia trees in Central Florida had good flowering and no apparent impact on current crop when irrigation was stopped in early December and resumed in the spring. Unfortunately, with poorer root systems associated with HLB, trees are likely to be under some water stress much of the dry fall, even with normal irrigation practices.  This has led to unwanted early flowering (late Dec. to Feb.) due to water stress induction of flower buds.  For this reason plus associated preharvest fruit drop, drought stress management of flowering is not a good option for HLB infected trees, essentially all citrus trees in Florida.

That leaves application of a GA spray as an alternative.  GA will reverse induction and knock out a weak first flower initiation, but it has to be applied just before or as the warm period starts.  If induction level is above 600 or 650 hours the spray will not completely stop all of the flowering, but a more concentrated flowering should occur after the second warm period.

Much of what has been stated above has now been incorporated into a ‘Citrus Flowering Monitor Expert System for Florida’.  Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering, respectively. The left side line tracks low temperature accumulation. If the current crop is very heavy, then more cool induction is needed to compensate for the crop load effect. If the current crop is lighter or tree condition better, then fewer total cool temperature hours are needed for an equal level of flowering. The right side line(s) track flower bud initiation and development to full bloom. Recommendations (text below graph) consider the current crop level in assessing when action should be taken to try to reduce or to enhance initiation in the flower bud development process. The system is available on-line: http://disc.ifas.ufl.edu/bloom . The on-line version can be used to evaluate any previous year back to 1998-99 by putting in a March or April date for a FAWN location of your choice in the menu. 
Additional advisories will follow this preliminary one, roughly bi-weekly, and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

See a previous background introduction for previous important yield responses to cool temperatures: FLOWER BUD INDUCTION ADVISORY #1 for 2012-2013. 

FLOWER BUD INDUCTION ADVISORY #1 for 2015-2016-11/5/15

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom
If you are not familiar with the website and flower bud induction in citrus you should read the overview section below the current status paragraph.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week. Unfortunately next week’s cool temperature accumulation estimate still need some work to make it work properly. By January we hope to have estimates of the start of vegetative flush and 5-10 % open flowers to aid in managing psyllid sprays for the bloom period, CRDF supported effort.

Flowering related to the current 2015 -16 Crop Estimate– Last spring’s flowering was more consistent and should have resulted in a better crop than estimated. Spring stress was less so reduced tree numbers and poorer tree health must be responsible for the reduced estimate if in fact we will have a crop of only 80 million boxes of sweet oranges. There was a flowering cohort toward the end of February after nearly 850 hours of inductive temperature induction (< 68 degrees F) followed by a second from 1000 hours of induction.

Flower bud induction status 2015-16 for 2016-2017 crop- This is supposed to be a very strong ENSO winter with more cool temperature accumulation and rainfall. Currently however, citrus locations have accumulated low inductive temperatures, < 68 degrees F, of only 30 to 130 hours from southern to northern areas, respectively. The next 7 days will have low cool temperature accumulation with less than 50 hours, south to north. This is nearly 200 hours behind last year. Accumulation of cool temperatures and prevention of growth during a winter warm spell is very important for good 2016-17 citrus production. The weather needs to cool down soon and follow an expected El Niño pattern.
Normal healthy trees could have their induction boosted by applying some drought stress. Unfortunately, with vulnerable root systems associated with HLB you shouldn’t risk heavier preharvest fruit drop of the current crop by using water stress to prevent unwanted early vegetative growth and enhance induction of flowers (see later section on use of drought stress). In fact the previous years with HLB have had late winter flowering due to drought induced flowering from infrequent irrigation in the fall. I am advocating daily, lower volume irrigations to minimize fall water stress.

Overview of flower bud induction in Florida – Citrus flower bud induction starts in the fall and usually is completed by early January. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F, 19 0C). Periods of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm winter-springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be an ENSO-El Niño year, below average temperatures and above average rainfall. Under these conditions, enough hours of low temperatures below 68 degrees F. will usually accumulate to induce an economic level of flower buds, but intermediate warm periods during the winter lead to multiple flower cohorts and a very prolonged bloom. Other conditions that can interfere with good flower bud induction include: 1) exceptionally high previous crop or 2) excessive leaf loss from hurricanes, freezes or other causes (canker, HLB) where tree recovery is not complete. Excessive leaf loss leads to low carbohydrate levels in developing buds which reduces their ability to become flower buds and/or to set. None of the adverse environmental conditions appear to be in play for the coming season’s flower bud induction as freezes are less likely in an El Niño year. The biggest concern will be reduced available carbohydrates because of HLB.

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 800-850 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction may occur after 700-750 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures from 80 to 85 degrees F., can trigger growth (bud swelling) if a minimum total hours of low temperatures have accumulated (350-450 hours below 68 degrees F). Later in the winter when the accumulated cool temperature induction hours are higher, fewer days and lower daytime highs (75 degrees F.) are required in a warm period to stimulate growth of buds. Weather information relative to Florida citrus flower bud development for the current and several previous years (back to 1998) can be obtained and evaluated with the Citrus Flowering Monitor System using data from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. An 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt for the next week. Find this information at: http://www.nws.noaa.gov/mdl/forecast/text/state/FL.MRF.htm. This is an easy way to see if a warm period, which could trigger flower bud growth, is predicted for your specific area in Florida.

Some flower buds will be induced in the range of 350 to 450 accumulated hrs < 68 degrees F. Warm events after these levels of induction are met result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well irrigated. The first situation results in multiple cohorts of flower buds developing to different bloom dates. The second condition leads to low flowering-fruit set and excessive early spring vegetative growth. During the years from 1963 to 2003, multiple blooms occurred in over half of the years. Historically, the time period in which an early warm period (7-12 day) can lead to an initial low number of buds growing and flowering is roughly mid-November to mid-December. Then after more cool temperatures additional flower buds are induced and a later warm period starts their growth and repeats of this temperature cycle result in multiple blooms.

Presently, the only management tools available to eliminate or reduce the chance of multiple blooms are sufficient drought stress to stop growth or a timely gibberellin (GA) spray at the initiation of first wave bud growth. Water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality in healthy trees. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts for cool periods. Sufficiently cool temperatures (< 70 degrees F maximums) after a cold front rain will usually prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. In pre-HLB studies, Valencia trees in Central Florida had good flowering and no apparent impact on current crop when irrigation was stopped in early December and resumed in the spring. Unfortunately, with poorer root systems associated with HLB, trees are likely to be under some water stress much of the dry fall, even with normal irrigation practices. This has led to unwanted early flowering (late Dec. to Feb.) due to drought stress. For this reason plus associated preharvest fruit drop, drought stress management of flowering is not a good option for HLB infected trees, essentially all citrus trees in Florida.

That leaves application of a GA spray as an alternative. GA will reverse induction and knock out a weak first flower initiation, but it has to be applied just before or as the warm period starts. If induction level is above 600 or 650 hours the spray will not completely stop all of the flowering, but a more concentrated flowering should occur after the second warm period.

Much of what has been stated above has now been incorporated into a ‘Citrus Flowering Monitor Expert System for Florida’. Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering, respectively. If the current crop is very heavy, then more cool induction is needed to compensate for the crop load effect. If the current crop is lighter or tree condition better, then fewer total cool temperature hours are needed for an equal level of flowering. Recommendations (bottom text) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process. The system is available on-line: http://disc.ifas.ufl.edu/bloom. The on-line version can be fully appreciated by putting in a March or April date for any previous year, back to 1999, for a location of your choice in the menu.

Additional advisories will follow this preliminary one, roughly bi-weekly, and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

See a previous background introduction for previous important yield responses to cool temperatures: FLOWER BUD INDUCTION ADVISORY #1 for 2012-2013.

FLOWER BUD INDUCTION ADVISORY #2 for 2015-2016-11/24/15

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom. If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week. By January we hope to have estimates of the start of vegetative flush and 5-10 % open flowers to aid in managing psyllid sprays for the bloom period, a CRDF supported effort.

Flower bud induction status 2015-16 for 2016-2017 crop- In spite of this being a strong ENSO winter, supposedly with more cool temperature accumulation and rainfall, citrus locations currently have accumulated few inductive temperature hours, < 68 degrees F, only 50 to 215 hours from southern to northern areas, respectively. The next 7 days will have low cool temperature accumulation with 50 to 80 hours, south to north. This is still about 200 hours behind last year. Some southern area anomalies include very low accumulated hours in Immokalee and Clewiston, while the Indian River FAWN site is moderately low, but Kenansville has more hours than Avalon. The accuracy of these sites will be checked.
Accumulation of cool temperatures and prevention of growth during a fall or winter warm spell is very important for good 2016-17 citrus production. The weather needs to cool down soon and follow an expected El Niño pattern.

Normal healthy trees could have their induction boosted by applying some drought stress. Unfortunately, with vulnerable root systems associated with HLB you shouldn’t risk heavier preharvest fruit drop of the current crop by using water stress to prevent unwanted early vegetative growth and enhance induction of flowers (see previous advisory (background) on use of drought stress). In fact the three previous years with HLB have had late winter flowering due to drought induced flowering from infrequent irrigation in the fall. I am advocating daily, lower volume irrigations to minimize fall water stress, but with warmer temperatures this may lead to a fall flush of growth. We can’t seem to win in this HLB environment.

EMERGENCY FLOWER BUD INDUCTION ADVISORY #3 for 2015-2016-12/1/15

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week.

We have now gone through November with continued mild temperatures, only 130 to 330 inductive hours south to north. As growers have kept their trees well-watered, trying to minimize preharvest fruit drop from HLB, the warm weather plus adequate soil moisture has stimulated a strong fall flush in many groves. There are some flowers in this fall flush indicating that even though well-watered, some water stress has occurred in the trees due to HLB disease. The flush and flowers are at the expense of buds that normally would have been flower buds next spring. There are limited options of what to do since it looks like December will also be warmer than normal.

First to the El Niño situation. The meteorologists still indicate that a strong El Niño is on the way, but it has been delayed, at least in the Southeastern US. The jet stream over the southern-most US has been moving from southwest to slightly northeast pulling warmer air toward us. The weather people believe the strong El Niño will be later in the winter. This may allow us to get cooler inductive temperatures in January and February, but continued warm temperatures in December will stimulate additional flush.

What can you do? You can reduce irrigation to create mild drought stress in order to stop fall growth. You probably don’t want to do this since preharvest fruit drop will be increased. If you have harvested your Hamlin blocks, you can consider this. Even if you haven’t harvested yet this is still an option if you haven’t seen severe preharvest fruit drop in a given block. But if your trees have already produced a strong fall flush consider the next option.

If you have a strong fall flush you have few spring-summer flush buds left to flower in the spring. But the new flush has potential for flowering next spring. It requires about 8 weeks for a flush to mature so that the new buds are receptive to flower bud inductive conditions, cool temperatures or drought. If the flush started in mid-November it will be mature in mid-January. We may have cool weather through February, which could be supplemented by drought stress to mid-March in order to induce adequate flowering by late spring. This plays out as follows: new flush matures, mid-November to mid-January, flush is induced to have flower buds, mid-January to mid-March, flowering in mid-April. This scenario will require keeping the trees dry in the late winter-early spring so that they do not flush again before mid-March. Valencia trees could be under full irrigation by mid-March to help reduce some of the preharvest drop. This protocol would be improved by a flowering enhancement spray of urea or PO3 just before growth is resumed. I will provide more details later.
Valencia fruit, as well as Hamlin, will mature earlier this year because the fall warm temperatures have accelerated acidity decline causing ratio to increase early. There may be some benefit of warmer winter temperatures increasing soluble solids production of Valencia fruit, but the effect will probably be small compared to the acidity decline.
If I think of any other ways to recoup spring flowering, I’ll provide those ideas in a future advisory.

EMERGENCY FLOWER BUD INDUCTION ADVISORY #4 for 2015-2016-12/15/15

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week.

We have now gone through half of December with continued mild temperatures, only 200 to 500 inductive hours south to north. As growers have kept their trees well-watered, trying to minimize preharvest fruit drop from HLB, the warm weather plus adequate soil moisture has stimulated a strong fall flush in most groves. There are some flowers in this fall flush indicating that even though well-watered, some water stress has occurred in the trees due to the HLB disease. The flush and flowers are at the expense of buds that normally would have been flower buds next spring. There are limited options of what to do and according to the weather predictions the next 10 days of December will also be warmer than normal.

First to the El Niño situation. The meteorologists still indicate that a strong El Niño is under-way, but it has been delayed, at least in the Southeastern US, no explanation. The jet stream over the southern-most US has been moving from southwest to slightly northeast pulling warmer air toward us. This has continued the past two weeks. We may still get cooler inductive temperatures in January and February, but continued warm temperatures through December will probably stimulate additional flush.

What can you do? See the December 1st advisory about why you may not want to apply water stress to stop growth. In addition, the horse is already out of the barn in most groves regarding a strong fall flush.

If you have a strong fall flush you have fewer spring-summer flush buds left to flower in the spring. But the new flush has potential for flowering next spring. It requires about 8 weeks for a flush to mature so that the new buds are receptive to flower bud inductive conditions, cool temperatures or drought. If the flush started in mid-November it should be mature in mid-January. We may have cool weather through February, which could be supplemented by drought stress to mid-March in order to induce adequate flowering by late spring. This plays out as follows: new flush matures from mid-November to mid-January, flush is induced to have flower buds, mid-January to mid-March, flowering in mid-April. This scenario will require keeping the trees dry in the late winter-early spring so that they do not flush again before mid-March. Valencia trees could be under full irrigation by mid-March to help reduce some of the preharvest drop. This protocol would be improved by a flowering enhancement spray of urea or PO3 just before growth is resumed.

A flower enhancement spray of urea or PO3 probably should not be considered before mid to late February, later than normal. This is definitely the case if you have a strong fall flush. If you do not have a fall flush, then the critical time to apply either material will be in January after we have 550 or 600 hours of induction but before we revert to warm weather, day time highs in the 80s. I hope we have some cool weather in January.

Urea or PO3 sprays in February for flower enhancement will probably be beneficial, particularly for southern areas and if drought stress was not established. Growers can consider applying from 53 to 60 lbs of foliar urea/acre or a PO3 product at 3 pints to 2 quarts per acre depending on which product is used (60 % P (3pts) or if 26 % P (2 qts)). The chosen material should be applied in 30 to 100 gal/acre in order to get good coverage. These products apparently increase the stress level and enhance the amount of flowering induced by the cool temperatures.

Again if little flush apply either product in January after more induction and before 7-10 day warm period starts. If strong fall flush, wait until mid-February and apply before warm period starts. Use water stress to stop growth if late January or early to mid-February has warm period.

EMERGENCY FLOWER BUD INDUCTION ADVISORY #5 for 2015-2016-12/23/15

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week.
Projections for December flower bud induction are still very poor with continued mild temperatures until January. There are only 260 to 570 inductive hours from south to north. The next 10 days do not look any better. Umatilla will accumulate only 25 more hours in December if the weather predictions are correct. That accumulation will not occur until the last two days of December.

The El Niño situation. The meteorologists still indicate that a strong El Niño is under-way, but it has been delayed, at least in the Southeastern US, no explanation. The jet stream over the southern-most US has been moving from southwest to slightly northeast pulling warmer air toward us. This has continued the past two weeks, is currently the same and predicted temperatures for the next 10 days suggests there will be no major change in the jet stream. The continued warm temperatures through December may stimulate additional flush.

If you have a strong fall flush you have fewer spring-summer flush buds left to flower in the spring. But the new flush has potential for flowering next spring. This flush should be mature by mid-January and the new buds receptive to flower bud inductive conditions, cool temperatures or drought. If cooler weather kicks in and goes through February, which could be supplemented by drought stress to mid-March, we would have adequate flowering by late spring. This will require keeping the trees dry in the late winter-early spring if warm temperatures occur so that they do not flush again before mid-March. Applying drought stress to Hamlins should cause no problems but Valencia trees will have accelerated preharvest drop if they require prolonged water stress. This protocol would be improved by a flowering enhancement spray of urea or PO3 before growth is resumed. The amounts required and timing were reviewed in the last advisory (#4, 12/15/15). Even if you did not have a heavy fall flush, a flower enhancement spray of urea or PO3 probably should not be considered before late January to mid-February, later than normal. The critical time to apply either material will be after we have 550 or 600 hours of induction, another 200 to 300 hours in all areas from Lake Alfred and to the south. The application has to be before we revert to warm weather, day time highs in the 80s. Of course all we have had is warm weather so far. If warm weather continues in January, I would consider instituting drought stress conditions.

What to do about Valencia trees this year is not an easy decision. Do you drought stress to get flowers for next year’s crop and sacrifice some of this crop? Hopefully cool temperatures will start in January and you can avoid having to make this decision.

FLOWER BUD INDUCTION ADVISORY #5 for 2015-2016-1/4/16

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

IIf you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week.

The hoped for cooler temperatures for flower bud induction have finally arrived and appear to be favorable at least until mid-January. Currently there are 300 to 600 inductive hours from south to north. The next 7 days should add 80 to over 100 more hours south to north, and the following week appears to be similar. Citrus groves from Sebring north should have at least minimum hours by mid-January, while south Florida will still have a weak level of induction. See below for discussion of strong and weak fall flush conditions regarding flower induction levels and use of enhancement sprays.

The El Niño situation. The meteorologists have stated a strong El Niño is under-way, but it had not reached the Southeastern US until now. The jet stream over the southern-most US has moved slightly north to south, which may be contributing to cooler temperatures in Florida. Hopefully this late arrival of the El Nino will also lead to cooler temperatures being sustained longer into the New Year.

Tree flush condition and options for flowering enhancement. If you have a strong fall flush you have fewer spring-summer flush buds left to flower in the spring. But the new flush has potential for flowering next spring. This flush should be mature by mid-January and the new buds receptive to flower bud inductive conditions, cool temperatures or drought. This flush is probably finishing maturation and beginning to accumulate inductive temperatures now. Still this late flush may need supplemental induction from drought stress to mid-March in order to have adequate flowering by late spring. This will require keeping the trees dry in the late winter-early spring if warm temperatures occur so that they do not flush again before mid-March. Applying drought stress to Hamlins should cause no problems but Valencia trees will have accelerated preharvest drop if they require prolonged water stress. This protocol would be improved by a flowering enhancement spray of urea or PO3 before growth is resumed. The amounts required and timing were reviewed in advisory #4 (12/15/15).

Even if you did not have a heavy fall flush, a flower enhancement spray of urea or PO3 should not be considered before mid-January or 1 week before warm weather is predicted. The critical time to apply either material will be after we have 550 or 600 hours of induction. This requirement should be met in all areas by mid-January. The application has to be before we revert to warm weather, day time highs in the 80s. The weather predictions are favorable past mid-January and should be followed closely over the next few weeks.

Be prepared to spray light fall flush groves around mid-January and to make decisions about heavy fall flush groves as warm weather is predicted, 10 day warning on major weather channels.

What to do about Valencia trees this year is not an easy decision if you have a heavy fall flush. If no heavy fall flush, it appears that an enhancement spray can be applied mid- to late January, depending on how long cool temperatures continue in January. But is you have a heavy fall flush, you need 600 to 800 hours of cool temperatures starting in January. Obtaining this many hours below 68 o F is not likely, but do you drought stress as cool temperatures end in order to get higher flowering levels for next year’s crop and sacrifice some of this crop? Hopefully cool temperatures will continue through January and well into February so you can avoid having to make this decision. Generally, I don’t think growers will sacrifice some of this year’s crop for flowers for next year’s crop.

FLOWER BUD INDUCTION ADVISORY #5 for 2015-2016-1/19/16

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week.

Many trees may have a light flowering flush at popcorn or open flower stage. I see the equivalent of 5 % of a normal bloom, light but problematic if rain leads to PFD on this bloom. Again this year this very early bloom is due to fall water stress induction related to the HLB disease.

The El Niño situation. The expected strong El Niño has finally reached the Southeastern US. The cooler temperatures are expected to last at least until January 31st. Hopefully the El Nino associated cooler temperatures will be sustained well into February. Be sure to evaluate the various options if cool temperatures are not sustained beyond January.

Induction status for last year’s spring and summer flush – Thanks to cooler temperatures starting in early January bud inductive hours are currently from 580 to 950 hours from south to north. The next 7 days should add 140 to over 155 more hours south to north, and the following week appears to be similar. Citrus groves from Sebring north have at least minimum hours, while south Florida has a weak level of induction. All areas should be in the acceptable low range or higher by the end of January.

Fall flush condition and options for flowering enhancement. Even though a strong fall flush resulted in fewer spring-summer flush buds left to flower this spring, this new flush now has potential for flowering next spring. From the time the fall flush matured sufficiently to be induced (about January 5th), 240 to 280 inductive hours have accumulated from south to north in the citrus region of Florida. By February 1st, this could reach 530 to 575 hours. Optimum flowering would require at least another 200 hours of cool temperatures (<68° F) or 2 or 3 weeks of drought stress in February.

The first option to gain this supplemental induction is to follow the weather and see if February will continue this cool temperature inductive trend. If not, drought stress can be initiated before the warm weather starts and continued for 2 or 3 weeks in February. Applying drought stress to Hamlins should cause no problems but Valencia trees will have accelerated preharvest drop if they require prolonged water stress. For Valencia trees the alternative is to apply a flower enhancing spray of urea or PO3 before growth is resumed. The amounts required and timing were reviewed in advisory #4 (12/15/15).

Even if you did not have a heavy fall flush, a flower enhancement spray of urea or PO3 should not be considered before late January or 1 week before warm weather is predicted. The critical time to apply either material will be after we have 550 or 600 hours of induction. This requirement should be met in all areas the last 10 days of January. The application has to be before we revert to warm weather, expected day time highs in the 80s for 5 or more days. Follow the 10 day weather forecasts closely over the next two weeks.

Be prepared to spray groves with all flush conditions around late January unless you make a decision to drought stress heavy fall flush groves as warm weather is predicted.

What to do about Valencia trees this year is not an easy decision, but weather conditions are much more favorable than two weeks ago. If weather warms up in early February, reasonable flowering should occur if tree flowering is boosted with a flower enhancing spray the end of January. If cool weather continues into February, spring flowering could approach normal levels.

FLOWER BUD INDUCTION ADVISORY #5 for 2015-2016-1/26/16

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week.

Induction status – Thanks to cooler temperatures starting in early January bud inductive hours are currently from 700 to 1100 hours from south to north. The next 7 days should add 100 to 140 more hours south to north. Citrus groves will have 810 to 1200 hours, enough hours for normal induction of last year’s spring and summer flush.

Fall flush status. For trees with a strong fall flush, this flush will have 500 to 600 hours of inductive temperatures by February 1st. This flush need another 175 to 250 hours of induction after that. Unfortunately, the first 4 days of February are predicted to be at or near 80° F for highs. It is recommended that all harvested cultivars with a strong fall flush be put in drought stress by Monday. Stop irrigation until cool temperatures resume. If temperature highs return to below 75 and lower after that, the drought stress can be relieved.

For Valencia trees with a strong fall flush the best option is to apply a urea or PO3 spray to enhance flowering before Tuesday or Wednesday next week at the latest.

FLOWER BUD INDUCTION ADVISORY #5 for 2015-2016-2/1/16

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week. Now that initiation of flower bud growth has started in some areas (see Umatilla) this information is also listed at the top of the graph.

Induction status – Through this week bud inductive hours will be 900 to 1300 hours from south to north. The next 7 days will contribute 60 to 130 more hours south to north. Citrus groves will have enough cool temperature induction for normal induction of last year’s spring and summer flush. There is a possibility that flower bud growth will start this week as 4 days of high 70s to low 80s are predicted from today through Thursday. Trees in the Umatilla area have already started flower bud growth according to the ‘Citrus Flowering Monitor System Model’. Full bloom is projected to be March 30th for this area.

Fall flush status. For trees with a strong fall flush, the fall flush will have 575 to 670 hours of inductive temperatures by February 6th. This flush will need another 80 to 175 hours of induction from north to south after this week in order to reach 750 hours of induction. Unfortunately, the next 4 days may trigger initiation of growth of all flushes. I was hoping for dry weather last week so that we could go through this week with the trees in drought stress. I guess that is why I’m not a weatherman. There are another 9 or 10 days of cool weather predicted after this week’s warm period. If you have a small enough area of early-mid season cultivars that are already harvested, you might consider a urea or PO3 spray in the next two days to try and boost flowering if you had a heavy fall flush.

For Valencia trees with a strong fall flush hopefully you applied a urea or PO3 spray to enhance flowering late last week or are doing so early this week.

FLOWER BUD INDUCTION ADVISORY #5 for 2015-2016-2/8/16

And initial intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

See below for first attempt to predict bloom related psyllid spray dates based on model and initial phenology data from 2014-15.

Induction status – The ‘Citrus Flowering Monitoring System’ predicts that the first spring wave of flowering will be in full bloom March 29 to 31 from Sebring north, but the model has not yet predicted a first wave of flowering for South Florida nor the Indian River. Initiation of this flowering wave from Sebring north was January 23rd (Umatilla) to January 27th (Central Ridge) with 840 to 1150 hours of cool inductive temperatures. This should be enough hours so that last year’s normal spring and summer flushes can have sufficient flowering levels.

From forecasted cool temperatures, the total flower bud inductive hours will be 1050 to 1490 hours from south to north Florida after the next 7 days. There should be another 7 days of mostly inductive temperatures after that according to 15 day weather predictions. This should lead to a second flowering wave in April, primarily on fall flush.

Fall flush status - For trees with significant fall flush, this flush was probably about 300 to 350 hours short of good induction when the first wave of flowers were induced. So, I think there will be light flowering in this flush south of the northern areas of citrus, from Avalon north. The current cool temperatures should induce more buds which should initiate growth perhaps in another two weeks for a mid-April flowering.

Flowering time, bee activity and spray scheduling – Although we only have one year of data, it looks like 5 to 10 % full bloom will be reached about 21 to 27 days before full bloom. Therefore, we might expect the cut-off date for the effective psyllid sprays may be about March 3 to 9. Bud break of vegetative shoots should be 7 to 13 days before that. Therefore, a spray window of only one to 2 weeks may exist between covering the new vegetative growth with an effective psyllid spray and the need to shift to bee-friendly materials.

Caution – This is our first look at the flowering time / spray schedule situation and you should use it as a guide to see how accurately it predicts these stages of vegetative and reproductive growth in relationship to the 5 to 10 % open flower stage when spray chemicals need to be changed. Also, it assumes the full bloom date estimate is correct. The model has been accurate most years to plus or minus 7 days, but does not adjust well for delays from colder than normal temperatures near bloom and may not account for possible HLB effects on spring bloom. Use these estimates as guidelines to prepare, but watch your trees closely for final decisions on spray timing.

FLOWER BUD INDUCTION ADVISORY #5 for 2015-2016-2/10/16

And initial intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Look before you leap: A few weeks ago I described a light flowering, 5 to 10 % of a normal bloom in January and typical of a fall drought stress induced bloom typical of HLB affected trees. I didn’t think much more of it, and we finally saw a normal spring flowering wave predicted by the flowering model for late March. I sent a crew out to set up flower development sites and received a report of wide-spread flowering. This is in pinhead to full bloom stage and varies from another 5 to 10 % of a full bloom to many trees with a general bloom of at least half of a normal spring bloom. Groves vary as do trees within groves in the amount of flowering currently present. The amount of flowering on a given tree did not always relate to the apparent tree health in this tree to tree variability.

The time period since the cool weather started, January 1st, is 40 days. This is probably less than the minimum days required for flowers to develop after initiation of growth at the average max/min temperatures that occurred for this time period at Lake Alfred, 70/53. Therefore I am fairly certain that this is another drought stress induced flowering that started to grow no later than the end of December, when we had about 400 hours of cool temperature flower induction. At Lake Alfred the average max/min temperatures in December were 82/65. Therefore temperatures in December were favorable for drought stress or vegetative growth if groves were irrigated, and most were but associated poor root systems of HLB affected trees still leads to drought stress at those temperature. Since January 1st, growth would be slow but possible during daytime highs of 70. There was almost no rainfall in December at Lake Alfred, but frequent rains started by January 8th. The lack of rains in December would have contributed to drought stress and the frequent rains after January 1st would have favored continued flower bud development.

On some trees this second fall induced stress bloom has taken significant numbers of buds from the later normal bloom period. On some trees you can see small fruit from the first stress bloom wave, another but small reduction in buds for a later bloom. There should still be a late March bloom in all citrus districts, but it will probably vary inversely to the amount of current flowering on the trees.

This current flowering might be attractive to bees if air temperatures were warmer. Daytime highs are not predicted to reach mid-70s or higher until February 18th and early morning lows are supposed to be below 60 until then also. More favorable grove conditions for bees of new citrus flowers and warmer temperatures should occur with the late March bloom.

FLOWER BUD INDUCTION ADVISORY #5 for 2015-2016-2/23/16

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu.  Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week. Now that initiation of flower bud growth has started in some areas (see Umatilla) this information is also listed at the top of each graph.

Induction status – We now have two waves of flowers developing according to the ‘Citrus Flowering Monitor System Model’.  Full bloom for the first wave is projected to be March 25th to April 1st with the earlier dates in the southern districts. Growth of these flower buds was initiated after 800 to 1100 hours of induction, south to north. Growth of the second wave was initiated February 2nd to 11th after 980 to 1200 hours of induction.  This second wave has not been predicted yet for Balm, Avalon or Umatilla northern, cooler locations) by the model.

A report from southern Polk and Highlands Counties said they have a lot of pinhead flowers.  Another report indicates mostly pinhead flowers also. I don’t know if the weather will hold the flowers back until the end of March.  Remember that cooler weather near bloom does stall flower development. 

However, in the next 15 days, those weather people are predicting 2 to 3 days in the 80s, followed by 3 or 4 days of cool daytime temperatures, but then followed 9 or 10 days in the high 70s to low 80s.  Nighttime temperatures will be in the 40s to mid-50s.  I advise you to keep a close eye on flower development so you can get a last, more effective psyllid spray on before you reach 5 to 10 % open flowers.  In Advisory 10, we predicted that the cut-off spray date might be March 3-9 depending on area of the state.  We’re monitoring 8 blocks and so far we have only pinhead flowers. We’ll update what we see, but it may be too late so watch your own blocks.  Remember there is a table to record data on flowering stage that was distributed a year ago.  I have attached this information and form at the bottom of this advisory.

Fall flush status - For trees with a strong fall flush, the second flowering wave had 650 to 740 hours of inductive temperatures and more northern areas will have 800 or more.  This should be enough hours to induce flowering in the fall flush if it was mature enough to be receptive to cool temperature induction by January 5th.

PFD - In spite of early stress blooms, a grower in Highlands and Hardee Counties did not see much PFD.  I didn’t see much if any in 7 or 8 blocks in Polk County.  Perhaps neither of us looked in the worst groves.  Please report to Megan Dewdney (mmdewdney@ufl.edu) if you did see evidence in the January-early February stress bloom of PFD.
Determining Percent Bloom in Florida Citrus Groves

In Florida, citrus bloom varies by year, typically occurring in 2-3 waves of flowering anytime from February through the end of March. When citrus trees are in bloom, many pesticide labels prohibit application due to potential for negative effects on pollinators, particularly managed honeybees. The expected time of greatest foraging in blooming citrus by bees is from 10-90% open bloom for each cultivar. For Florida citrus growers, this would be the period when use of pesticides, which restrict application during bloom, should cease.

There are a number of factors that can influence when citrus trees will bloom including weather patterns, cultivar, expected yield, tree age, and soil type. Tree stress, such as drought stressprobably occur in HLB affected trees and cause trees to produce off-season bloom.  Not only does such off-season bloom fail to produce harvestable fruit, but the bloom tends to have much lower levels of nectar for pollinators. Because off-season bloom can occur weeks to months in advance of “true bloom”, it is important to have a good understanding of when “true bloom” is likely to occur and focus efforts on monitoring bloom abundance at that particular time.

The Citrus Flowering Monitor (http://disc.ifas.ufl.edu/bloom/) is an online tool for Florida citrus growers that predicts when peak bloom is likely to occur in a growing area based on factors such as weather, cultivar, and growing conditions. When a prediction of peak bloom is obtained, growers should begin documenting bloom abundance in their groves at least 4 weeks   prior to peak bloom to determine when the grove has reached 10% bloom and application of bloom prohibited pesticide applications should cease. The following sampling protocol can be used to determine the percent bloom in a citrus grove.

With the exception of grove edges which receive more sunlight than the rest of the grove and are likely to bloom earlier, bloom is typically uniform throughout a grove and thus sampling to estimate bloom abundance can be performed with relatively minimal effort.  Sampling bloom abundance is performed using a 2’x2’ frame (made of PVC pipe or other material of choice) placed at the surface of the canopy of the tree and the total number of open blooms counted within the frame is divided by the total number of potential blooms (pinhead to open blooms). Dividing the frame using string to create four quadrants may facilitate the ease of counting the numerous bloom stages that may be present. Counts should be taken at least at ½ of tree height, and counting from a pickup bed will speed up the process.

A total of 12 frame counts of bloom can be made to estimate bloom abundance in a cultivar. Choose two row middles (spaced approximately 1/3 and 2/3 across the block) to make counts.  For each of the 2 row middles sampled, select 3 sampling locations evenly spaced down the row.  At each stop, make frame counts of bloom abundance on two trees (one tree on the left side of the row middle [tree 1] and one tree on the right side of the row middle [tree 2]).

Table 1 is provided as a template for record keeping purposes for documenting the stage of bloom present.  When 10% of the developing bloom (pinhead stage to open flowers) have reached the open flower stage, then application of bloom restricted pesticides should cease.  Conversely, when the majority of developing bloom have reached petal fall (developing fruitlets predominate) and less than 10% of developing fruit stages consist of bloom with white petals, then pesticide applications can resume. In the event that questions should arise regarding application of pesticides during bloom, growers should retain documentation of bloom sampling used to time pesticide applications based on percent bloom.

Table 1. Data recording sheet for estimating percent bloom in a citrus grove.

	Row 1		Row 2
Stop	# flowers & new fruitlets	# open blooms	# flowers & new fruitlets	# open blooms
1
2
3
4
5
6
	Sum =	Sum =	Sum =	Sum =
	Column A	Column B	Column C	Column D

Sum Column A___________________ + Column C _____________________ =  (E)__________________

Sum Column B ___________________ + Column D_____________________ = (F)___________________

Percent bloom = total # open bloom (F) ÷ Total # developing buds (E)

(F)___________________ ÷ (E)_________________ = ___________________Percent bloom

FLOWER BUD INDUCTION ADVISORY #5 for 2015-2016-3/10/16

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

The on-line version has been updated so that you can shift from one FAWN weather site to another without back tracking. More FAWN sites have been added to the menu. Another added feature is that the total accumulated hours is now listed as is the projected hours to be accumulated the following week. Now that initiation of flower bud growth has started in some areas (see Umatilla) this information is also listed at the top of each graph.

Induction status – The two waves of regular bloom flowers continue to develop and are easy to see in Central Florida groves. Most of the scattered early stress bloom should now be past petal fall. According to the ‘Citrus Flowering Monitor System Model’ the projected full bloom dates for the first wave are projected to be March 24th to March 31st, one day earlier, with the earliest date in the Indian River District. Growth of these flower buds was initiated after 800 to 1100 hours of induction, south to north. Growth of the second wave was initiated February 2nd to 11th after 980 to 1200 hours of induction. This second wave still has not been predicted yet for Balm, Avalon or Umatilla northern, cooler locations) by the model. They probably will not show a second bloom in the model, but will have a second flowering wave if there was any significant amount of fall flush.

Of eight blocks we are monitoring, all but one is still at the pinhead to popcorn stage. Only one has open flowers (2.5 %). This is slower bloom development than predicted as of 2/23/16, but temperatures were cooler than predicted. This resulted in our not reaching the 5 % open flowers by yesterday. However, in the next two weeks, the weather predictions are for the highs to be 77 to 92 with nighttime temperatures from the mid-50s to mid-60s. Flower development should be much more rapid with these temperatures. Five to 10 % open flowers should come soon, but we will likely have newly open flowers until 10-15 April. South Florida groves will likely be ahead of this schedule. If you see any difference in bloom development in your area than these predictions please let me know. I wouldn’t mind hearing if they are correct also.

Remember for critical bee pollination of mandarins, the small flowered cultivars will have their peak bloom for each flowering wave 7 to 10 days later than those stated above for processing sweet oranges cultivars. You can see this by changing the cultivar in the on-line model.

FLOWER BUD INDUCTION ADVISORY #1 for 2014-2015-11/5/15

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom. If you are not familiar with the website and flower bud induction in citrus you should read the overview section below the current status paragraph.

Flowering related to the current 2014 -15 Crop – There was a light but consistent bloom centered in January that must have been a water stress bloom initiated in November due to the effect of HLB on root systems. There was a flowering cohort toward the end of February after nearly 900 hours of inductive temperature induction (< 68 degrees F). Remnants of the January bloom overlapped with the beginning of this cohort. A second regular cohort occurred toward the end of March after more than 1200 hours of induction had occurred, resulting in an extended bloom. The January bloom with associated rains may have been the inoculum source for extensive PFD seen in the regular bloom since little PFD has been seen the past few years. In spite of PFD, NASS predicted a larger crop for this harvest season than the previous year supporting the effect of the high induction levels.

Flower bud induction status 2014-15 - his is supposed to be a weak ENSO winter with more cool temperature accumulation and rainfall than last year. Currently, citrus locations have accumulated low, inductive temperatures, < 68 degrees F, of nearly 300 to 400 hours from southern to northern areas, respectively. The next 7 days will be intermediate for cool temperature accumulation with about 70 to 110 hours, south to north. Continued accumulation of cool temperatures and prevention of growth during a winter warm spell is very important for good 2015-16 citrus production. Another 4+ weeks with 80 to 100 hours/week od inductive temperatures will give the trees a low economic level of flowering.
Normal healthy trees could have their induction boosted by applying some drought stress. Unfortunately, with vulnerable root systems associated with HLB you shouldn’t risk heavier preharvest fruit drop of the current crop by using water stress to prevent unwanted early vegetative growth and enhance induction of flowers (see later section on use of drought stress). Trees will be very vulnerable to growth stimulation by a warm period after they accumulate 300-400 hours of cool temps if soil moisture is adequate. Keep track of induction hours in your area and watch for projected warm periods from the weather services. The next advisory will be after December 2nd unless a warm period is predicted or other unusual events occur. Remember drought stress adds to flower bud induction, but it also increases drop of the current crop.

Overview of flower bud induction in Florida – Citrus flower bud induction starts in the fall and usually is completed by early January. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F, 19 0C). Periods of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm winter-springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be a weak ENSO year, below average temperatures and higher than average rainfall. Under these conditions, enough hours of low temperatures below 68 degrees F. will usually accumulate to induce an economic level of flower buds, but intermediate warm periods during the winter can lead to multiple flower cohorts and a very prolonged bloom. Other conditions that can interfere with good flower bud induction include: 1) exceptionally high previous crop or 2) excessive leaf loss from hurricanes, freezes or other causes (canker, HLB). Excessive leaf loss leads to low carbohydrate levels in developing buds which reduces their ability to become flower buds. None of the adverse climatic conditions appear to be in play for the coming season’s flower bud induction. The biggest concern may be reduced available carbohydrates because of HLB.

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 800 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction may occur after 700-750 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures from 80 to 85 degrees F., can trigger growth (bud swelling) if a minimum total hours of low temperatures have accumulated (300-400 hours below 68 degrees F). Later in the winter when the accumulated cool temperature induction hours are higher, fewer days and lower daytime highs (75 degrees F.) are required in a warm period to stimulate growth of buds. Weather information relative to Florida citrus flower bud development for the current and several previous years (back to 1998) can be obtained from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. An 7 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt for the next week. Find this information at: http://www.nws.noaa.gov/mdl/forecast/text/state/FL.MRF.htm. This is an easy way to see if a warm period, which could trigger flower bud growth, is predicted for your specific area in Florida.

Some flower buds will be induced in the range of 300 to 450 accumulated hours < 68 degrees F. Warm events after these levels of induction result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well irrigated. The first situation results in multiple cohorts of flower buds developing to different bloom dates. The second condition leads to low flowering-fruit set and excessive early spring vegetative growth. During the years from 1963 to 2003, multiple blooms occurred in over half of the years. Historically, the time period in which an early warm period (7-12 day) can lead to an initial low number of buds growing and flowering is roughly mid-November to early-December. Then after more cool temperatures additional flower buds are induced and a later warm period starts their growth. This pattern can repeat itself, often leading to 3 blooms in the same season.

Presently, the only management tools available to eliminate or reduce the chance of multiple blooms are sufficient drought stress to stop growth or a timely gibberellin (GA) spray just before initiation of the first wave of flower bud growth. Water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or fruit quality in healthy trees. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts for cool periods. Sufficiently cool temperatures after a cold front rain will usually prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. In recent studies, Valencia trees in Central Florida have had good flowering and no apparent impact on current crop when irrigation was stopped in early December and resumed in the spring. Now in the face of HLB and related preharvest drop, it may not be a good idea to allow trees to become drought stressed.

Application of a GA spray is an alternative. GA will reverse induction and knock out a weak first flower initiation, but it has to be applied just before or as the warm period starts. If induction level is above 600 hours the spray will not completely stop all of the flowering, but a more concentrated flowering should occur after the second warm period. The GA application will work better if the warm period occurs after only 400 to 450 hours of cool temperatures.
Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus’. Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering, respectively. If the current crop is very heavy, then more cool induction is needed to compensate for the crop load effect. If the current crop is lighter or tree condition better, then fewer total cool temperature hours are needed for an equal level of flowering. Recommendations (bottom text) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process. The recommended actions are for healthy trees and may poorly apply to HLB affected trees, today’s typical Florida citrus tree. The system is available on-line: http://disc.ifas.ufl.edu/bloom. The on-line version is in black and white and does not list the accumulated hours of cool temperatures or the predicted bloom date.

You must interpret those from the intersections with the graph axis. An improved on-line version is being developed this season.

Additional advisories will follow this preliminary one, roughly bi-weekly, and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

See a previous background introduction for previous important yield responses to cool temperatures: FLOWER BUD INDUCTION ADVISORY #1 for 2012-2013.

FLOWER BUD INDUCTION ADVISORY #2 for 2014-2015-12/03/14

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
Tripti Vashisth, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

Current Status: The projection is for a weak ENSO winter with slightly above average cool temperature accumulation. The accumulated hours below the threshold for induction, <68° F, through December 1 were <530 to 730 from southern to northern citrus areas. Another 35 to 75 hours are predicted for the next week. The minimum hours in southern areas will be about 250 hours less than the desired 850 after next week. So far, the Indian River has a few more inductive hours than Immokalee this year.

In order to improve the induction level beyond a minimum, trees need to remain at rest at least through Christmas. Cool temperature accumulation or drought stress can increase induction levels. Three more weeks of cool temperature induction may add another 250-300 hours, which would bring the East Coast growing areas to near 850 hours, an acceptable level of flowering for an economic crop. A level of 900 hours or more should be reached in most growing areas north of Sebring in three more weeks if cooler temperatures persist.

In Central to southern growing areas daytime high temperatures are projected to be in the low-80 degree range for the next 5 days, If temperatures are higher than this or high temperatures continue for more days, shoot terminal buds may initiate growth at the current induction levels. Induction levels are now high enough that a warm period will easily initiate bud growth in the 1st and 2nd terminal buds. At a minimum level of bud induction when bud growth starts, the flower buds will have few flowers and more leaves.

Because of preharvest fruit drop associated with drought stress, an alternative is to enhance flower bud induction with a stress inducing spray of urea or PO3 at the beginning of a winter warm period after more than 600 hours of cool temperatures accumulate.

This can boost flowering levels as if additional cool temperatures had occurred. A flower bud induction enhancement spray of urea or a phosphorous acid product sprayed during the early part of the warm period probably will be effective. Growers can consider applying either 53 to 60 lbs of foliar urea/acre or a PO3 product at 3 pints to 2 quarts per acre depending on which product is used (60 % P (3pts) or if 26 % P (2 qts)). The chosen material should be applied in 80 to 125 gal of water early in a warm period. These products apparently increase the stress level and enhance the amount of flowering induced by the cool temperatures. We have not tested these sprays on HLB affected trees, but these trees, if not severely declined, may also respond. A downside of this is the additional cost with productions costs already very high due to HLB related treatments.

If cool temperatures continue for 3 weeks, flower enhancing sprays may not be needed even in southern areas. Trees with a weak root systems (all HLB trees) may express water stress which would enhance flowering. On the other hand weak root systems from HLB could also be a problem. Poor production of cytokinins by roots in the spring minimizes final flower development. Unfortunately our knowledge of how HLB alters tree physiology is very limited and we can only guess at much of the response.

Moderate drought stress increases cold hardiness on healthy trees, also increases flower bud induction and prevents bud growth in warm weather. Flowers are visible on some limbs in trees indicating that at least some parts of trees are stressed. This is not as heavy as last year’s January bloom. The HLB associated drought stress is likely to increase preharvest fruit drop now, particularly in Hamlins and early mandarins with HLB, as long as rain frequency is not steady.

Don’t forget that winter freezes occur most often between Christmas and 15 January. However, an El Nino year is less likely to have freeze events. Watch the weather for warm periods and freeze potential.

FLOWER BUD INDUCTION ADVISORY #3 for 2014-2015-12/17/14

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

Current Status: Within 4 days cool temperature induction will have reached 820 to 950 hours below 68° F for southern to central citrus producing regions in Florida.

With the higher induction levels that are now present, the buds will begin to grow if daytime high temperatures reach 80°F for just a few continuous days. Such conditions are predicted for South Florida citrus areas. The Indian River and Central Florida will be border-line for growth initiation temperatures.

Since cool temperatures have reached these levels, flower enhancing sprays may not be needed, but one of the chemical sales companies correctly pointed out that enhancing flowering intensity will reduce the possibility of multiple blooms. The advantage of this is to shorten the time when harsher psyllid sprays can’t be applied and reduce the chance of another PFD event this season and the number of sprays that are needed if PFD does occur.

See the last advisory for flower enhancement spray information. If you choose to apply either urea and/or PO3 you should do so immediately. The recommendations are for one or the other. We have not data on combining the two products at some reduced rate.

FLOWER BUD INDUCTION ADVISORY #1 for 2013-2014-11/21/13

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom. If you are not familiar with the website and flower bud induction in citrus you should read the overview section below the current status paragraph.

Flowering related to the current 2013 -14 Crop – Last spring we had 3 flowering waves. The predicted dates of full bloom were late January after 600 hrs of induction for the first bloom, for the second it was in mid-February after about 800 hours of induction and the last was for March 1st after 1000 hours. The first wave actually occurred about mid-February and was very light. Early flowering cultivars, through Hamlin oranges, had their second wave of flowers about March 1st with the third in Mid-March. However, Valencias did not bloom until April whereas normally they bloom within a week of Hamlin trees of similar condition. There was a warm period in early February that pushed flower development and helped early cultivars to complete flower development as the rest of February and early March had alternating cool and warmer spells, particularly for night time minimums. Later cultivars apparently could not develop fast enough under these temperature conditions and about March 22nd a very cool period occurred that lasted until April 1st. This completely stopped flower development and Valencias did not flower until April, nearly a month after Hamlins. We can expect some additional delay in Valencia maturity after the Hamlin harvest. The spring was relatively cool and all cultivars appear to be late in maturing, but some of that may be attributed to HLB, which reduces soluble solids accumulation and maintains higher acidity levels.

Flower bud induction status 2013-14 - This is supposed to be an ENSO-Neutral winter with average cool temperature accumulation and rainfall. But until now, accumulated inductive hours have been fairly low. Currently, citrus locations have accumulated low temperatures, < 68 degrees F, of less than 170 to 380 hours from southern to northern areas, respectively. The next 7 days will be intermediate for cool temperature accumulation with about 56 hours in the Indian River and 100 hours in Umatilla. Continued accumulation of cool temperatures and prevention of growth during a winter warm spell is very important for good 2014-15 citrus production. Unfortunately, you may not want to risk heavier preharvest fruit drop of the current crop by using water stress to prevent unwanted early vegetative growth and initiation of flower bud development (see later section on use of drought stress). An alternative is to spray a gibberellin just as flower bud growth initiation starts, which will reverse the induction already stimulated (see below). Trees will be very vulnerable to growth stimulation by a warm period after they accumulate 300-400 hours of cool temps. Keep track of induction hours in your area and watch for projected warm periods from the weather services. The next advisory will be after December 2nd. Remember drought stress adds to flower bud induction, just avoid excessive drought to maintain adequate condition of the current crop.

Overview of flower bud induction in Florida – Citrus flower bud induction starts in the fall and usually is completed by early January. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F, 19 0C). Periods of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm winter-springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be an ENSO-Neutral year, average temperatures and rainfall. Under these conditions, enough hours of low temperatures below 68 degrees F. will usually accumulate to induce an economic level of flower buds, but intermediate warm periods during the winter can lead to multiple flower cohorts and a very prolonged bloom. Other conditions that can interfere with good flower bud induction include: 1) exceptionally high previous crop or 2) excessive leaf loss from hurricanes, freezes or other causes (canker) when tree recovery was not complete. Excessive leaf loss leads to low carbohydrate levels in developing buds which reduces their ability to become flower buds. Generally, none of these adverse conditions appear to be in play for the coming season’s flower bud induction. The biggest concern may be reduced available carbohydrates because of HLB.

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 800 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction may occur after 700-750 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures from 80 to 85 degrees F., can trigger growth (bud swelling) if a minimum total hours of low temperatures have accumulated (300-400 hours below 68 degrees F). Later in the winter when the accumulated cool temperature induction hours are higher, fewer days and lower daytime highs (75 degrees F.) are required in a warm period to stimulate growth of buds. Weather information relative to Florida citrus flower bud development for the current and several previous years (back to 1998) can be obtained from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. An 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt for the next week. Find this information at: http://www.nws.noaa.gov/mdl/forecast/text/state/FL.MRF.htm. This is an easy way to see if a warm period, which could trigger flower bud growth, is predicted for your specific area in Florida.

Some flower buds will be induced in the range of 300 to 450 accumulated hrs < 68 degrees F. Warm events after these levels of induction are met result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well irrigated. The first situation results in multiple cohorts of flower buds developing to different bloom dates. The second condition leads to low flowering-fruit set and excessive early spring vegetative growth. During the years from 1963 to 2003, multiple blooms occurred in over half of the years. Historically, the time period in which an early warm period (7-12 day) can lead to an initial low number of buds growing and flowering is roughly mid-November to early-December. Then after more cool temperatures additional flower buds are induced and a later warm period starts their growth and repeats of this temperature cycle result in multiple blooms.

Presently, the only management tools available to eliminate or reduce the chance of multiple blooms are sufficient drought stress to stop growth or a timely gibberellin (GA) spray at the initiation of first wave bud growth. Water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts for cool periods. Sufficiently cool temperatures after a cold front rain will usually prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. In recent studies, Valencia trees in Central Florida have had good flowering and no apparent impact on current crop when irrigation was stopped in early December and resumed in the spring. Now in the face of HLB and related preharvest drop, it may not be a good idea to allow trees to become drought stressed.

That leaves application of a GA spray as an alternative. GA will reverse induction and knock out a weak first flower initiation, but it has to be applied just before or as the warm period starts. If induction level is above 600 or 650 hours the spray will not completely stop all of the flowering, but a more concentrated flowering should occur from the second warm period.

Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus’. Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering, respectively. If the current crop is very heavy, then more cool induction is needed to compensate for the crop load effect. If the current crop is lighter or tree condition better, then fewer total cool temperature hours are needed for an equal level of flowering. Recommendations (bottom text) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process. The system is available on-line: http://disc.ifas.ufl.edu/bloom. The on-line version is in black and white and does not list the hour or the predicted bloom date. 

Additional advisories will follow this preliminary one, roughly bi-weekly, and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

See last year's background introduction for previous responses: FLOWER BUD INDUCTION ADVISORY #1 for 2012-2013.
If you have any questions, please contact me (albrigo@ufl.edu)

FLOWER BUD INDUCTION ADVISORY #2 for 2013-2014-12/03/13

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom. This website was temporarily down but is running now.

Current Status - The projection is for a Neutral ENSO winter and moderate cool temperature accumulation. However, the accumulated hours below the threshold for induction, <68° F, through December 1 were <300 to 550 from southern to northern citrus areas. Another 30 to 50 hours are predicted for the next week. The minimum hours in southern areas will be about 400 hours less than the desired 850 after next week. Please note that the on-line Flowering Monitor System is not recording hours for the Indian River. The previous site at Ft. Pierce had its name changed and we did not catch that. Hopefully, we can get Indian River recognized by the program soon.

In order to improve the induction level beyond a minimum, trees should remain at rest at least through Christmas. Three more weeks of induction may add another 300 hours, which would bring the East Coast growing areas to near 700 hours, an acceptable level of flowering for an economic crop. A level of near 750-800 hours should be reached in most growing areas north of Sebring in three more weeks if cooler temperatures persist. Particularly in southern growing areas remember to watch the weather reports. If daytime high temperatures are projected to be in the mid-80 degree range in any of the next 3 weeks be sure that soil moisture is low to avoid initiation of bud growth. This can allow later cool weather to still influence bud induction, but if buds start to grow in a warm period their flowering potential is set at the level they had reached at the beginning of the warm weather. Induction levels are now high enough that a warm period will easily initiate bud growth in the 1st and 2nd terminal buds. I am concerned that induction levels are still low and need some cool weather help, particularly in the southern growing areas. An alternative to drought stress is to enhance flower bud induction with a stress inducing spray of urea or PO3 at the beginning of a winter warm period after more than 600 hours of cool temperatures accumulate.

If cool temperatures continue for 3 weeks, flower enhancing sprays may not be needed in southern areas. The exceptions could be trees with a heavy crop and/or weak root systems due to high water levels this past summer and fall. Weak root systems from HLB may also be a problem. If with additional cool temperatures 800 hours below <68 o F is not reached, a flower bud induction enhancement spray of urea or a phosphorous acid product sprayed during the early part of the warm period probably will be effective. Growers can consider applying either 53 to 60 lbs of foliar urea/acre or a PO3 product at 3 pints to 2 quarts per acre depending on which product is used (60 % P (3pts) or if 26 % P (2 qts)). The chosen material should be applied in 80 to 125 gal of water early in a warm period. These products apparently increase the stress level and enhance the amount of flowering induced by the cool temperatures. We have not tested these sprays on HLB affected trees, but these trees, if not severely declined, may also respond.

Don’t forget that winter freezes occur most often between Christmas and 15 January. Moderate drought stress increases cold hardiness on healthy trees, also increases flower bud induction and prevents bud growth in warm weather. However, drought stress is likely to increase preharvest fruit drop now, particularly in Hamlins and early mandarins with HLB. Again follow the weather for cold and warm periods. What a dilemma.

I will post an advisory before 20 December, earlier if a major change in weather is predicted. If you have any questions, please contact me (albrigo@ufl.edu).

FLOWER BUD INDUCTION ADVISORY #1 for 2012-2013-11/13/12

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom
If you are not familiar with the website and flower bud induction in citrus you should read the overview section below the current status paragraph.

Flowering related to the current 2012 -13 Fall-Winter –The previous medium crop and general tree recovery without a hurricane led to more typical flowering responses in Florida. The crop per tree is therefore above moderate in most groves and will make higher amounts of induction necessary for higher flowering levels next spring. This is supposed to be an ENSO-Neutral winter with average cool temperature accumulation and rainfall. October was warm until late, but November has been reasonably cool. Currently, citrus locations have accumulated low temperatures, < 68 degrees F, of 230 to 400 hours from southern to northern areas, respectively. The next 7 days will be intermediate for cool temperature accumulation with about 70 hours in the Indian River and more in other areas. Continued accumulation of cool temperatures and prevention of growth during a winter warm spell is more important for good 2012-13 citrus production. Trees will have enough cool temperature accumulation by next week to be stimulated to grow by a week to 10 days of warm weather (mid 80s). Therefore, start to monitor irrigation amounts so drought stress can quickly occur by stopping irrigation if a warm period is projected between now and Christmas or warm temperatures occur before reaching an acceptable level of over 750-800 hours of cool temperatures. Prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory after December 3rd. Remember drought stress adds to flower bud induction, just avoid excessive drought to maintain adequate condition of the current crop.

Overview of flower bud induction in Florida – Citrus flower bud induction starts in the fall and usually is completed by early January. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F, 19 0C). Periods of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be an ENSO-La Niña year, above average temperatures and lower than average rainfall. Under these conditions, enough hours of low temperatures below 68 degrees F. still usually accumulate to induce an economic level of flower buds. Conditions that can interfere with good flower bud induction include: 1) several warm periods interrupting the induction process or 2) the previous crop was exceptionally high or 3) leaf loss from hurricanes, freezes or other causes (canker) were excessive and tree recovery was not complete. Excessive leaf loss leads to low carbohydrate levels in developing buds which reduces their ability to become flower buds. None of these adverse conditions appear to be in play for the coming season’s flower bud induction. The biggest concern should be too many warm periods causing early initiation of bud growth before good flower induction.

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 800 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction may occur after 700-750 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures > 80 to 85 degrees F., can trigger growth (bud swelling) if a minimum total hours of low temperatures have accumulated (300-400 hours below 68 degrees F). Later in the winter when the accumulated cool temperature induction hours are high, fewer days and lower daytime highs (75 degrees F.) are required in a warm period to stimulate growth of buds. Weather information relative to Florida citrus flower bud development for the current and several previous years (back to 1998) can be obtained from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. An 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt for the next week. Find this information at: http://www.nws.noaa.gov/mdl/forecast/text/state/FL.MRF.htm. This is an easy way to see if a warm period, which could trigger flower bud growth, is predicted for your specific area in Florida.

Some flower buds will be induced in the range of 300 to 450 accumulated hrs < 68 degrees F. Warm events just after these levels of induction result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well watered. The first situation results in multiple cohorts of flower buds developing to different bloom dates. The second condition leads to low flowering-fruit set and excessive early spring vegetative growth. During the years from 1963 to 2003, multiple blooms occurred in over half of the years. Historically, the time period in which an early warm period (7-12 day) can lead to an initial low number of buds growing and flowering is roughly mid-November to mid-December. Then after more cool temperatures additional flower buds are induced and a later warm period starts their growth and repeats of this process result in multiple blooms. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is sufficient drought stress to stop growth. This water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts for cool periods. Sufficiently cool temperatures after a cold front rain will usually prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. In recent studies, Valencia trees in Central Florida have had good flowering and no apparent impact on current crop when irrigation was stopped in early December and resumed in the Spring. Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus’. Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering, respectively. If the current crop is very heavy, then more cool induction is needed to compensate for the crop load effect. If the current crop is lighter or tree condition better, then fewer total cool temperature hours are needed for an equal level of flowering. Recommendations (bottom text) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process. The system is available on-line: http://disc.ifas.ufl.edu/bloom

Additional advisories will follow this preliminary one, roughly bi-weekly) and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

Previous responses -- In the winter of 2001-2002 following a good crop, cool temperature accumulation was very slow and few hours accumulated (640 hours), warm temperatures persisted and most buds started to grow by 20 December, particularly in well irrigated blocks, leading to excessive vegetative buds. This resulted in few buds remaining for a second flowering wave and a relatively small crop occurred in the 2002-03 harvest season. By late December in the winter of 2002-2003, 850 hours of uninterrupted cool inductive temperatures had accumulated with a low current crop on the trees. The subsequent warm period initiated growth of almost all the buds on all of the spring and summer flush with bloom in early March. We had a fairly leafy bloom of very short duration (slightly more than 2 weeks). In spite of the high temperatures during and following bloom, an excellent fruit set occurred in all round oranges resulting in the highest Florida citrus crop forecast by the Florida Agric. Statistical Service (2003-04 crop). In the winter of 2003-2004, there was good flower bud induction and reasonably good fruit setting conditions, although the heavy previous crop probably reduced flowering levels and set. Even though fruit size was small, it looked like we were headed for a 220 million box orange yield before the 2004 hurricanes significantly reduced the 2004-05 yield. Since then, we have had Hurricane Wilma in 2005 and a long period of tree recovery from the 2004 and 2005 hurricanes. Since the hurricanes, flowering levels have been lower and appeared to require more hours to get adequate bloom. This has usually resulted in the main bloom occurring later (late March). There is some indication that tree recovery after the multiple hurricanes took several years. For the 2008-2009 crop season, accumulated hours below 68 degrees F were more than acceptable by the second warm period (over 1000 hours) but flowering and crop per tree was still low resulting in an estimate of only 134 million boxes of oranges. This low yield probably indicates that the trees still were not fully recovered from hurricane effects. Some details of the hurricane effects can be reviewed in the 11/01/2006 summary-introduction for the previous year’s flower induction cycle.

New insight- Recent studies from our lab have shown that cool temperatures and drought additively increase flower bud induction. They both up-regulate the flowering signal gene (CsFT) from the leaves. The signal protein produced by this gene travels to the bud to signal other genes to be up-regulated for flowering to commence as soon as warm temperatures and soil moisture are available. Continued drought inhibits these genes to be up-regulated until the drought stress is relieved by irrigation or rainfall.

If you have any questions, please contact me (albrigo@ufl.edu).

FLOWER BUD INDUCTION ADVISORY #2 for 2012-2013-12/3/12

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom. This website was temporarily down but is running now.

Current Status: The projection is for a Neutral ENSO winter and moderate cool temperature accumulation. The accumulated hours below the threshold for induction, <68° F, through December 1 were 500 to 750 from southern to northern citrus areas. Another 80 to 90 hours are predicted for the next week. The minimum hours in southern areas will be about 270 less than the desired 850 after next week.d.

In order to improve the induction level beyond a minimum, trees should remain at rest at least through Christmas. Three more weeks of induction may add another 300 hours, which would bring the East Coast growing areas to near 850 hours, a good level of flowering for an economic crop. A level of near 800 hours should be reached in most growing areas north of Palmdale in two more weeks if current temperatures persist. Particularly in southern growing areas remember to watch the weather reports. If daytime high temperatures are projected to be in the mid-80 degree range in the next 3 weeks, before Christmas, be sure that soil moisture is low to avoid initiation of bud growth. This can allow later cool weather to still influence bud induction, but if buds start to grow in a warm period their flowering potential is set at the level they had reached when the warm weather started. Induction levels are now high enough that a warm period will easily initiate bud growth in the 1st or 2nd terminal buds.

If cool temperatures continue for 3 weeks, flower enhancing sprays may not be needed in southern areas. The exceptions could be trees with a heavy crop and/or weak root systems due to high water levels this past summer and fall. If with additional cool temperatures 800 hours below <68 o F is not reached, a flower bud induction enhancement spray of urea or a phosphorous acid product sprayed during the early part of the warm period probably will be effective. Growers can consider applying either 53 to 60 lbs of foliar urea/acre or a PO3 product at 3 pints to 2 quarts per acre depending on which product is used (60 % P (3pts) or if 26 % P (2 qts)). The chosen material should be applied in 80 to 125 gal of water early in a warm period. These products apparently increase the stress level and enhance the amount of flowering induced by the cool temperatures. We have not tested these sprays on HLB affected trees, but these trees, if not severely declined, may also respond.

Don’t forget that winter freezes occur most often between Christmas and 15 January. Moderate drought stress increases cold hardiness on healthy trees, also increase flower bud induction and prevents bud growth in warm weather. Again follow the weather for cold and warm periods.

I will post an advisory before 14 December, earlier if a major change in weather is predicted. If you have any questions, please contact me (albrigo@ufl.edu).

FLOWER BUD INDUCTION ADVISORY #3 for 2012-2013-12/19/12

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

Current Status: The accumulated hours below the threshold for induction, <68° F, through December 18 were 650 to 1000 from southern to northern citrus areas. Another 100+ hours are predicted for the next week. The minimum hours in southern areas will be about 100 less than the desired 850 after next week. That is the good news. The not as good news is that bud growth, probably mostly first 2 or 3 buds at terminal shoot ends, have initiated growth and bloom dates for this cohort of growing buds is late January to early February. Since cooler weather is usual in January the actual bloom dates will probably be later, but potentially still earlier than normal. Now back to better news. Weather projections call for cool weather with good induction conditions until Christmas. There appears to be a warming trend coming the Sunday before Christmas. Sebring is expected to go from a daily high of 70 to 75 and then 80° F on Christmas day. If weather continues in the 80s for Christmas week, you can expect a second cohort of buds to start growing. That would be a good time to apply a stress enhancing spray, particularly in southern citrus growing areas.

If with additional cool temperatures 800 hours below <68° F are not reached, a flower bud induction enhancement spray of urea or a phosphorous acid product sprayed during the early part of the warm period probably will be effective. Growers can consider applying either 53 to 60 lbs of foliar urea/acre or a PO3 product at 3 pints to 2 quarts per acre depending on which product is used (60 % P (3pts) or if 26 % P (2 qts)). The chosen material should be applied in 80 to 125 gal of water early in a warm period. These products apparently increase the stress level and enhance the amount of flowering induced by the cool temperatures. We have not tested these sprays on HLB affected trees, but these trees, if not severely declined, may also respond.

Don’t forget that winter freezes occur most often between Christmas and 15 January. Freezes usually occur when a southern dip occurs in the Jetstream over the mid-West allowing cold arctic air to rapidly travel south before it can warm up. As of today, the Jetstream pattern is mostly laminar with a weak southern dip in the upper northwest, therefore so far so good. Moderate drought stress increases cold hardiness on healthy trees, also increases flower bud induction and prevents bud growth in warm weather. Remember that moderate drought stress can be a useful tool. Again follow the weather for cold and warm periods and act accordingly.

If you have any questions, please contact me (albrigo@ufl.edu).

FLOWER BUD INDUCTION ADVISORY #4 for 2012-2013-1/2/13

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

Current Status: The accumulated hours below the threshold for induction, <68 o F, through January 1st were 800 to 1400 from southern to northern citrus areas. Another 100+ hours are predicted for the next week. All citrus areas will have adequate induction levels after another 7 days. Except for the River District, all areas have one to 3 cohorts of flower buds developing at this time with bloom dates predicted from late January until March 1st. Since cooler weather is usual in January the actual bloom dates will probably be later, but potentially still earlier than normal. At this time, I don’t recommend any flowering enhancement sprays since induction levels are good.

Don’t forget that winter freezes often occur up to 15-20 January. Freezes usually occur when a southern dip occurs in the Jetstream over the mid-West allowing cold arctic air to rapidly travel south before it can warm up. There are no immediate freeze warnings, therefore so far so good.

FLOWER BUD INDUCTION ADVISORY #5 for 2012-2013-1/11/13

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

Current Status: With the warm weather this week, flower bud induction is most likely ended for this season. Except for the Indian River district with only one flower bud growth initiation event, all other citrus areas have 2 to 3 cohorts of flower buds in some stage of growth. The first cohort of flower buds was initiated with about 650 accumulated hours below the threshold for induction, <68 o F. Umatilla had another 100 hours while Ft. Pierce did not have initiation of growth in this period. Projected full bloom dates for this cohort of flower buds is the last week in January. It appears that this cohort is small and that the second will be a stronger bloom. This second cohort initiated growth after 800 to 900 hours of induction and the full bloom date is projected for mid-February, 15th to 21st. The third or last wave has 850 to 1100 hours of induction and the full bloom date is predicted for the first week in March. The least induction has occurred in the Indian River and south Florida areas with about 850 hours, which still should be adequate. Also this should be an early bloom year.

The early bloom makes the trees much more susceptible to a late freeze. Freezes usually occur when a southern dip occurs in the Jetstream over the mid-West allowing cold artic air to rapidly travel south before it can warm up. The only dip in the Jetstream is in the northwest so there are no immediate freeze warnings. Two more weeks should get us past the most likely freeze period, but even a light frost in mid to late February could be damaging to the flowers that should be developed by then.

FLOWER BUD INDUCTION ADVISORY #6 for 2012-2013-4/09/13

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

Current Status: At the last advisory in January, the issue was warm weather pushing the development of the flower buds to a very early bloom. That may have been the last consistent warm weather we have had until now. We did have a very light bloom in February followed by a moderate bloom in the first half of March. Everything was on track for flowering ending in early to mid-March, but the weather turned cool and flower development stopped. This occurred at a transition between early-mid oranges and Valencia bloom, which is usually a few days later due to the effect of the current crop delaying bloom. Instead of mid-March, we now have Valencia bloom just completing its flowering cycle on 9 April. The Valencia bloom dates are within the historical spring bloom period for Florida citrus. For some time it looked like Valencia bloom would be very sparse. Now it appears to be an average bloom.

The last stages of flower development are very sensitive to cooler temperatures and development just stops under these conditions, but it did not affect the level of flowering. For Central Florida, the three cohorts of flowers were still produced after about 650 accumulated hours below the threshold for induction, <68 o F; after 800 to 900 hours of induction, and the last wave had 850 to 1100 hours of induction. The least induction occurred in the Indian River and south Florida areas with about 850 hours, which still should be adequate.

Now instead of an overall early bloom year, we have early flowering cultivars early and later blooming Valencia and mandarins fairly late in the flowering season. This will probably result in early maturity for early-mid season oranges and a significant gap before the Valencia crop is ready for harvest for processing. Valencia fruit should have a much wider range of internal quality on each tree than normal since some much earlier bloom occurred on the same trees that are now in bloom to petal fall stages for their last flowering cohort.

Early-mid cultivars will probably start the May-June drop period no later than early May, but Valencia and mandarin cultivars may be as late as early June before they shed excess fruit. A final advisory will assess overall crop potential on healthy trees at the end of June.

FLOWER BUD INDUCTION ADVISORY #1 for 2011-2012-11/23/11

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom
If you are not familiar with the website and flower bud induction in citrus you should read the overview section below the current status paragraph.

Overview of flower bud induction in Florida – Citrus flower bud induction starts in the fall and usually is completed by early January. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F, 19 0C). Periods of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be an ENSO-La Niña year, above average temperatures and lower than average rainfall. Under these conditions, enough hours of low temperatures below 68 degrees F. still usually accumulate to induce an economic level of flower buds. Conditions that can interfere with good flower bud induction include: 1) several warm periods interrupting the induction process or 2) the previous crop was exceptionally high or 3) leaf loss from hurricanes, freezes or other causes (canker) were excessive and tree recovery was not complete. Excessive leaf loss leads to low carbohydrate levels in developing buds which reduces their ability to become flower buds. None of these adverse conditions appear to be in play for the coming season’s flower bud induction. The biggest concern should be too many warm periods causing early initiation of bud growth before good flower induction.

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 800 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction may occur after 700-750 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures > 80 to 85 degrees F., can trigger growth (bud swelling) if a minimum total hours of low temperatures have accumulated (300-400 hours below 68 degrees F). Later in the winter when the accumulated cool temperature induction hours are high, fewer days and lower daytime highs (75 degrees F.) are required in a warm period to stimulate growth of buds. Weather information relative to Florida citrus flower bud development for the current and several previous years (back to 1998) can be obtained from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. An 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt for the next week. Find this information at: http://www.nws.noaa.gov/mdl/forecast/text/state/FL.MRF.htm. This is an easy way to see if a warm period, which could trigger flower bud growth, is predicted for your specific area in Florida.

Some flower buds will be induced in the range of 300 to 450 accumulated hrs < 68 degrees F. Warm events just after these levels of induction result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well watered. The first situation results in multiple cohorts of flower buds developing to different bloom dates. The second condition leads to low flowering-fruit set and excessive early spring vegetative growth. During the years from 1963 to 2003, multiple blooms occurred in over half of the years. Historically, the time period in which an early warm period (7-12 day) can lead to an initial low number of buds growing and flowering is roughly mid-November to mid-December. Then after more cool temperatures additional flower buds are induced and a later warm period starts their growth and repeats of this process result in multiple blooms. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is sufficient drought stress to stop growth. This water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts for cool periods. Sufficiently cool temperatures after a cold front rain will usually prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress.

Presently, the only management tools available to eliminate or reduce the chance of multiple blooms are sufficient drought stress to stop growth or a timely gibberellin (GA) spray at the initiation of first wave bud growth. Water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality in healthy trees. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts for cool periods. Sufficiently cool temperatures (< 70 degrees F maximums) after a cold front rain will usually prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. In recent studies, Valencia trees in Central Florida have had good flowering and no apparent impact on current crop when irrigation was stopped in early December and resumed in the Spring. Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus’. Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering, respectively. If the current crop is very heavy, then more cool induction is needed to compensate for the crop load effect. If the current crop is lighter or tree condition better, then fewer total cool temperature hours are needed for an equal level of flowering. Recommendations (bottom text) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process. The system is available on-line: http://orb.at.ufl.edu/DISC/bloom.

Additional advisories will follow this preliminary one, roughly bi-weekly) and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

Previous responses -- In the winter of 2001-2002 following a good crop, cool temperature accumulation was very slow and few hours accumulated (640 hours), warm temperatures persisted and most buds started to grow by 20 December, particularly in well irrigated blocks, leading to excessive vegetative buds. This resulted in few buds remaining for a second flowering wave and a relatively small crop occurred in the 2002-03 harvest season. By late December in the winter of 2002-2003, 850 hours of uninterrupted cool inductive temperatures had accumulated with a low current crop on the trees. The subsequent warm period initiated growth of almost all the buds on all of the spring and summer flush with bloom in early March. We had a fairly leafy bloom of very short duration (slightly more than 2 weeks). In spite of the high temperatures during and following bloom, an excellent fruit set occurred in all round oranges resulting in the highest Florida citrus crop forecast by the Florida Agric. Statistical Service (2003-04 crop). In the winter of 2003-2004, there was good flower bud induction and reasonably good fruit setting conditions, although the heavy previous crop probably reduced flowering levels and set. Even though fruit size was small, it looked like we were headed for a 220 million box orange yield before the 2004 hurricanes significantly reduced the 2004-05 yield. Since then, we have had Hurricane Wilma in 2005 and a long period of tree recovery from the 2004 and 2005 hurricanes. Since the hurricanes, flowering levels have been lower and appeared to require more hours to get adequate bloom. This has usually resulted in the main bloom occurring later (late March). There is some indication that tree recovery after the multiple hurricanes took several years. For the 2008-2009 crop season, accumulated hours below 68 degrees F were more than acceptable by the second warm period (over 1000 hours) but flowering and crop per tree was still low resulting in an estimate of only 134 million boxes of oranges. This low yield probably indicates that the trees still were not fully recovered from hurricane effects. Some details of the hurricane effects can be reviewed in the 11/01/2006 summary-introduction for the previous year’s flower induction cycle.

Current status for 2011-12 Fall-Winter -- The medium crop and general tree recovery without a hurricane have finally led to more typical flowering responses in Florida. This is supposed to be an ENSO-La Niña winter with below average cool temperature accumulation and less rainfall. Warm periods can interrupt the accumulation process but lower than average rainfall could make it easier to impose drought stress to prevent an early flowering wave. Currently, citrus locations have accumulated low temperatures < 68 degrees F of 240 to 510 hours from southern to northern areas, respectively. The next 7 days will be moderate for cool temperature accumulation with another 100 hours. Continued accumulation of cool temperatures and prevention of growth during a winter warm spell are important for good 2010-11 citrus production. Therefore, start to monitor irrigation amounts so drought stress can occur if a warm period occurs between now and Christmas or occurs before reaching an acceptable level of over 750-800 hours of cool temperatures. Prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory after December 5th.

FLOWER BUD INDUCTION ADVISORY #2 for 2015-2016-12/09/11

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The internet Expert System on intensity and time of bloom can be accessed anytime: http://disc.ifas.ufl.edu/bloom.

Current Status:This is projected as a La Nina year, and that has been holding true with considerably less cool weather than last year.
The accumulated hours below the threshold for induction, <68 o F through 12/07/2011, were 345 to 750 from southern to northern citrus areas, respectively. Another 80 to 90 hours are predicted for the next week. The minimum hours in southern areas are therefore about 200 less than at this same time last year, and there are about 100 fewer cool hours in northern areas.

In order to improve the induction level beyond a minimum, trees should remain at rest at least through Christmas and preferably in to the New Year in the South. Three more weeks of induction may add another 300 hours, which would bring the East Coast growing areas to near 700 hours, a minimum level of flowering for an economic crop. Preferably, buds should have been exposed to at least 900 hours of inductive temperatures. This level should be reached in most growing areas north of Palmdale. In southern growing areas, particularly, remember to watch the weather prediction reports. If daily high temperatures are projected to go back up into the mid-80 degree range in the next 3 weeks, before January 1st, be sure that soil moisture is maintained at a low level during the warm periods to avoid initiation of bud growth. This will allow later cool weather to still influence bud induction, but if buds start to grow in a warm period their flowering potential is set at the level they had reached when the warm weather started.

If cool temperatures continue for 3 weeks, flower enhancing sprays should not be needed from Central Florida north, but may still be beneficial in southern areas. The exceptions could be trees with a heavy crop and/or weak root systems due to high water levels this past summer and fall. If additional cool temperatures do not reach 800 hours below <68 o F a flower bud induction enhancement spray of urea or a phosphorous acid product sprayed during a warm period probably will be effective (See advisory 3 last year for spray concentration details).

Don’t forget that winter freezes occur most often between Christmas and early January. Moderate drought stress before a freeze increases cold hardiness on healthy trees and also increases flower bud induction. Again it is very important to follow the weather predictions for cold and warm periods for the next 3 to 4 weeks.

FLOWER BUD INDUCTION ADVISORY #3 for 2011-2012-12/20/11

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

If you are not familiar with the website and flower bud induction in citrus you should read the overview section in the first advisory this year.

Current Status: Not good: the Flowering Monitor Systems indicates that trees in all areas except the southern-most growing region had their first wave of flower buds start growth after the first week of December with accumulated hours below 68 o F at low induction levels from 630 to 750 hours. I hope you had your blocks under moderate water stress to prevent this early start of growth. The continuous daily highs of about 80 o F were sufficient to start growth. There are another 5 days of these temperatures predicted and the flower buds on trees in southern areas probably will be growing also if not prevented by drought. If bud growth on trees has been prevented, accumulated hours of flower bud induction are now above 700 in all areas except the Indian River, which is below 500. From Polk County north, accumulated induction hours were above 700 for the first wave of flower bud growth, minimally acceptable for economic flowering levels.

Since warm temperatures will continue for five more days, flower enhancing sprays will probably be beneficial, particularly for southern areas and if drought stress was not established. Growers can consider applying either 53 to 60 lbs of foliar urea/acre or a PO3 product at 3 pints to 2 quarts per acre depending on which product is used (60 % P (3pts) or if 26 % P (2 qts)). The chosen material should be applied in 80 to 125 gal of water preferably before Christmas. These products apparently increase the stress level and enhance the amount of flowering induced by the cool temperatures.

If you have successfully established drought stress, trees should still be at rest and the weather until New Year’s Day should be followed closely. After another 4 or 5 days of 80 o F, the temperatures are predicted to drop to the low 70s. As long as daytime highs stay near 70, the chance of tree growth should be minimal. If you get to the New Year without growth, flower bud induction levels should be adequate and normal irrigation can be resumed.

Have a Merry Christmas and New Year. The next advisory will be the first week of January.

FLOWER BUD INDUCTION ADVISORY #4 for 2011-2012-1/11/12

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

Current Status: Mother Nature has not been friendly, but the weather has lived up to a La Niña year. The Flowering Monitor Model indicates that a first wave of flower buds was initiated to grow between December 3rd and 12th depending on the location, earliest initiation was in mid-Florida. The inductive cool hours had reached 620 to 640 in southern areas and 650 to 800 in central and northern areas of Florida’s citrus industry. The full bloom dates for this first wave of flower buds is about February 7 to 17. After another 200 to 250 cool hours accumulated a second wave of flower buds was initiated to grow with accumulated hours of 830 to 1000 from South to North in the citrus belt. The projected full bloom dates for these buds is February 25th to 31st. Finally, a third wave of flowering is projected for Immokalee and the Central Florida area with growth initiated after 1000 to 1150 hours of cool inductive temperatures. The bloom from this flower bud initiation should be weak and peak about March 10th to 14th..

A computer model anomaly in all of this year’s flowering projections is the lack of a prediction of flower bud growth initiation in response to weather conditions in Ft. Pierce, where 750 hours of temperatures of 68 degrees F or lower have accumulated and warm weather periods have presumably occurred. The Flowering Monitor System does not show the initiation of any flower bud growth for this Indian River area. Induction levels are now adequate for all citrus areas, but the flowering will be very spread out from two or more bloom peaks.

In southern and central locations where irrigation was continued into December, many trees reportedly are now flushing with light flowering. I don’t see any extensive flowering in any of our nearby trees, but the occasional bud with popcorn flowers can be seen. A few terminal buds are swelling.

Some growers may still want to apply urea or phosphorous acid to boost flowering, but most bud development has probably already started and the value of these sprays now is questionable.

Remember that freezing temperatures can still occur until late January and frost damage is a slight possibility at bloom time, particularly since the first and second bloom waves will be earlier than normal.

To summarize our current status, we have 2 or 3 waves of flower buds now differentiating with full bloom predictions from mid-February to mid-March. The combination should provide an economic level of flowering but bloom should be very spread out making ideal timing of production practices difficult. The best procedure is probably to schedule for the largest bloom.

Growers that kept trees under drought stress in early December will probably avoid the early February bloom and should have a good bloom about the end of February. Now we can wait and see what really happens.

FLOWER BUD INDUCTION ADVISORY #5 for 2011-2016-2/28/12

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

Current Status: The Flowering Monitor Model indicates that a first wave of flower buds was initiated to grow between December 3rd and 12th depending on the location, earliest initiation was in mid-Florida. The inductive cool hours had reached 620 to 640 in southern areas and 650 to 800 in central and northern areas of Florida’s citrus industry. The full bloom dates for this first wave of flower buds were between February 1 and 17. On trees observed in Central Florida very few flowers were produced from this wave and currently not more than a few fruit of about ½ inch diameter are on the trees from this wave of flowers.

Finally, a third wave of flowering was projected for Immokalee and the Central Florida area with growth initiated after 1000 to 1150 hours of cool inductive temperatures. The bloom from this flower bud initiation should peak about March 10th to 14th according to the original Flowering Monitor System prediction. The model has moved the full bloom date up, but I don’t see it on the trees. On some trees this third wave is nearly equal in intensity to the second.

Ft. Pierce and Umatilla have continued to behave differently than other citrus locations according to the model. Each location had only two waves of flower buds growing with Umatilla being earlier and Ft. Pierce later. The model now predicts a third cohort of flower buds growing in Ft. Pierce with a full bloom date later in April but I don’t think buds are still available for that wave.

What to do about Valencia trees this year is not an easy decision. Do you drought stress to get flowers for next year’s crop and sacrifice some of this crop? Hopefully cool temperatures will start in January and you can avoid having to make this decision.

In Central Florida, tree to tree bloom intensity is highly variable and stage of development is also, with stressed (declining) trees blooming earlier as usual. HLB and citrus blight appear to be the primary reasons for the declining trees.

Overall, my assessment is that we have a moderate bloom. It is divided between two cohorts of flower buds which are 2 to 3 weeks apart in stage of growth depending on the location. It remains to be seen what kind of fruit set we will get from these two sets of flowers. The second drop wave should be over with in all areas except the Indian River by the end of May, at which time set can be evaluated. I don’t plan to make another evaluation until early June.

FLOWER BUD INDUCTION ADVISORY #6 for 2011-2012-7/12/12

This is a service to our citrus growers posted on the CREC website. The internet Expert System on intensity and time of bloom was recently moved to a different server and can be accessed anytime: http://disc.ifas.ufl.edu/bloom

Current Status: Overall, we had a moderate bloom. It was divided between three cohorts of flower buds which were 2 to 3 weeks apart in stage of growth depending on the location, and for most locations the first wave was negligible regarding intensity and fruit set. Total inductive cool hours ran from about 820 to 1100 for the two later flowering cohorts.

The fruit set period was favorable regarding temperatures and rainfall distribution for the East Coast, but rains were sparse in South and Central Florida until mid-May. I was able to see many groves in the Central Florida area and despite a moderate bloom and dryer March and April, fruit set was fairly good. Rainfall was excellent for the last half of May and June. I was not able to visit South Florida groves to see what their set was like.

In recent years the expected crop statewide is always a hard to estimate because of the continued loss of trees and the inability to accurately monitor this rapid change in tree census. However, the groves that I have seen look to have a similar to slightly better crop load than last year. I would expect this year’s crop to be down only by the reduced number of productive trees in the state.

FLOWER BUD INDUCTION ADVISORY #1 for 2010-2011-11/18/10

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is a fortnightly service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed anytime at the designated Web Site.

Overview of flower bud induction in Florida – Citrus flower bud induction starts in the fall and usually is completed by early January. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F). A period of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be an ENSO-La Niña year, above average temperatures and lower than average rainfall. Under these conditions, enough hours of low temperatures below 68 degrees F. usually accumulate to induce an economic level of flower buds. Conditions that can interfere with good flower bud induction include: 1) several warm periods interrupting the induction process or 2) the previous crop was exceptionally high or 3) leaf loss from hurricanes, freezes or other causes (canker) were excessive and tree recovery was not complete. Excessive leaf loss leads to low carbohydrate levels in developing buds which reduces their ability to become flower buds. Except for a few trees with freeze damage, none of these adverse conditions appear to be in play for the coming season’s flower bud induction.

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 800 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction may occur after 700-750 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures > 80 to 85 degrees F., can trigger growth (bud swelling) if a minimum total hours of low temperatures have accumulated (300-400 hours below 68 degrees F). Later in the winter when the accumulated cool temperature induction hours are high, fewer days and lower daytime highs (75 degrees F.) are required in a warm period to stimulate growth of buds. Weather information relative to Florida citrus flower bud development for the current and several previous years (back to 1998) can be obtained from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. An 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt for the next week.

Some flower buds will be induced in the range of 300 to 450 accumulated hrs < 68 degrees F. Warm events just after these levels of induction result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well watered. The first situation results in multiple cohorts of flower buds developing to different bloom dates. The second condition leads to low flowering-fruit set and excessive early spring vegetative growth. During the years from 1963 to 2003, multiple blooms occurred in over half of the years. Historically, the time period in which an early warm period (7-12 day) can lead to an initial low number of buds growing and flowering is roughly mid-November to mid-December. Then after more cool temperatures additional flower buds are induced and a later warm period starts their growth and repeats of this process result in multiple blooms. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is sufficient drought stress to stop growth. This water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts for cool periods. Sufficiently cool temperatures after a cold front rain will usually prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. In recent studies, Valencia trees in Central Florida have had good flowering and no apparent impact on current crop when irrigation was stopped in early December and resumed in the Spring. Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus’. Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering, respectively. If the current crop is very heavy, then the greener shaded bands should be broader (require more hours for the same level of flowering). If the current crop is lighter or tree condition better, then the colored bands should be narrower as the level of flowering will be as large with fewer total cool temperature hours. Although this representation does not appear on the working screen, recommendations (bottom text box) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process.

Additional advisories will follow this preliminary one, roughly bi-weekly) and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

Previous responses – In the winter of 2001-2002 following a good crop, cool temperature accumulation was very slow and few hours accumulated (640 hours), warm temperatures persisted and most buds started to grow by 20 December, particularly in well irrigated blocks, leading to excessive vegetative buds. This resulted in few buds remaining for a second flowering wave and a relatively small crop occurred in the 2002-03 harvest season. By late December in the winter of 2002-2003, 850 hours of uninterrupted cool inductive temperatures had accumulated with a low current crop on the trees. The subsequent warm period initiated growth of almost all the buds on all of the spring and summer flush with bloom in early March. We had a fairly leafy bloom of very short duration (slightly more than 2 weeks). In spite of the high temperatures during and following bloom, an excellent fruit set occurred in all round oranges resulting in the highest Florida citrus crop forecast by the Florida Agric. Statistical Service (2003-04 crop). In the winter of 2003-2004, there was good flower bud induction and reasonably good fruit setting conditions, although the heavy previous crop probably reduced flowering levels and set. Even though fruit size was small, it looked like we were headed for a 220 million box orange yield before the 2004 hurricanes significantly reduced the 2004-05 crop. Since then, we have had Hurricane Wilma in 2005 and a long period of tree recovery from the 2004 and 2005 hurricanes. Since the hurricanes, flowering levels have been lower and appeared to require more hours to get adequate bloom. This has usually resulted in the main bloom occurring later (late March). There is some indication that tree recovery after the multiple hurricanes took several years. For the 2008-2009 crop season, accumulated hours below 68 degrees F were more than acceptable by the second warm period (over 1000 hours) but flowering and crop per tree was still low resulting in an estimate of only 134 million boxes of oranges. This low yield probably indicates that the trees still were not fully recovered from hurricane effects. Some details of the hurricane effects can be reviewed in the 11/01/2006 summary-introduction for the previous year’s flower induction cycle.

Current status for 2010-11 Fall-Winter - The light to medium crops and general tree recovery without a hurricane have finally led to more typical flowering responses in Florida. This is supposed to be an ENSO-La Niña winter with below average cool temperature accumulation and less rainfall. Warm periods can interrupt the accumulation process but lower than average rainfall could make it easier to impose drought stress to prevent an early flowering wave. Currently, citrus locations have accumulated low temperatures < 68 degrees F of 350 to 570 hours from southern to northern areas, respectively. The next 7 days will be moderate for cool temperature accumulation with another 70 to 90 hours. Continued accumulation of cool temperatures and prevention of growth during a winter warm spell are important for good 2010-11 citrus production. Therefore, start to monitor irrigation amounts so drought stress can occur if a warm period occurs between November 20 and Christmas or occurs before reaching an acceptable level of over 750-800 hours of cool temperatures. Prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory after December 3rd.

See a previous background introduction for previous important yield responses to cool temperatures: FLOWER BUD INDUCTION ADVISORY #1 for 2012-2013.

FLOWER BUD INDUCTION ADVISORY #2 for 2010-2011-12/07/10

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is a fortnightly service to our citrus growers posted on the CREC website. The internet Expert System on intensity and time of bloom can be accessed anytime: http://orb.at.ufl.edu/DISC/bloom.

Current Status: In spite of projections that this is a La Nina year, the weather has been very cool with projections for another week with highs below the threshold for induction, <68 o F. This means that another 168 hours will be added to the current 540 to 830 accumulated cool hours from southern to northern citrus areas. The minimum hours in southern areas will therefore be about 700 at the end of another week (December 13th), which is near the minimum required for an economic bloom if the current crop is low to moderate..

In order to improve the induction level beyond a minimum, trees should remain at rest for at least another two weeks after that. With any help from the weather, even trees in the south should have been exposed to at least 900 hours of inductive temperatures. Remember, watch the weather reports and if daytime high temperatures are projected to go back up into the 80 degree range after next week and before January 1st be sure that soil moisture is low to avoid initiation of bud growth.

If cool temperatures continue past this week, flower enhancing sprays may not be needed in most cases. The exceptions could be trees with a heavy crop and/or weak root systems due to high water levels this past summer and fall. More about this next report, but if you anticipate this need be sure you have the urea or phosphorous acid product on hand or readily available from your supplier.

FLOWER BUD INDUCTION ADVISORY #3 for 2010-2011-12/21/10

This is a fortnightly service to our citrus growers posted on the CREC website. The internet Expert System on intensity and time of bloom can be accessed anytime: http://orb.at.ufl.edu/DISC/bloom

Current Status: The weather has continued to be cool with projections for another week to 10 days with highs near the threshold for induction, <68 o F. This means that another 130 to 150 hours will be added to the current 835 to 1150 accumulated cool hours from southern to northern citrus areas. The minimum hours in southern areas will therefore be above 975 hours of cool temperature induction at the end of another week (December 28th ), which will be 100 hours above the minimum required for a good economic bloom if the current crop is low to moderate. Therefore, it appears that bloom should be more than adequate for next year’s crop on healthy trees. One negative aspect of the recent weather is that at least 50 hours were less than 41 degrees F. These hours were probably not effective because the induction process apparently doesn’t proceed at temperatures colder than 41o F.

Trees in low areas may have sustained some damage from the recent freezing temperatures. Remember, if damaged leaves persist after a freeze, it indicates that the green tissue of the shoot was also damaged. The associated buds will be lost. If damaged leaves quickly abscised, the buds should be ok and will grow normally and most of these buds will be flower buds this year.

Even though we should have good flowering with the cool temperature induction that will have occurred by New Years, it is still a good idea to delay the beginning of bud growth until after 10 January. This will delay flowering to a more normal bloom date and delay loss of cold hardiness. This can be accomplished by keeping soil moisture low and having the trees in a slightly droughty condition so that the buds will not grow if a warm period occurs. With the high induction levels that are now present, the buds will begin to grow if daytime high temperatures reach the high 70s to 80 o F for just a few days. Remember, watch the weather reports and if daytime high temperatures are projected to go back up into the 80 degree range after next week keep soil moisture low to avoid initiation of bud growth.

Since cool temperatures will continue past next week, flower enhancing sprays are probably not needed. The exceptions could be trees with a heavy crop and/or weak root systems due to high water levels this past summer and fall. If a warm period that is forecast to last 5 or more days with maximum temperatures above 75-80 degrees F does occur before January 10th then with adequate soil moisture for growth, growers can consider applying either 53 to 60 lbs of foliar urea/acre or a PO3 product at 3 pints to 2 quarts per acre depending on which product is used (60 % P (3pts) or if 26 % P (2 qts)). The chosen material should be applied in 80 to 125 gal of water in the first 3 to 4 days at the beginning of the warm period. These products apparently increase the stress level and enhance the amount of flowering induced by the cool temperatures.

Have a Merry Christmas and New Year. The next advisory will be the first week of January.

FLOWER BUD INDUCTION ADVISORY #4 for 2010-2011-1/5/11

This is a fortnightly service to our citrus growers posted on the CREC website. The internet Expert System on intensity and time of bloom can be accessed anytime: http://orb.at.ufl.edu/DISC/bloom

Current Status: Happy New Year and Surprise-Surprise. While we celebrated the holidays, apparently Mother Nature was busy. The Flowering Monitor Model indicates that a first wave of flower buds was initiated to grow between December 17th and 28th depending on the location. The inductive cool hours had reached 800 to 940 in southern areas and 1000 to 1250 in central and northern areas of Florida’s citrus industry. The full bloom dates for this first wave of flower buds is about February 24 to 25 in southern, flatwoods areas and March 2 to 7 for central and northern areas. Since that time another 300 hours have accumulated so that hours of inductive temperatures have now reached 1100 to 1500 hours from South to North in the citrus belt. Induction levels are now good to excellent for all citrus areas

The initiation of bud growth has occurred with temperatures in the 70 to 80 o F range lasting 6 to 7 days, often with a couple of days in the 60s. This doesn’t seem to be a strong initiating warm period for bud growth, and therefore I expect another wave of flower buds to initiate growth when the next warm period occurs. The one exception may be the south western citrus area around Immokalee. This area had 10 days from 68 to 79 o F and will have warmer weather this week. All other citrus areas will probably respond to the next warm period, which isn’t predicted for the next 8 to 10 days.

Some growers still want to apply urea or phosphorous acid to boost flowering. Trees most likely to respond are on shallow soils where root systems are usually compromised. To obtain enhanced flowering from one of these sprays in the south western areas requires immediate application. All other areas should wait until several days in the 70 o F range are predicted by the weather service and the spray should be applied at the beginning of the warmer period. With the high levels of cool temperature induction, I question whether any benefit will occur. For more details regarding these sprays, see the last advisory (#3).

As a reminder about damage from the recent freezing temperatures, remember if damaged leaves persist after a freeze, it indicates that the green tissue of the shoot was also damaged. The associated buds will likely be lost. If damaged leaves quickly abscised, the buds should be ok and will grow normally and most of these buds will be flower buds this year. An assessment of how much reduction in crop may occur next year may be gained by evaluating how much of last year’s spring and summer shoots appear to be damaged based on non-abscising dead leaves. Actual damage is usually not clear until the spring growth starts and is or is not sustained by the supporting wood below the buds.

FLOWER BUD INDUCTION ADVISORY #5 for 2010-2011-1/18/11

This is a fortnightly service to our citrus growers posted on the CREC website. The internet Expert System on intensity and time of bloom can be accessed anytime: http://orb.at.ufl.edu/DISC/bloom

Current Status: The Flowering Monitor Model indicated that a first wave of flower buds was initiated to grow between December 17th and 28th depending on the location. The inductive cool hours had reached 800 to 940 in southern areas and 1000 to 1250 in central and northern areas of Florida’s citrus industry. The model now indicates that a second wave of flower buds has been initiated to grow in all areas from Sebring and to the south with 1030 to 1220 hours below 68 o F. The full bloom dates for the first wave of flower buds are about February 22 to 25 in southern, flatwoods areas and March 1 to 8 for central and northern areas. The second wave will bloom about March 4th to 11th.

Induction levels are now excellent for all citrus areas and raise the possibility of too many flowers on mandarin and seedless cultivars such as navel and Ambersweet, particularly if the current crop was low. For areas south of Sebring it may be too late to reduce flowering levels with a GA3 (gibberellin) spray, but for areas north of Sebring this week may be an excellent time to prevent more flowering. Temperatures are projected to be in the mid-70s for 3 to 4 days. This will likely cause initiation of more flower bud growth where only one wave has started so far. A single spray of 20 ppm in 80 to 125 gal of water per acre is the recommended rate. Pro-Gibb will have an active ingredient (ai) rate/acre on the label.

Some growers may still want to apply urea or phosphorous acid to boost flowering. Only trees north of Sebring may show enhanced flowering from one of these sprays but application would be required this week while temperatures are in the mid-70s, however a response is less likely since induction levels are fairly high. For more details regarding these sprays, see advisory #3.

FLOWER BUD INDUCTION ADVISORY #6 for 2010-2011-2/03/11

This is a fortnightly service to our citrus growers posted on the CREC website. The internet Expert System on intensity and time of bloom can be accessed anytime: http://orb.at.ufl.edu/DISC/bloom

Current Status: The Flowering Monitor Model indicates that in addition to a first wave of flower buds with growth initiated between December 17th and 28th a second wave of flower bud initiation occurred for locations south of Lake Alfred, both Ridge and Flatwood Districts, but no second wave of flower bud development is indicated by the model for Lake Alfred or northern locations. The inductive cool hours were 800 to 940 in southern areas and 1000 to 1250 in central and northern areas of Florida’s citrus industry for the first wave of growth. The second wave of flower buds had growth initiated after 1030 to 1220 hours below 68 o F. The full bloom dates are about February 19 to 27 in locations from Sebring south including the flatwoods. Central and northern areas should have full bloom March 3 to 7. The second wave will bloom about March 1st to 9th, 2 or 3 days earlier than the model projected in January.

Induction levels are now excellent to excessive for all citrus areas. The buds are breaking at Lake Alfred. Pinhead flowers could be seen this week on navel and Hamlin trees. Buds are pushing on some shoots in Valencia and grapefruit. No bud push was observed yet on mandarin trees, which usually bloom 10 to 14 days after oranges.

The projected bloom dates would be delayed if cooler than normal weather occurs the rest of February. In another two weeks we should be able to tell if a second wave of flower buds was induced, but the model has been fairly accurate in projecting number of flower bud waves that will grow in a spring season

FLOWER BUD INDUCTION ADVISORY #6 for 2010-2011-2/15/11

This is a fortnightly service to our citrus growers posted on the CREC website. The internet Expert System on intensity and time of bloom is not functioning due to loss of the server on which it was housed. If it becomes accessible it should be available at: http://orb.at.ufl.edu/DISC/bloom
Current Status: According to the Flowering Monitor Model there has been no change in the predicted bloom dates. An earlier warm period was off-set by a cooler than normal period according to the model. The inductive cool hours were 800 to 940 in southern areas and 1000 to 1250 in central and northern areas of Florida’s citrus industry for the first wave of growth. The second wave of flower buds had growth initiated after 1030 to 1220 hours below 68 o F. The full bloom dates projected were about February 18 to 27 in locations from Sebring south including the flatwoods. Central and northern areas had full bloom projected for March 3 to 7. The second wave was projected to bloom about March 1st to 9th, 2 or 3 days earlier than the model projected in January.
Observations in the field indicate that the projected bloom dates are too early as the most advanced buds still have a few tight white flowers, but most are still pin-head or smaller. The Ft. Pierce and Immokalee projections were for full bloom in 2 to 3 days, which can’t happen at the present stage of bloom. The weather service is projecting a warmer 7 days, which should accelerate flower development. Full bloom in some areas could be late February or early March, but not this week.
Flower buds are now inflorescences with many new stems of 2 to 3 cm length. In trees observed locally, pin-head flowers, usually with leaves, were observed at 4 to 6 nodes. Some of the inflorescences had as many as 5 flowers and leaves. Developing leaves associated with the flowers indicates a better chance for set. In judging how good a bloom will occur on your trees, remember that in most years at least 80 % of the flowers occur in the first 4 buds of Hamlin or Valencia orange trees. If you find on average that 6 or more leaf axial buds are flowering, then you can expect a better than average flowering intensity.

FLOWER BUD INDUCTION ADVISORY #1 for 2009-2010-11/12/09

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

This is a weekly or biweekly service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site.

Overview of flower bud induction in Florida – Citrus flower bud induction starts in the fall and usually is completed by early January. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F). A period of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be an ENSO-El Niño year, below average temperatures and higher than average rainfall. Under these conditions, more than enough hours of low temperatures below 68 degrees F. usually accumulate to induce a high level of flower buds. Conditions that can interfere with good flower bud induction include: 1) several warm periods interrupting the induction process or 2) the previous crop was exceptionally high or 3) leaf loss from hurricanes, freezes or other causes (canker) were excessive and tree recovery was not complete. Excessive leaf loss leads to low carbohydrate levels in developing buds which reduces their ability to become flower buds. Except for a few trees with freeze damage, none of these adverse conditions appear to be in play for the coming season’s flower bud induction.

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 800 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction may occur after 700-750 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures > 80 to 85 degrees F., can trigger growth (bud swelling) if a minimum total hours of low temperatures have accumulated (300-400 hours below 68 degrees F). Later in the winter when the accumulated cool temperature induction hours are high, fewer days and lower daytime highs (75 degrees F.) are required in a warm period to stimulate growth of buds. Weather information relative to Florida citrus flower bud development for the current and several previous years (back to 1998) can be obtained from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. An 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt for the next week. Find this information at: http://www.nws.noaa.gov/mdl/forecast/text/state/FL.MRF.shtml. This is an easy way to see if a warm period, which could trigger flower bud growth, is predicted for your specific area in Florida.

Some flower buds will be induced in the range of 300 to 450 accumulated hrs < 68 degrees F. Warm events just after these levels of induction result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well watered. The first situation results in multiple cohorts of flower buds developing to different bloom dates. The second condition leads to low flowering-fruit set and excessive spring vegetative growth. During the years from 1963 to 2003, multiple blooms occurred in over half of the years. Historically, the time period in which an early warm period (7-12 day) can lead to an initial low number of buds growing and flowering is roughly mid-November to mid-December. Then additional flower buds developing later results in multiple blooms. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is sufficient drought stress to stop growth. This water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts for cool periods. Sufficiently cool temperatures after a cold front rain will usually prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. In recent studies, Valencia trees in Central Florida have had good flowering and no apparent impact on current crop when irrigation was stopped in early December and resumed in the Spring. Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus’. Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering, respectively. If the current crop is very heavy, then the greener shaded bands should be broader (require more hours for the same level of flowering). If the current crop is lighter or tree condition better, then the colored bands should be narrower as the level of flowering will be as large with fewer total cool temperature hours. Although this representation does not appear on the working screen, recommendations (bottom text box) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process. The system will be available on-line again this year, but a new server location is being set-up. I will announce its location on our Website when it is available:

Bi-weekly advisories will follow this preliminary one and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

Previous responses -- In the winter of 2001-2002 following a good crop, cool temperature accumulation was very slow and few hours accumulated (640 hours), warm temperatures persisted and most buds started to grow by 20 December, particularly in well irrigated blocks, leading to excessive vegetative buds. This resulted in few buds remaining for a second flowering wave and a small crop occurred in the 2002-03 season. By late December in the winter of 2002-2003, we had 850 hours of uninterrupted cool inductive temperatures with a low current crop on the trees. The subsequent warm period initiated almost all the buds on all of the spring and summer flush to differentiate and bloom in early March. We had a fairly leafy bloom of very short duration (slightly more than 2 weeks). In spite of the high temperatures during and following bloom, an excellent fruit set occurred in all round oranges resulting in the highest Florida citrus crop forecast by the Florida Agric. Statistical Service (2003-04 crop). In the winter of 2003-2004, there was good flower bud induction and reasonably good fruit setting conditions, although the heavy previous crop probably reduced flowering levels and set. Even though fruit size was small, it looked like we were headed for a 220 million box orange yield before the 2004 hurricanes significantly reduced the 2004-05 crop. Since then, we have had Hurricane Wilma in 2005 and a long period of tree recovery from the 2004 and 2005 hurricanes. Since the hurricanes, flowering levels have been lower and even this past spring peak bloom required more hours and the main bloom occurred later (late March), probably because of continued tree recovery after the multiple hurricanes. For the 2008-2009 crop season, accumulated hours below 68 degrees F were more than acceptable by the second warm period (over 1000 hours) but flowering and crop per tree was still low resulting in an estimate of only 134 million boxes of oranges. This low yield probably indicates that the trees still were not fully recovered from hurricane effects. Some details of the hurricane effects can be reviewed in the 11/01/2006 summary-introduction for the previous year’s flower induction cycle.

Current status for 2009-10 Fall-Winter -- The light to medium crops and general tree recovery without a hurricane should lead to a more typical flowering response next spring in Florida. This is supposed to be an ENSO-El Niño winter with above average cool temperature accumulation. Warm periods can interrupt the accumulation process and higher than average rainfall could make it more difficult to impose drought stress to prevent an early flowering wave. Currently, citrus locations have accumulated low temperatures < 68 degrees F of 75 to 300 hours from southern to northern areas, respectively. The next 8 days will be good for cool temperature accumulation with another 70 to 90 hours. Continued accumulation of cool temperatures and prevention of growth during a winter warm spell are important for good 2009-10 citrus production. Therefore, start to monitor irrigation amounts so drought stress can occur if a warm period occurs between November 20 and Christmas or occurs before reaching an acceptable level of over 750-800 hours. Prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory.

 

FLOWER BUD INDUCTION ADVISORY #2 for 2009-2010-11/24/09

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data

Current Status for 2009-10 fall-winter -- Improved tree condition of non-HLB affected trees since the 2004-05 hurricanes should be promising for good flowering next spring if sufficient cool weather accumulation occurs. Through November 22nd, citrus locations had accumulated low temperatures (< 68 degrees F) of 180 to 440 hours from southern to most northern areas, respectively. The next 8 day forecast from NOAA calls for moderately cool temperatures, particularly Friday and Saturday with another 85 to 120 hours below 68 degrees F accumulating. By next week, the most northern FAWN site for citrus should have about 560 hours. The warmer southern areas will have about 300 hours. These values are 160 to 200 hours below last year, but similar to the previous year.

After the two cooler days at the end of the week, the trees will be fairly susceptible to growth stimulation during a warm period if soil moisture is adequate. The southern, central and northern citrus areas will take another 5, 4 and 3 weeks of moderately cool weather, respectively, to reach a minimum adequate flower bud induction level. Until that time, prevention of growth during a winter warm spell is very important to prevent initiation of early bud growth. Therefore, continue to monitor and reduce irrigation amounts so drought stress can easily and rapidly occur if a warm period occurs between now and Christmas. Maintenance of water stress during this period also is an alternative to having sufficient cool temperatures for flower bud induction. In recent studies, field trees held under some water stress had more flowers than trees irrigated during the winter.

At the very least, prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory. See last week’s background advisory for additional irrigation details.

The other side of winter conditions is concern for a freeze. In this El Niño ENSO winter, freezes are less likely. As long as the Jet Stream flow is mostly from West to East across the southern half of the US, no rapid Arctic Express cold air movement into Florida is likely. Check the Weather Underground on the CREC Weather links for easy access to Jet Stream patterns.

There are several useful Websites to follow weather forecasts. The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click. Alternative, an 8 day forecast can be viewed by going to www.crec.ifas.ufl.edu and click on resources> weather> 8-day forecast. Additionally, 10 day forecasts by city or zip code can be obtained from the Weather Channel, also in the CREC weather links. Remember during this critical period to view FAWN, use the on-line monitor site, when available, and the NOAA 8 day forecast. In the meantime, I will post weekly advisories. In order to prevent bud growth, trees should be slightly stressed if a warm period (7-10 days with maximum temperatures above 85 degrees F.) is predicted.

FLOWER BUD INDUCTION ADVISORY #3 for 2009-2010-12/03/09

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web site links for weather data. See below for website for the Flower Monitoring Program (FMP)

Current Status: Cool weather accumulation has continued and now it would be easy to stimulate flower bud growth and differentiation if a warm period were to occur. Fortunately, warm weather is not predicted for the next 7 to 10 days. The (FMP) indicates that 300 to 370 hours of cool temperatures have accumulated in southern citrus areas, 400 to 460 hours in central areas and 500 to 600 hours have accumulated in low, colder western areas (ONA) to the more northern locations. The next 8 day forecast from NOAA calls for moderately cool temperatures and another 70 to 140 hours below 68 degrees F should accumulate from south to north. This will leave the East Coast and Immokalee locations with a little less than have the minimum requirement or at about 350hours. The Central areas will have about 60 % of a good induction level (good equals 800 hours), while in another 7 days, the northern areas should have a minimal acceptable level of cool temperature accumulation or 700 hours. The cool fronts Thursday and this weekend will keep soil moisture high, but the cool weather will prevent any likelihood of a warm period for the next 10 days.

The Flowering Monitor Program is now on-line for those who wish to use it. Go to: http://orb.at.ufl.edu/DISC/bloom. The number of current hours below 68 degree F is correct, but it is not translating the NOAA 8 day forecast correctly and is estimating too many cool hours over the next week

I will continue to provide advisories weekly until this critical period until Christmas ends and we have sufficient flower bud induction or are faced with an early warm period that will initiate early flower bud development. If you have been spraying urea or PO3 at the beginning of the first warm period, particularly when total hours are marginally low, you should have product on hand.

In this El Nino ENSO winter, freezes are less likely. The Jet Stream flow should remain mostly horizontal from West to East across the southern two-thirds of the US so that rapid Arctic Express cold air movement into Florida is not likely. Check the Weather Underground on the CREC Weather links for easy access to Jet Stream patterns and watch it carefully over the next month for any significant change to a southern dip that can easily lead to freezing temperatures in Florida. I will report my assessment of this as we approach Christmas and the most likely freeze-hazard period.

There are two useful Websites to follow weather forecasts. The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click. Alternative, an 8 day forecast can be viewed by going to www.crec.ifas.ufl.edu and click on resources> weather> 8-day forecast.

FLOWER BUD INDUCTION ADVISORY #4 for 2009-2010-12/14/09

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data

Current status for 2008-09 fall-winter – Cool weather accumulation continued at a slow pace this pass week with the more northern locations now at 721 hours (Avalon) and 760 hours (Umatilla), with 600 hours in Central Florida and 475 and 340 hours in Immokalee and Ft. Pierce, respectively. The southern areas are still at half or less of the desired hours for induction of flower buds. An additional 60 to 100 hours will be accumulated in the next 7 days. This will bring the northern areas into the acceptable level induction, but the Central areas will need another two weeks of suitable temperatures and the Southern areas will need longer than that to reach suitable levels. At least the next 10 days appear to be ok with a cool front coming to lower temperatures into next week.

Regarding freeze risk, the Jet Stream pattern is favorable for minimal risk. All air flow is west to east with a slight upward movement in the southern area so that the Jet Stream is pulling moist air out of the Gulf into Florida. This may account for the extended period of humid, wet conditions (http://www.wunderground.com/US/Region/US/JetStream.shtml). It has been impossible to dry out the soil so we need to hope for continued moderate temperatures until we can accumulate enough cool weather for good flower bud induction.

There are two useful Websites to follow weather forecasts. The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click. Alternative, an 8 day forecast can be viewed by going to https://crec.ifas.ufl.edu/ and click on resources> weather> 8-day forecast. Remember during the critical freeze period to view FAWN, use the on-line monitor site provided in the first advisory and the NOAA 8 day forecast and watch the Jet Stream pattern.

In order to prevent or delay bud growth now that trees are at a moderate level of induction, trees should be slightly stressed if a warm period (5-7 days with maximum temperatures above 80 degrees F.) is predicted. Hopefully, we will dry out after the next front so that soil moisture can be controlled through the Christmas-New Year’s Holiday period.

FLOWER BUD INDUCTION ADVISORY #5 for 2009-2010-12/24/09

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data. This advisory will be the last until after New Year’s weekend as our Center will be closed over the holidays. I can be reached by email (see below) if you have an important question.

Current status for 2008-09 Fall-Winter – Finally air temperatures expected in an El Niño year have arrived. It appears that the next 9 days will also be favorable. Currently, citrus areas have from 460 to 950 hours of cool temperatures (below 68 degrees F). Through New Year’s Day these numbers should increase to 600 to 1130 from southern to northern citrus areas. Only the Indian River District will be short of a minimum acceptable number of cool hours after next week. This year the east coast district has had many fewer hours than Immokalee. In previous years these two areas have behaved similarly regarding cool hours for flower bud induction. The southern areas would be better off if they received another 200 hours after New Year’s Day.

Finally, a third wave of flowering was projected for Immokalee and the Central Florida area with growth initiated after 1000 to 1150 hours of cool inductive temperatures. The bloom from this flower bud initiation should peak about March 10th to 14th according to the original Flowering Monitor System prediction. The model has moved the full bloom date up, but I don’t see it on the trees. On some trees this third wave is nearly equal in intensity to the second.

Since there will be no update of this advisory until the week of January 4th, you should monitor the temperature forecast next week to be sure that cool temperatures will continue the first week of January. If warm temperatures are predicted (mid-80s or higher) for the southern areas (Sebring south), you should consider applying urea or PO3 within the first 3 to 4 days of the warm weather to groves in this area. These products are recommended at 25-28 lbs N as urea or 1½ -2½ quarts (high to low % product) of a phosphite salt per acre. Other citrus areas appear to be on their way to having adequate cool temperature induction.

Freeze potential– Although El Niño years generally do not produce freezes in Florida there is a deep North to South jet stream trough over the western US. Currently, the trough reaches Mexico before turning East so that southern air movement is coming across the Gulf of Mexico bring us moderated temperatures. If that trough moves eastward to the mid-west, we could get freezing temperatures. You should keep an eye on this development until after mid-January, when freeze probability diminishes.

Have a Merry Christmas and a Happy New Year.

FLOWER BUD INDUCTION ADVISORY #6 for 2009-2010-1/6/10

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data. This advisory will be the last until after New Year’s weekend as our Center will be closed over the holidays. I can be reached by email (see below) if you have an important question.

Freeze potential– Although freezes have not occurred in Florida’s citrus areas during El Niño years, it appears that string of good luck is broken. However, the deep North to South jet stream trough over the western US is still turning East over the Midwest or our temperatures would be much lower. The Jet Stream upper air movement is still coming across the Gulf of Mexico and moderating temperatures. The trough has moved eastward and the moderation is fairly weak. You should watch this development very closely over the weekend as it will influence how cold it gets with the next front. You can easily follow the Jet Stream pattern at http://www.wunderground.com/

Current status for 2009-10 Fall-Winter – Cool weather has been continuous for an unprecedented period of time. Currently, citrus areas have from 691 to 1200 hours of cool temperatures (below 68 degrees F). The next 7 to 10 days are forecast to stay cold and one week from now even the southern areas will be above 850 hours of cool temperature induction. This should be very satisfactory for good commercial flowering levels. As of now it appears that we should have one major bloom, but its predicted date is not yet determined.

As soon as warm weather returns the buds will initiate growth very easily. We have detected a few buds on some trees with bud swell, but the flower monitoring model does not indicate that a significant flowering flush has started to develop.

By the time temperatures get warm enough to push bud growth there probably will be no need to apply flowering enhancement sprays of urea or phosphite salts.

FLOWER BUD INDUCTION ADVISORY #7 for 2009-2010-1/13/10

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data. I can be reached by email (see below) if you have an important question.

Freeze damage and flowering– Ok, El Niños have lost their grip on holding off winter freezes in Florida citrus. However, considerable cold weather occurred the two weeks before the freezes, thus increasing tree cold hardiness. In Lake Alfred, there does not appear to be too much immediate leaf injury. Remember as a general rule, if leaves are injured and stick on the tree, there is usually twig damage behind those leaves. If damaged leaves easily abscise from the shoot, there is a minimum of wood damage. You can evaluate this within 7 to 10 days. If damaged leaves stick or abscise at the blade, it takes weeks to determine wood-cambial damage. The trees should have withstood the temperatures and durations reported (see FAWN station reports). Flowering will not be altered, even if many leaves fall off, unless there was twig and bud damage.

Freezing temperatures could have been more severe, but the Jet Stream upper air movement is still coming across the Gulf of Mexico and most likely moderated temperatures. The troughs are now over California and the East Coast with very weak upper air movement over the Midwest. This may allow for some rapid changes, so continue monitoring upper air movement. You can easily follow the Jet Stream pattern at http://www.wunderground.com/. Usually, the freeze hazard is past by January 25th , another 2 weeks.

Current status for 2009-10 Fall-Winter – Cool weather has been continuous for an unprecedented period of time. Currently, citrus areas have from 850 to 1400 hours of cool temperatures (below 68 degrees F) from southern to northern citrus growing areas. The next 7 days are forecast to stay cool and one week from now even the southern areas will be above 975 hours of cool temperature induction. This should be very satisfactory for good commercial flowering levels. The flowering monitor system has not indicated that flower buds have initiated growth, but it is likely they will start differentiation during the next 7 to 10 days of warmer weather from Sebring south. Temperature may remain too cool this coming week to initiate bud growth from Lake Alfred north. As of now it appears that we should have one major bloom. If bud growth does start in the next week, the earliest bloom date is probably March 10th. If temperatures are cooler than normal during the next 60 days, the bloom date should be later than mid-March.

Since 2004, citrus trees in Florida have not been responding well to cool temperature accumulations that were adequate in the past. After a slow start this year, flower bud induction temperature accumulation has been very good and normally flower enhancement sprays would not be called for, as I advised last week. But if you have experienced weak flowering the past two or three years and were planning on using a flowering enhancement spray of urea or phosphite salts, this next 7 days will be the time to apply it if you have citrus from Sebring south. Citrus trees in more northern areas are going to have exceptionally high flower bud induction levels, will not initiate bud growth until more than a week goes by and should not need a flowering enhancement spray.

FLOWER BUD INDUCTION ADVISORY #8 for 2009-2010-1/21/10

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data. I can be reached by email (see below) if you have an important question.

Freeze damage and flowering - In Lake Alfred, there still does not appear to be very much immediate leaf injury. Remember as a general rule, if leaves are injured and stick on the tree, there is usually twig damage behind those leaves. If damaged leaves easily abscise from the shoot, there is a minimum of wood damage. You can evaluate this within 7 to 10 days. If damaged leaves stick or abscise at the blade, it takes weeks to determine the extent of cambial damage. The trees should have withstood the temperatures and durations reported (see FAWN station reports). Flowering will not be altered, even if many leaves fall off, unless there was twig and bud damage.

Current status for 2009-10 Fall-Winter – Yes, according to the ‘flower monitoring system’ we have initiation of differentiation, but the model reports this event from Sebring north, not in the Immokalee or Ft. Pierce areas. Last we I guessed that ‘temperature may remain too cool this coming week to initiate bud growth from Lake Alfred north’, so what do I know. I still believe ‘we should have one major bloom’ and the model predicts the full bloom date will be March 20 to 22, depending on the location. Again, I think that in 1 to 3 days, the model will say that bud growth has started in the southern areas. Initiation of differentiation started with 1150 (Sebring) to 1450 (Umatilla) hours of inductive temperatures, very good levels of flower induction. Ft. Pierce and Immokalee are now at 964 and 1136 hours, which are also good.

Next week, we should see that flower bud growth has started in all areas and have predicted bloom dates for the southern areas.

FLOWER BUD INDUCTION ADVISORY #8 for 2009-2010-1/28/10

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data. I can be reached by email (see below) if you have an important question.

Current status for 2009-10 Fall-Winter –According to the ‘flower monitoring system’ citrus trees in all growing areas in Florida have initiated differentiation of flower buds. This initiation occurred after 890 (Ft. Pierce) to 1450 (Umatilla) hours of cool induction. The predicted full bloom dates are March 18 to 20, a 2 day advancement from last week.

About 150 to 200 additional cool hours have accumulated since the initiation of this first flowering wave. With another 100 hours and then a warm period, the model will predict a second wave. I don’t believe a second wave will happen because the first wave should account for most of the available buds. This first wave could be as strong as the 2003 bloom if the trees have fully recovered from their poor flowering responses since the 2004-05 hurricanes. The buds should be advanced enough to see how the bloom is developing by early March. As mentioned a couple of weeks ago, at least a few buds should develop earlier than the main wave, but how many is only a guess based on observations that some trees had a few shoots with bud swell.

FLOWER BUD INDUCTION ADVISORY #10 for 2009-2010-2/16/10

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data. I can be reached by email (see below) if you have an important question.

Current status for 2009-10 Fall-Winter –Due to the cool weather, full bloom dates have been pushed back a little. The predicted full bloom dates are 16-18 March in southern areas, 20 to 22 March in central areas and 23 to 24 March in northern areas. These dates may be pushed back a little more if cool weather continues. If however, the weather finally turned warm, the bud growth is advanced enough that full bloom could come very quickly.

In Central Florida, pinhead flowers can be seen with several leaves in most inflorescences. Only a few flower-only buds were observed. Weak trees may be at the popcorn stage. A scattering of inflorescences were observed that were near full bloom. These probably relate to the early bud swelling observed and reported on January 6th, report 6. Although most new growth appears to have a single flower surrounded by leaves, it is too early to tell whether additional flowers are present or not without dissecting the inflorescences. With the induction levels experienced this year, I would expect the most buds would produce more than one flower.

Unless unusual weather occurs, I will update these reports in two weeks, about March 2.

FLOWER BUD INDUCTION ADVISORY #11 for 2009-2010-3/5/10

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data. I can be reached by email (see below) if you have an important question.

Current status for 2009-10 Bloom –Due to the cool weather, predicted full bloom dates have been pushed back about one week in central and northern areas and 3 or 4 days later in southern areas. The predicted full bloom dates are 19-21 March in southern areas, 25 to 27 March in central areas and 29 to 30 March in northern areas. These dates may be pushed back one or two more days from the cold weather predicted into this weekend. The warmer weather next week should advance bud growth and full bloom will come quickly if warm weather continues after next week. In central Florida daytimes highs are projected to be above 70 degrees F through Sunday, March 14th.

Although a single intense bloom should be the norm, some blocks have little bud push while others have buds out 2 cm with the flowers clearly visible. This situation exists in Valencia blocks from Lake Alfred to Lake Placid and perhaps in all districts. A scattering of inflorescences have been observed that were near full bloom, but no healthy trees were seen with a general full bloom. With the induction levels experienced this year, I expect that most buds will produce more than one flower. Most buds appear to have leaves as well as flowers, necessary for good fruit set.

Unless unusual weather occurs, I will update these reports in two weeks, about March 19th.

FLOWER BUD INDUCTION ADVISORY #12 for 2009-2010-4/2/10

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data. I can be reached by email (see below) if you have an important question.

Summary of the 2009-10 Bloom –After excellent flower bud induction levels, flower buds began to develop around January 12-14, 2010. Initial bloom dates were predicted to be about mid-March, but cooler than normal temperatures, particularly in February and early March, delayed flower bud development. The final predicted full bloom dates were 17-23 March in southern areas, 25 to 30 March in central areas and 29 March in northern areas. The actual full bloom dates vary from block to block for a given cultivar in the same area and in general were or are 4 to 8 days later than predicted. I received a report from Ft. Pierce yesterday that 3 cultivars of mandarin hybrids were at full bloom or 1 or 2 days from that stage. This is about the same bloom stage as in Lake Alfred and several days after the predicted date of full bloom for Ft. Pierce. In Immokalee flowers were at the popcorn stage on March 16th on weak trees, and these probably were in full bloom on the predicted date of March 20th. But healthy trees were a little later. In the case of Lake Alfred bloom dates appear to be about 7 days later than the predicted date. One block of Valencia is 1-2 days from full bloom, while another block is 4-5 days from full bloom. The predicted date was March 26th. The warmer weather this week should advance growth to full bloom quickly. Again this year, the Flowering Monitor Model did not adjust well to the abnormal temperatures near bloom. On the other hand it still is only about 1 week off the adjusted predicted date. It did adjust well to the February cool temperatures, just not those in early to mid-March.

Although a single intense bloom should be the norm, the model predicted two bloom waves in Ft. Pierce. Based on the report from there it appears that the first wave, predicted for March 17th did not develop many flowers and most flowering occurred at the end of March and early April. This first wave was predicted after 894 hours, but these trees may still be stressed and required more induction than we used to consider as adequate.

As we near full bloom, a lot of inflorescences are only generative, with no leaves. Still many buds have leaves as well as flowers, necessary for good fruit set. Overall this bloom is just within the normal time range, up to April 10th, is an intense bloom similar to the 2001-2002 induction season that led to the very large 2002-2003 crop. Fortunately or unfortunately, we don’t have so many trees now. We couldn’t market that size crop with today’s weak demand. What trees we do have, if they are healthy, should produce a good crop. We have been working on a method to assess mature tree equivalents to judge how much production potential we have. We will present that data at the Florida State Horticultural Society meeting this year in Crystal River (http://www.fshs.org/) .

One downside this year was that the winter was cold and photosynthesis was less than for a normal Florida winter, so the new fruit will not start with as high of carbohydrate reserves this spring compared to past years. The current Valencia crop may be a little short on soluble solids because of this also. If your trees lost most of their leaves this winter due to freeze damage or because they are in poor health, do not expect them to set a good crop even though they have a heavy bloom.

Unless unusual weather occurs, I will only update this report one more time in June, after the May-June drop. At that time we should know if the trees are carrying a good crop as predicted.

FLOWER BUD INDUCTION ADVISORY #13 for 2009-2010-6/10/10

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data.

Summary of the 2009-10 Bloom and Fruit set–We had excellent flower bud induction levels with flower buds beginning development in mid-January after about 1250 hours of inductive temperatures in central Florida. This is 400 more hours than in the 2002-2003 flowering for the 2003-2004 bumper crop. Other production areas also had proportionately more induction.

Bloom was later than usual for recent years and generally intense as predicted from the inductive levels. Leafy bloom, which supports good fruit set, was reasonable for the intense flowering. During bloom and the fruit set period there were frequent rains and temperatures were cooler than normal, both helping fruit set. We should be in the mid to upper range of fruit numbers per mature tree equivalent.

Fortunately or unfortunately, we don’t have so many trees now. If you accurately know how many trees we have, you can make a prediction of what the crop will be.

Unless unusual weather occurs this Fall (hurricanes) or Winter (freezes), we should produce more fruit than last year’s prediction.

One last note: I am retiring on June 30th after 42 years at CREC. I am not going away and will help someone make the transition next year to providing the basic Flower Bud Induction Advisories on this CREC Website. My research program will continue with no substantial changes for at least another year.

FLOWER BUD INDUCTION ADVISORY #1 for 2008-2009-11/10/08

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Overview of flower bud induction in Florida – Citrus flower bud induction starts in the fall and usually is completed by early January. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F). A period of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be an ENSO-neutral year, average temperatures and rainfall. Under these conditions, enough hours of low temperatures below 68 degrees F. usually accumulate to induce a reasonable level of flower buds. Conditions that can interfere with good flower bud induction include: 1) several warm periods interrupt the induction process or 2) the previous crop was exceptionally high or 3) leaf loss from hurricanes or other causes (canker) was excessive and tree recovery was not complete. Two or three lead to low carbohydrate levels in developing buds which reduced their ability to become flower buds. None of these adverse conditions appear to be in play for the coming seasons flower bud induction.

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 800 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction may occur after 700 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures > 80 to 85 degrees F., can trigger growth (bud swelling) if a minimum total hours of low temperatures have accumulated (400-500 hours below 68 degrees F). Later in the winter when the accumulated cool temperature induction hours are high, fewer days and lower daytime highs (75 degrees F.) are required in a warm period to stimulate growth of buds. Weather information relative to Florida citrus flower bud development for the current and several previous year’s (back to 1998) can be obtained from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. An 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt for the next week. Find this information at: http://www.nws.noaa.gov/mdl/forecast/text/state/FL.MRF.shtml. This is an easy way to see if a warm period, which could trigger flower bud growth, is predicted for your specific area in Florida.

Some flower buds will be induced in the range of 350 to 450 accumulated hrs < 68 degrees F. Warm events just after these levels of induction result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well watered. The first situation results in multiple cohorts of flower buds developing to different bloom dates. The second condition leads to low flowering-fruit set and excessive spring vegetative growth. During the years from 1963 to 2003, multiple blooms occurred in over half of the years. Historically, the time period in which an early warm period (7-12 day) can lead to an initial low number of buds growing is roughly mid-November to mid-December. Then additional flower buds develop later resulting in multiple blooms. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is sufficient drought stress to stop growth. This water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts of cool periods. Sufficiently cool temperatures after a cold front rain will usually prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus’. Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering respectively. If the current crop is very heavy, then the greener shaded bands should be broader (require more hours for the same level of flowering). If the current crop is lighter or tree condition better, then the colored bands should be narrower as the level of potential flowering will be greater at lower total cool temperature hours. Although this representation does not appear on the working screen, recommendations (bottom text box) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process. The system is available on-line and may be accessed at: http://orb.at.ufl.edu/DISC/bloom

Weekly or bi-weekly advisories will follow this preliminary one and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

Previous responses -- In the winter of 2001-2002 following a good crop, cool temperature accumulation was very slow and low (640 hours accumulated), warm temperatures persisted and most buds started to grow by 20 December, particularly in well irrigated blocks, leading to excessive vegetative buds. This resulted in few buds remaining for a second flowering wave and a small crop occurred (2002-03 crop). By late December in the winter of 2002-2003, we had 850 hours of uninterrupted cool inductive temperatures with a low current crop on the trees. The following warm period initiated almost all the buds on all of the spring and summer flush to differentiate and bloom in early March. Still we had a fairly leafy bloom of very short duration (slightly more than 2 weeks). In spite of the high temperatures during and following bloom, an excellent fruit set occurred in all round oranges resulting in the highest October Florida citrus crop forecast by the Florida Agric. Statistical Service ever (2003-04 crop). In the winter of 2003-2004, there was good flower bud induction and reasonably good fruit setting conditions, although the heavy previous crop probably reduced flowering levels and set. Even though fruit size was small, it looked like we were headed for a 220 million box orange yield before the 2004 hurricanes significantly reduced the 2004-05 crop. Since then, we have had Hurricane Wilma in 2005, a long period of tree recovery from the 2004 and 2005 hurricanes plus tree losses from canker eradication. Until this year, flowering levels have been low and required more hours for the peak bloom to occur, probably because of continued tree recovery after the multiple hurricanes. This past year accumulated hours below 68 degrees F were more than acceptable by the second warm period (over 1000 hours) but flowering and crop per tree was still low resulting in only 166 million boxes of oranges. This low yield probably indicated that the trees still were not fully recovered from hurricane effects. Some details of the hurricane effects can be reviewed in the 11/01/2006 summary-introduction for the previous year’s flower induction cycle.

Current status for 2008-09 Winter - The light to medium crops and general tree recovery without a hurricane should lead to a flowering response next spring more typical of citrus in Florida, unless an unusual event occurs. This is supposed to be a ENSO-neutral winter with average cool temperature accumulation if warm periods do not interrupt the accumulation process. Currently, citrus locations have accumulated low temperatures < 68 degrees F of 225 to 400 hours from southern to northern areas, respectively. The next 8 days will be below average cool temperatures and another 140 to 168 hours should accumulate. Continued accumulation of cool temperatures and prevention of growth during a winter warm spell are important for a good start for 2009-10 citrus production. Therefore, start to monitor irrigation amounts so drought stress can occur if a warm period occurs between November 15 and Christmas, depending on the rate of cool temperature accumulation and reaching an acceptable level of over 750-800 hours. Prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory.

FLOWER BUD INDUCTION ADVISORY #2 for 2008-2009-11/24/08

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data

Current status for 2008-09 fall-winter – Improved tree condition of non-HLB affected trees since the 2004-05 hurricanes should be promising for good flowering next spring if cool weather accumulation continues. Through November 23rd, citrus locations had accumulated low temperatures (< 68 degrees F) of 400 to 600 hours from southern to most northern areas, respectively. The next 8 day forecast from NOAA calls for relatively cool temperatures and another 100 to 120 hours below 68 degrees F should accumulate. The most northern FAWN site for citrus has now accumulated 622 hours and by next week this total should exceed 700 hours. The warmer southern areas will have about 500 hours. These values are ahead of last year at this time by over 150 hours, but last year was about 100 hours below the previous year.

If moderately cool weather continues for three more weeks, 2 weeks into December, the accumulation of cool temperatures in the southern areas would be marginally acceptable for an economic crop and acceptable (800 hours below 68 degrees F) for all other citrus areas in Florida. At the same time prevention of growth during a winter warm spell is very important over the next 3 to 4 weeks in order to prevent initiation of bud growth too early. Cool temperature accumulation is now at the level that bud growth of terminal buds could be easily initiated if a warm period occurred. Therefore, continue to monitor and reduce irrigation amounts so drought stress can easily and rapidly occur if a warm period occurs between now and mid-December to Christmas. Maintenance of water stress during this period also is an alternative to having sufficient cool temperatures for flower bud induction. In recent studies, field trees held under some water stress had more flowers than trees irrigated during the winter.

At the very least, prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory. See last week’s background advisory for additional irrigation details.

The other side of winter conditions is concern for a freeze. In this Neutral ENSO winter, freezes are more likely. So far the early and continued cool weather should provide reasonable cold hardiness in the trees. The Jet Stream flow is still mostly lateral from West to East across the southern half of the US so rapid Arctic Express cold air movement into Florida is not likely. Check the Weather Underground on the CREC Weather links for easy access to Jet Stream patterns.

There are two useful Websites to follow weather forecasts. The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click. Alternative, an 8 day forecast can be viewed by going to https://crec.ifas.ufl.edu/ and click on resources> weather> 8-day forecast. Remember during this critical period to view FAWN, use the on-line monitor site provided in the first advisory and the NOAA 8 day forecast. In order to prevent bud growth, trees should be slightly stressed if a warm period (7-10 days with maximum temperatures above 85 degrees F.) is predicted.

FLOWER BUD INDUCTION ADVISORY #3 for 2008-2009-12/16/08

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data

Current status for 2008-09 fall-winter – Cool weather accumulation has continued at a good rate to the point that the induced buds are now very easy to stimulate into flower bud growth and differentiation. The flowering monitor program indicates that the easy to induce buds have started to differentiate in the more northern locations (Avalon at 800 hours and Umatilla at 820 hours). Other areas of the state may follow suit if temperature highs stay at 80 degrees F or higher for several days this week. Through December 16th, citrus locations had accumulated low temperatures (< 68 degrees F) of 720 to 1000 hours from southern to the most northern areas, respectively. The next 8 day forecast from NOAA calls for relatively cool temperatures and another 80 to 100 hours below 68 degrees F should accumulate. The current values are acceptable for commercial crops in all areas except Ft. Pierce and more southern East Coast locations. In another 8 days, the East Coast area should have an acceptable level of cool temperature accumulation also.

The northern areas have projected first bloom wave dates of February 2nd (Avalon) and February 6th (Umatilla) which, if correct, are very early and would put the flowers at risk to a potential frost. Since the accumulated cool temperatures are in the 800s, the first wave of flowers should be the major wave for all of the citrus production areas. During the past 3 years the trees have not responded by having their major bloom from this many hours of cool temperature accumulation. If they do respond this year with the major bloom from the first initiation-differentiation wave, then the trees have probably finally returned to normal after the 2004-05 hurricanes.

The cool temperature accumulation is so good that I would advise trying to minimize growth through moderate drought maintenance rather than applying urea or phosphorous acid sprays to enhance flowering. This is the most economical option as it saves spray and materials cost as well as some irrigation costs. In all cases where the current crop is low to moderate, the return flowering should be very good without help. Even if the current crop is a fairly heavy another two weeks should put induction levels at a high level, exceeding 1000 hours.

It is not advisable to start pushing growth of the trees as 1. An early February bloom is not desirable, and 2. Irrigating might reduce the cold hardiness level which should still be fairly good with the consistent cool temperatures experienced so far this fall and winter.

The freeze hazard will be fairly high from now until January 15th. In this Neutral ENSO winter, freezes are more likely. The Jet Stream flow is still mostly horizontal from West to East across the southern two-thirds of the US so rapid Arctic Express cold air movement into Florida is not likely. Check the Weather Underground on the CREC Weather links for easy access to Jet Stream patterns and watch it carefully over the next month for any significant change to a southern dip that can easily lead to freezing temperatures in Florida.

There are two useful Websites to follow weather forecasts. The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click. Alternative, an 8 day forecast can be viewed by going to https://crec.ifas.ufl.edu/ and click on resources> weather> 8-day forecast. Remember during this critical freeze period to view FAWN, use the on-line monitor site provided in the first advisory and the NOAA 8 day forecast and watch the Jet Stream pattern. In order to prevent bud growth now that trees are at a high level of induction, trees should be slightly stressed if a warm period (5-7 days with maximum temperatures above 80 degrees F.) is predicted.

FLOWER BUD INDUCTION ADVISORY #4 for 2008-2009-1/5/09

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data

Current status for 2008-09 fall-winter – Cool weather accumulation continued at a good rate to the point that the induced buds were easy to stimulate into flower bud growth and differentiation. Sufficient warm weather occurred before Christmas in December for bud differentiation to start in all districts. The flowering monitor program indicates that these easy to induce buds had started to differentiate from 2 December in the more northern locations (Avalon at 800 hours and Umatilla at 820 hours) until about 11 December in southern areas . Many areas of the state now have a second wave of bud growth with the start of that differentiation occurring just before Christmas. Citrus locations had accumulated low temperatures (< 68 degrees F) of 695 to 1000 hours from southern to the most northern areas, respectively, when the first wave of differentiation started. For Central to northern areas the second wave of buds had over 1000 hours of cool induction at the time of differentiation. The southern areas should have a second wave of flower bud differentiation starting shortly. The current values of flower bud induction are very acceptable for commercial crops in all areas.

The projected first bloom wave dates are from week one in February (Ft. Pierce, Ona, and Umatilla) to the second week in February for all other areas except Lake Alfred and Avalon. The ‘flowering monitor system’ projects full bloom dates of 23 to 26 January for these two locations and bud swell is evident at Lake Alfred, but I don’t see any reason for bloom this early and assume that bloom at these two areas should fall in line with other areas to their north and south. Therefore bloom at these locations also should be the first week of February. Still this would be an early bloom and leave the trees very susceptible to a frost. So far the Jet Stream pattern is favorable for minimizing our risk to a freeze, but there is a deep trough in the Jet stream over the Pacific Northwest that we should watch carefully to be sure it does not slide to the east (http://www.wunderground.com/US/Region/US/JetStream.shtml).

Since the accumulated cool temperatures for the start of the first differentiation are in the 700-800 range, the first wave of flowers should be the major wave for all of the citrus production areas. However during the past 3 years (since the 2004 hurricanes) the trees have not responded by having their major bloom with only this many hours of cool temperature accumulation. If they do respond this year with the major bloom from the first initiation-differentiation wave, then the trees have probably finally returned to normal after the 2004-05 hurricanes.

The cool temperature accumulation is very good, but I would advise trying to minimize growth through moderate drought maintenance rather than applying urea or phosphorous acid sprays to enhance flowering. The bud development is past when these sprays should help and maintaining some drought stress is the most economical option as it saves spray and materials cost as well as some irrigation costs. In all cases where the current crop is low to moderate, the return flowering should be very good without help. Even if the current crop is fairly heavy the total induction level is high, exceeding 1000 hours. Further, it is not advisable to start pushing growth of the trees as 1) an early February bloom is not desirable due to frost hazard and it would lead to early fruit maturation and poorer fruit quality, and 2) irrigating might reduce the cold hardiness level which should still be fairly good now if a freeze were to occur in the next two weeks.

The freeze hazard is usually fairly high from now until January 20th. In a Neutral ENSO winter like this year, freezes are more likely. As stated earlier, the Jet Stream flow is still mostly horizontal from West to East across the southern two-thirds of the USA but rapid Arctic Express cold air movement into Florida could occur if the Jet Stream trough moves to the eastern USA.

There are two useful Websites to follow weather forecasts. The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click. Alternative, an 8 day forecast can be viewed by going to https://crec.ifas.ufl.edu/ and click on resources> weather> 8-day forecast. Remember during this critical freeze period to view FAWN, use the on-line monitor site provided in the first advisory and the NOAA 8 day forecast and watch the Jet Stream pattern. In order to prevent or delay bud growth now that trees are at a high level of induction and have some bud differentiation, trees should be slightly stressed if a warm period (5-7 days with maximum temperatures above 80 degrees F.) is predicted.

FLOWER BUD INDUCTION ADVISORY #5 for 2008-2009-1/15/09

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data. This advisory was a quick update since cold weather was predicted for the weekend

Freeze potential according to Albrigo – The Jet Stream trough did move east from the Pacific Northwest and was bringing cold temperatures deep into Texas. However as of today, the Jet Stream is turning East in North Texas and Oklahoma, maybe the Gators scared it north. Warmer air is being drawn from the Gulf and lowest temperatures are now projected to be above the freezing point in most of the citrus growing area of Florida

Current status for 2008-09 fall-winter – We now have up to 3 flowering waves predicted. Both in Lake Placid and Lake Alfred, there is a light wave of flower buds at pinhead stage. There was more in Lake Placid, and they were more advanced than at Lake Alfred as of yesterday. This first wave is much lighter than would be expected for 700 to 800 hours of cool temperatures so trees may still be behind their condition prior to the hurricanes. We do now have a second wave projected in the south with 900 hours of induction and up to 3 waves projected from Sebring north with 1000 and 1200 hours respectively. The first wave on most trees I have seen does not look significant and the major flowering should be expected in the later waves, which should come in mid-February and early March. The dates of full bloom may be delayed if cool weather continues.

FLOWER BUD INDUCTION ADVISORY #6 for 2008-2009-3/6/09

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data.

Current status for the 2008-09 bloom and the 2009-10 crop – The 3 flowering waves have or are occurring as predicted. However, the bloom dates were set back significantly by the relatively continuous cooler weather in January and February. We now should have the major bloom waves the first two weeks of March and third week of March for Central Ridge, near the normal bloom date in recent years. We have noticed that if cool weather occurs after the flower buds are growing and showing some extension the dates of full bloom are delayed. Further development essentially stops until warmer temperatures occur again. The flowering monitor system does not reflect this late cold weather effect.

The first wave of flower buds was very light and these flowers froze in colder areas. This flower loss will not have any impact on crop potential as flower numbers were very low. However, on trees that lost most of their mature leaves from freeze damage, heavier new vegetative flushes will compete with flower set of the later bloom waves resulting in a decrease in fruit set. Hopefully, the flowering intensity of the second and thirds flowering waves will be heavy enough to still have reasonable fruit sets. The second wave, with 900 to 1000 hours of cool temperatures, is blooming now (white pinhead to popcorn in the Central Ridge. Often this wave is mostly flowers (generative) with few leaves associated with the inflorescences. There appears to be much better leaf development in the third wave of developing flower buds on trees that I have seen in Lake Placid, Lake Wales and Lake Alfred. In our area, these flowers are at the small, green pinhead stage. The lack of leafy bloom in the second wave will depress fruit set, but the more leafy third wave is often substantial in numbers and should have a good set. Between these two flowering waves it looks like flowering intensity will be high enough to provide at least an average crop. After the fruit set period, by mid-May, the fruit set can be evaluated and a final advisory will be posted.

Freeze effects on bloom – A few things to remember about freezes and flowering: Freezes do not enhance flowering intensity, in fact temperatures near freezing, probably up to near 40 degrees F, are too cold to add to the flowering intensity. Developing more flowering intensity is a slow process and requires substantial hours of cool temperatures. If leaves quickly drop off after a freeze, then little shoot damage has occurred and flowering will usually be normal. If leaves dry up and remain attached to the twig, wood (cambial) damage has occurred and flower buds will not develop normally, usually die after initial push. It usually takes more than 6 weeks to actually see how much wood damage occurred.

Watch these next two flowering waves, particularly the third wave for its intensity and leafiness. If it is substantial in your blocks and the weather during bloom is good for bee activity, expect a good crop. An advisory should be posted about mid-May to summarize our crop potential.

FLOWER BUD INDUCTION ADVISORY #7 for 2008-2009-6/12/09

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data

Summary for the 2008-09 bloom and the 2009-10 crop – The 3 flowering waves occurred as predicted. However, the bloom dates were set back significantly by the relatively continuous cooler weather in January and February. The major bloom waves were the last two, with the last occurring the third to fourth week of March for the Central Ridge, similar bloom dates to last year. We have noticed that if cool weather occurs after the flower buds are expanding the dates of full bloom are delayed. Further development essentially stops until warmer temperatures occur again. The flowering monitor system does not reflect this late cold weather effect.

The first wave of flower buds was very light and these flowers froze in colder areas. This flower loss did not have any impact on crop potential as flower numbers were very low. However, on trees that lost most of their mature leaves from freeze damage, heavier new vegetative flushes competed with flower set of the later bloom waves resulting in a decrease in fruit set. However, there were not many trees with heavy leaf loss so this situation is only important if it was your trees. Hopefully, the flowering intensity of the second and thirds flowering waves was heavy enough to still have reasonable fruit set on these trees.

The second wave of flowers, after 900 to 1000 hours of cool temperature induction, was mostly generative inflorescences with few leaves associated with the flowers. There was much better leaf development in the third wave of developing flower buds and this had the most intense flowering. The third wave responded to 1214 hours (Lake Alfred) of inductive temperatures. Therefore theses buds were difficult to induce which accounts for their higher leaf to flower ratio. This leafy third wave should have been responsible for most of the fruit set. From the second and third flowering waves total flowering intensity was high and sufficient to provide at least an average crop.

Weather was relatively cool during flowering and initial fruit set (low 80s to 88 in Immokalee from 18 March to 10 April) which delayed drop of the young fruit. This resulted in a heavier drop during the May-June drop period. The weather in late April and early May was back to normal with near 90 to low to mid-90s the first week of May. The May-June drop occurred under normal conditions of hot, dry weather. The last part of this drop wave occurred under an unusually early and long rainy period, but this rain probably was too late to alter the amount of drop very much. Still, it no doubt was beneficial, particularly for good early fruit growth. Some Indian River areas had difficulty meeting irrigation needs, which may have reduced fruit set on trees in these areas..

Overall, we should have at least a normal crop load for the trees we have left. The question is how many mature trees do we have left, particularly in the southern third of the industry where huanglongbing took out larger numbers of trees this past year. This year HLB may have a significant effect on industry-wide yield. In my opinion, minus the tree losses, we should have a total crop similar to last year.

FLOWER BUD INDUCTION ADVISORY #7 for 2008-2009-6/12/09

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data

Summary for the 2008-09 bloom and the 2009-10 crop – The 3 flowering waves occurred as predicted. However, the bloom dates were set back significantly by the relatively continuous cooler weather in January and February. The major bloom waves were the last two, with the last occurring the third to fourth week of March for the Central Ridge, similar bloom dates to last year. We have noticed that if cool weather occurs after the flower buds are expanding the dates of full bloom are delayed. Further development essentially stops until warmer temperatures occur again. The flowering monitor system does not reflect this late cold weather effect.

The first wave of flower buds was very light and these flowers froze in colder areas. This flower loss did not have any impact on crop potential as flower numbers were very low. However, on trees that lost most of their mature leaves from freeze damage, heavier new vegetative flushes competed with flower set of the later bloom waves resulting in a decrease in fruit set. However, there were not many trees with heavy leaf loss so this situation is only important if it was your trees. Hopefully, the flowering intensity of the second and thirds flowering waves was heavy enough to still have reasonable fruit set on these trees.

The second wave of flowers, after 900 to 1000 hours of cool temperature induction, was mostly generative inflorescences with few leaves associated with the flowers. There was much better leaf development in the third wave of developing flower buds and this had the most intense flowering. The third wave responded to 1214 hours (Lake Alfred) of inductive temperatures. Therefore theses buds were difficult to induce which accounts for their higher leaf to flower ratio. This leafy third wave should have been responsible for most of the fruit set. From the second and third flowering waves total flowering intensity was high and sufficient to provide at least an average crop.

Weather was relatively cool during flowering and initial fruit set (low 80s to 88 in Immokalee from 18 March to 10 April) which delayed drop of the young fruit. This resulted in a heavier drop during the May-June drop period. The weather in late April and early May was back to normal with near 90 to low to mid-90s the first week of May. The May-June drop occurred under normal conditions of hot, dry weather. The last part of this drop wave occurred under an unusually early and long rainy period, but this rain probably was too late to alter the amount of drop very much. Still, it no doubt was beneficial, particularly for good early fruit growth. Some Indian River areas had difficulty meeting irrigation needs, which may have reduced fruit set on trees in these areas..

Overall, we should have at least a normal crop load for the trees we have left. The question is how many mature trees do we have left, particularly in the southern third of the industry where huanglongbing took out larger numbers of trees this past year. This year HLB may have a significant effect on industry-wide yield. In my opinion, minus the tree losses, we should have a total crop similar to last year.

FLOWER BUD INDUCTION ADVISORY #1 for 2007-2008-11/01/07

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Overview of flower bud induction in Florida – Citrus flower bud induction starts in the fall and usually is completed by early January. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F). A period of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be a La Nina year, higher than average temperatures and lower than average rainfall. Even under these conditions, enough hours of low temperatures below 68 degrees F. usually accumulate to induce a reasonable level of flower buds. Conditions that can interfere with good flower bud induction include: 1) several warm periods interrupt the induction process or 2) the previous crop was exceptionally high or 3) leaf loss from hurricanes or other causes (canker) was excessive and tree recovery was not complete. Two or three lead to low carbohydrate levels in developing buds which reduced their ability to become flower buds.

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 800 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction may occur after 700 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures > 80 to 85 degrees F., can trigger growth (bud swelling) if a minimum total hours of low temperatures have accumulated (400-500 hours below 68 degrees F). Later in the winter when the accumulated cool temperature induction hours are high, fewer days and lower daytime highs (75 degrees F.) are required in a warm period to stimulate growth of buds. Weather information relative to Florida citrus flower bud development for the current and several previous year’s (back to 1998) can be obtained from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. An 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt for the next week. Find this information at: http://www.nws.noaa.gov/mdl/forecast/text/state/FL.MRF.shtml. This is the easiest way to see if a warm period, which could trigger flower bud growth, is predicted.

Some flower buds will be induced in the range of 300 to 450 accumulated hrs < 68 degrees F. Warm events just after these levels of induction result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well watered. The first situation results in multiple cohorts of flower buds developing to different bloom dates. The second condition leads to low flowering-fruit set and excessive spring vegetative growth. During the years from 1963 to 2003, multiple blooms occurred in over half of the years. Historically, the time period in which an early warm period (7-12 day) can lead to an initial low number of buds growing is roughly mid-November to mid-December. Then additional flower buds develop later resulting in multiple blooms. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is sufficient drought stress to stop growth. This water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts of cool periods. Sufficiently cool temperatures will prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus’. Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering respectively. If the current crop is very heavy, then the greener shaded bands should be broader (require more hours for the same level of flowering). If the current crop is lighter or tree condition better, then the bands should be narrower as the level of potential flowering would be greater at lower total cool temperature hours. Although this representation does not appear on the working screen, recommendations (bottom text box) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process. The system is available on-line and may be accessed at: http://orb.at.ufl.edu/DISC/bloom.

Weekly or bi-weekly advisories will follow this preliminary one and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

Previous responses – In the winter of 2001-2002 following a good crop, cool temperature accumulation was very slow and low (640 hours accumulated), warm temperatures persisted and most buds started to grow by 20 December, particularly in well irrigated blocks, leading to excessive vegetative buds. This resulted in few buds remaining for a second flowering wave and a small crop occurred (2002-03 crop). By late December in the winter of 2002-2003, we had 850 hours of uninterrupted cool inductive temperatures with a low current crop on the trees. The following warm period initiated almost all the buds on all of the spring and summer flush to differentiate and bloom in early March. Still we had a fairly leafy bloom of very short duration (slightly more than 2 weeks). In spite of the high temperatures during and following bloom, an excellent fruit set occurred in all round oranges resulting in the highest October Florida citrus crop forecast by the Florida Agric. Statistical Service ever (2003-04 crop). In the winter of 2003-2004, there was good flower bud induction and reasonably good fruit setting conditions, although the heavy previous crop probably reduced flowering levels and set. Even though fruit size was small, it looked like we were headed for a 220 million box orange yield before the 2004 hurricanes significantly reduced the 2004-05 crop. Since then, we have had Hurricane Wilma in 2005, a long period of tree recovery from the 2004 and 2005 hurricanes plus tree losses from canker eradication. Until this year, flowering levels have been low probably because of continued tree recovery after the multiple hurricanes. This past year accumulated hours below 68 degrees F were more than acceptable by the second warm period (over 1000 hours) but it was not until the third warm period with over 1150 hours accumulated that the major flowering wave was triggered. This high level probably indicated that the trees still were not fully recovered from hurricane effects. Some details of the hurricane effects can be reviewed in the 11/01/2006 summary-introduction for last year’s flower induction cycle.

Current status for 2007-08 winter - The heavier crop and general tree recovery without a hurricane should lead to average flowering next spring, unless an unusual event occurs. Although this is supposed to be a La Nina winter with warmer and dryer than normal weather, average cool temperature accumulation if warm periods do not interrupt the accumulation process. Currently, citrus locations have accumulated low temperatures < 68 degrees F of 45 to 150 hours from southern to northern areas, respectively. The next 8 days will be below average cool temperatures and another 140 to 168 hours should accumulate. Continued accumulation of cool temperatures and prevention of growth during a winter warm spell are important for a good start for the 2007-08 citrus production. Therefore, start to monitor irrigation amounts so drought stress can occur if a warm period occurs between November 15 and Christmas, depending on the rate of cool temperature accumulation and reaching an acceptable level of 800 hours. Prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory.

FLOWER BUD INDUCTION ADVISORY #2 for 2007-2008-11/21/07

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data.

Current status for 2007-08 winter - The general continued tree recovery since the 2004-05 hurricanes should be promising for good flowering next spring if cool weather accumulation is favorable. Although this is supposed to be a La Nina winter with warmer and dryer than normal weather, average or better cool temperature accumulation can occur if warm periods do not interrupt the accumulation process. Through November 20th, citrus locations had accumulated low temperatures < 68 degrees F of 225 to 375 hours from southern to most northern areas, respectively. The next 8 day forecast calls for relatively cool temperatures and another 100 to 140 hours < 68 degrees F should accumulate. The most northern FAWN site has now accumulated 380 hours and by next week this total should exceed 530 hours. The warmer southern areas will have about 340 hours. These values are behind last year at this time by about 100 hours.

Continued accumulation of cool temperatures and prevention of growth during a winter warm spell are important for a good start for the 2007-08 citrus production. After next week we could have bud growth initiated if a warm period occurred as these values will approach those needed to have buds that are easy to stimulate into growth. Therefore, start to monitor and reduce irrigation amounts so drought stress can occur if a warm period occurs between now and Christmas. With the better crop this year, an acceptable level of cool temperature accumulation would probably be at least 800 hours. Maintenance of water stress during this period is an alternative to having sufficient cool temperatures for flower bud induction. The last two years field trees held under some water stress had more flowers than trees irrigated during the winter. A La Nina year favors the ability to maintain water stress as it should be dryer than normal.

At the very least, prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory. See last week’s background advisory for irrigation details. There are two useful Websites to follow weather forecasts. The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click. Alternative, an 8 day forecast can be viewed by going to https://crec.ifas.ufl.edu/ and click on resources> weather> 8-day forecast. Remember during this critical period to view FAWN, use the on-line monitor site provided in the first advisory and the NOAA 8 day forecast. Trees should be slightly stressed if a warm period is predicted (7-10 days with maximum temperatures above 85 degrees F.) in order to prevent bud growth.

FLOWER BUD INDUCTION ADVISORY #3 for 2007-2008-12/05/07

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data

Current status for 2007-08 Winter - Although this is supposed to be a La Nina winter with warmer and dryer than normal weather, average or better cool temperature accumulation can occur if warm periods do not interrupt the accumulation process. Unfortunately so far, this year is behaving like an average La Nina winter. Through December 4th, citrus locations had accumulated low temperatures < 68 degrees F of 340 to 550 hours from southern to most northern areas, respectively. The next 8 day forecast calls for cool nights, but moderate daytime temperatures with another 100 to 140 hours < 68 degrees F accumulating. The most northern FAWN may accumulate another 150 hours by next week and exceed 700 hours. The warmer southern areas will have about 450 hours. On 12 December, these values will be further behind last year by about 160 to 300 hours from the southern to northern citrus areas.

Even though cool temperature accumulation is lower than last year, the trees will have reached induction levels at the end of this cool period that make the buds very vulnerable to stimulation of bud growth by a warm period. A week with daytime highs in the mid-80s would probably promote growth of the terminal-most 2 to 3 buds. If that next warm period comes before New Year’s, it is very important for soil moisture to be low so that bud growth is suppressed by mild drought conditions.

Therefore, you should be monitoring and reducing irrigation amounts so drought stress can occur if a warm period is predicted and occurs between now and Christmas. Since the next few days will be relatively cool, be careful not to over water. The trees don’t need much soil moisture at this time. With the better crop this year, an acceptable level of cool temperature accumulation would probably be at least 800 hours. The trees are not likely to reach that level of cool temperature induction. Maintenance of water stress during this period is an alternative to having sufficient cool temperatures for flower bud induction. The last two years field trees held under some water stress (no irrigation) had more flowers than trees irrigated during the winter. A La Nina year favors the ability to maintain water stress as it should be dryer than normal. If there is no rain, you may need to bump soil moisture up periodically with light irrigations. Do not apply normal, full volume irrigations until it is time to purposely stimulate bud growth, sometime in January at the earliest.

By now you should have groves with relatively dry soils in the lower rooting depths from withholding heavier irrigations. Keep track of induction hours in your area and watch for the next advisory. See the initial background advisory for more irrigation details. There are two useful Websites to follow weather forecasts. The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click. Alternative, an 8 day forecast can be viewed by going to https://crec.ifas.ufl.edu/ and click on resources> weather> 8-day forecast. Trees should be slightly stressed if a warm period is predicted (7-10 days with maximum temperatures above 85 degrees F.) in order to minimize bud growth.

In the next advisory we will review the use of foliar urea or phosphorous salts (PO3) at the beginning of a warm time period in order to enhance flowering intensity when cool temperature induction is inadequate. This may be very useful this year, particularly in southern regions, if rains raise soil moisture levels at lower rooting depths and warm weather occurs before Christmas. The background and last year’s advisory may be reviewed for more information.

FLOWER BUD INDUCTION ADVISORY #4 for 2007-2008-12/20/07

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data

Current status for 2007-08 Winter - This is a La Nina winter with warmer and dryer than normal weather, and so far, this year is behaving like an average La Nina winter. Through December 19th, citrus locations had accumulated low temperatures < 68 degrees F of 490 to 760 hours from southern to most northern areas, respectively. The next 8 day forecast calls for cool nights, but moderate daytime temperatures with another 80 to 110 hours < 68 degrees F accumulating. The most northern FAWN may reach a satisfactory 850 hours of temperatures < 68 degrees F. The warmer southern areas will only have about 575 hours of temperatures < 68 degrees F shortly after Christmas. This is probably 150 to 200 hours short of a good minimum for a satisfactory flowering level on trees with a good current crop.

Although most areas received rainfall this past week, FAWN data indicates that only northern areas reportedly received soil saturating amounts. The cool temperatures this week should have allowed soil drying so that drought conditions may exist again when a warm period starts. It is advisable to continue dry soil conditions for at least another 2 to 3 weeks while cool inductions temperatures continue to accumulate. If a warm period (7 days above 83-85 degrees F) occurs before then with adequate soil moisture for growth, growers should consider applying either 53 to 60 lbs of foliar urea/acre in 80 to 125 gal of water, or a PO3 product at 3 pints to 2 quarts per acre depending on which product is used (60 % P (3pts) or if 26 % P (2 qts) product). This should be applied in the first 2 to 3 days at the beginning of the warm period..

See the initial background advisory for more irrigation details. There are two useful Websites to follow weather forecasts. The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click. Alternative, an 8 day forecast can be viewed by going to https://crec.ifas.ufl.edu/ and click on resources> weather> 8-day forecast. Trees should be slightly stressed if a warm period is predicted (7-10 days with maximum temperatures above 85 degrees F.) in order to minimize bud growth. This practice should continue if possible until we reach 750 to 800 hours below 68 degrees F or a warm period starts after a saturating rain at which time urea of PO3 should be applied to enhance the level of flower induction.

Keep track of induction hours in your area. Because of the holidays, the next advisory will not be posted until after New Year’s Day.

FLOWER BUD INDUCTION ADVISORY #5 for 2007-2008-1/02/08

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data.

Will favorable weather last for two more weeks? If so, we will have a decent flower bud induction period for next year’s crop.

Current status for 2007-08 Winter –This is a La Nina winter with warmer and dryer than normal weather, and so far, this year is behaving like an average La Nina winter. The good aspect is that no prolonged warm period has occurred and therefore we are still accumulating flower bud induction. Through December 30th, citrus locations had accumulated low temperatures < 68 degrees F of 615 to 935 hours from southern to most northern areas, respectively. The next 8 day forecast calls for cool nights, a possible freeze but moderate daytime temperatures with another 95 to 120 hours < 68 degrees F accumulating. The most northern areas will exceed 1000 hours of temperatures < 68 degrees F. The warmer southern areas will have about 720 hours of temperatures < 68 degrees F by next week. This is probably 100 hours short of a good induction level for satisfactory flowering on trees with a good current crop.

Perhaps of some interest is that according to the Citrus Flowering Monitor System, Citra has two flowering waves developing for mid and late February blooms. This clearly indicates that other areas will have trees responding to moderate temperatures with bud growth in the near future. Buds will probably begin to push if 4 or 5 days in the low 80s occur.

Some areas received rainfall this past week, and more may occur on the cold front approaching now. The cool temperatures this week should allow soil drying before a warm period starts. It appears that we can get another week of induction after this coming week, particularly if no additional rains occur. If however a warm period (5 to 7 days above 80 degrees F) starts early next week with adequate soil moisture for growth, growers in the more southern regions should consider applying either 53 to 60 lbs of foliar urea/acre in 80 to 125 gal of water, or a PO3 product at 3 pints to 2 quarts per acre depending on which product is used (60 % P (3pts) or if 26 % P (2qts) product). These sprays should be applied in the first 2 to 3 days at the beginning of the warm period.

As to the freeze potential for tomorrow, conditions are favorable for temperatures to be above those predicted by NOAA. There is only a moderate dip in the Jet Stream, the dip is west of the Eastern states, but the temperatures over southern Texas are cold. There is a northern draft on the eastern side that may draw warmer temperatures out of the Gulf. That could also bring clouds to help. Maybe this is just looking for the best hope for high 20s to low 30s in the citrus belt, but watch the Jet Stream and today’s highs!

There are two useful Websites to follow weather forecasts. The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click. Alternatively, an 8 day forecast can be viewed by going to https://crec.ifas.ufl.edu/ and click on resources> weather> 8-day forecast. A link to Weather Underground is also available. Trees should be slightly water stressed if a warm period is predicted (now 5-7 days with maximum temperatures above 80 degrees F.) in order to minimize bud growth. This practice should continue if possible until we reach 750 to 800 hours below 68 degrees F or a warm period starts after a saturating rain at which time urea or PO3 should be applied to enhance the level of flower induction.

If flower bud growth were to start in early January, we could expect a March 1st bloom. If you have some interest in having a later bloom, this can be accomplished if you can maintain some drought stress until late January, past the 20th. This of course depends on rainfall and temperatures, but would bring about a late March bloom with more flowers and a later maturation of the crop. Think about it for some Valencia blocks.

FLOWER BUD INDUCTION ADVISORY #6 for 2007-2008-1/8/08

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Currently, all central to northern citrus areas have flower buds initiated and growing. The flowering Monitor System indicates this growth started about 20-22 December and the projected bloom dates for this first wave of flowers is about February 28 to 2 March if normal or warmer weather continues. This first wave was induced at about 800+ accumulated hours below 68 degrees F from Sebring to northern districts. Another 200 hours has accumulated and a second wave of buds will be initiated to flower shortly.

For Immokalee and Ft. Pierce the model does not indicate that bud growth has started, but I expect bud growth initiation will start this week. Currently trees have been exposed to 730 to 760 hours of inductive temperatures.

In these areas with low total induction, trees, particularly with a heavy crop, may benefit from a spray of urea or PO3. Review the last advisory for more information. These sprays should be applied at temperature near or above 70 degrees F. and within the next week.

FLOWER BUD INDUCTION ADVISORY #7 for 2007-2008-1/18/08

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Currently, all central to northern citrus areas have flower buds initiated and growing. Southern areas such as Ft. Pierce and Immokalee probably have bud growth also, but the Flowering Monitor System does not indicate that this has happen, even though there are now 880 to over 900 hours below 68 degrees F in those areas. The Flowering Monitor System indicates this bud growth started about 20-22 December in most areas and the projected bloom dates for this first wave of flowers is from February 22 to 27 if normal or warmer weather continues. This first wave was induced at about 640 to 800+ accumulated hours below 68 degrees F from Sebring to northern districts. Another 200 hours has accumulated and a second wave of buds is initiated, and they should reach peak flowering March 11 to 14th.

Trees, particularly with a heavy crop and in areas with low total induction, , may still benefit from a spray of urea or PO3,but that time will probably be past one week after the next cold front goes by. Review the 5th advisory for more information. These sprays should be applied at temperatures above 70 degrees F.

Some blocks over-flower and set poorly. Some Valencia selections have this problem, and mandarin blocks with a light crop also are good candidates for a spray of 10 ppm GA3 at 125 gal/acre. The best timing for this spray is probably the end of next week if temperatures warm up to above 70 degrees F.

FLOWER BUD INDUCTION ADVISORY #8 for 2007-2008-2/11/08

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Currently, all citrus areas have flower buds initiated and growing. Southern areas such as Ft. Pierce and Immokalee have bud growth that started at 830 to 840 hours below 68 degrees F. Most areas had two waves of bud break and the second usually started at about 1000 hours. The Flowering Monitor System indicates this bud growth started about 22 December to early January in most areas and the projected bloom dates for this first wave of flowers is from February 27 to early March for most areas. The second wave is projected for mid-March. The bloom dates have shifted forward about 6 days from the model projections made soon after bud differentiation started. Data for Avalon appears to be incorrect for the bloom dates as projected for now and the second in late February. The bloom projection lines are also out of proper alignment.

It is now time to ride out flower bud development and note when peak blooms do occur in relationship to the projections. Stressed limbs and trees, notably HLB affected trees, may be in full bloom. Trees with easily seen flowering are suspect for stress problems. Healthy trees with a reasonable crop are showing a few pinhead inflorescences. Navels, other oranges, grapefruit and finally mandarins are advancing in that order towards full bloom.

Although most trees had good canopy recovery last spring, they may have still been affected by the hurricanes since in most cases the major bloom did not occur until the last flowering wave, after 1150 hours of inductive temperatures. The first (almost no flowers) and second (light flowering) waves occurred after 800 and 1000 hrs of inductive temperatures, respectively. In previous years, we would have expected most of the flowering to occur in the first two waves, not essentially all in the third.

Hopefully, flowering waves will be back to normal with the first two waves this year having significant flower numbers from the mid-800 to 1000 hours of inductive temperatures. You should watch these flowering waves to see if they both have significant numbers of flowers develop. If they do, the result should be good flowering levels for all trees except those that had a very heavy crop this harvest season. There have been additional cool hours, so all is not lost if the first two waves do not show normal behavior.

If we haven’t lost too many trees to diseases this year and tree health continues to improve, the next crop could exceed this season’s. Unfortunately, many blocks in the south may have lost more than 10 % of their trees to HLB. I’ll try to assess tree numbers, flower numbers and potential crop next advisory in late February, about the time projected for the initial bloom.

FLOWER BUD INDUCTION ADVISORY #9 for 2007-2008-3/4/08

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Currently, the flowering process is underway. In most cases, it appears that the first wave of flowers is fairly light as it was last year. It is also the result of about the same level of cool temperature induction as last year (830 to 840 hours below 68 degrees F). There is considerable tree to tree variation and the exact date of this wave being in full bloom is difficult to judge. It does appear that it occurred in February but maybe not as early as the Flowering Monitor Program was predicting in early February. However, in January the prediction was for the last week of February. The second wave of flowering buds is much larger and the differentiation of this group of buds started after 1015-1020 hours of cool induction. The full bloom date of this second wave is projected for the end of this week. This flowering wave should make a reasonable crop from observations locally, in Sebring and grower reports.

There is a possible 3rd wave to come at the end of March to early April. If this materializes, it will be from about 1200 hours of cool induction. This would be about the level that led to the heaviest bloom last year. From what I see, I think that most of the buds are pushing and this possible last wave will not be very strong and maybe will occur only on some trees.

It is hard to believe that there may still be a carryover effect from the hurricanes but at 830 inductive temperatures hours again there is only a fairly light bloom. In previous years, we would have expected stronger flowering at this induction level. At least this year, the second wave of flowers is strong enough apparently to minimize heavy flowering in a third wave of flowering buds..

In 2 weeks we can look at a final summary of the flowering this season and assess our crop potential.

FLOWER BUD INDUCTION ADVISORY #10 for 2007-2008-3/27/08

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Although the flowering process is almost over, there are still some popcorn flowers and occasionally even a new inflorescence at pinhead stage. The date of full bloom has turned out to be later than projected by the ‘Citrus Flowering Monitor’ system’. I would say full bloom date was a week later than those predicted and closer to March 12 in Lake Alfred and March 18 in Sebring. Observations and the model agree that full bloom was later in Sebring than Lake Alfred. Usually, they have been reversed and less than 6 days apart. In most cases, overall flowering is better than last year. So far so good, but there still fruit set and growth to go. Usually, these factors are fairly steady and don’t contribute very much to yield variation.

It is hard to believe that there may still be a carryover effect from the 2004-05 hurricanes but the predicted 2007-08 yield per mature tree equivalents (MTE) supports that the effect was still in place this year. The lateness of the heaviest flowering wave was a clue, but went unheeded by yours truly. Based on the NASS-Fla. Citrus Statistics projections and assuming a 5 % loss of trees from the 2006 tree inventory, early-midseason cultivars are producing about 3.75 boxes per MTE and late cultivars 2.85 boxes per MTE this season. MTE is calculated based on tree age and average yields of that age compared to full size (mature) trees. For 40 years, the MTE yields have been 3.8 to 5.5 and 2.9 to 4.3, respectively, for early-mids and late cultivars. As you can see, this year’s yields are at the bottom of the ranges for each harvest range.

So what does next season hold in store for us! If you don’t mind my behaving like an economist and making some assumptions, here might be the scenario: We had a bloom equal to or slightly better than last year; Since bloom was still primarily in a later than expected wave of flowering, the trees are still not completely happy and will not set nor size fruit at their upper potential; We lose another 5 % of trees to disease and development; The remaining bearing trees come in just below or at an average yield per tree. This means that yield next season can be greater than this season, but any increase in Florida’s yield next season should be more than offset by an expected decrease of 10 to 20 % in Brazil’s production.

FLOWER BUD INDUCTION ADVISORY #1 for 2006-2007-11/01/06

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom
If you are not familiar with the website and flower bud induction in citrus you should read the overview section below the current status paragraph.

Overview of flower bud induction in Florida – Overview of flower bud induction in Florida – Citrus flower bud induction starts in the fall and usually is completed by early January. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F). A period of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be an El Niño year, lower than average temperatures and higher than average rainfall. Usually under these conditions, enough hours of low temperatures below 68 degrees F. accumulate to induce a good level of flower buds. Conditions that can interfere with good flower bud induction include: 1) several warm periods interrupt the induction process or 2) the previous crop was exceptionally high or 3) leaf loss from hurricanes was excessive and tree recovery was not complete. Two or three lead to low carbohydrate levels in developing buds which reduced their ability to become flower buds.

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 800 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction may occur after 700 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures > 80 to 85 degrees F., can trigger growth (bud swelling) if a minimum total hours of low temperatures have accumulated (400-500 hours below 68 degrees F). Later in the winter when the accumulated cool temperature induction hours are high, fewer days and lower daytime highs (75 degrees F.) are required in a warm period to stimulate growth of buds. Weather information relative to Florida citrus flower bud development for the current and several previous year’s (back to 1998) can be obtained from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. An 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt for the next week.

Some flower buds will be induced in the range of 300 to 450 accumulated hrs < 68 degrees F. Warm events just after these levels of induction result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well watered. The first situation results in multiple cohorts of flower buds developing to different bloom dates. The second condition leads to low flowering-fruit set and excessive spring vegetative growth. During the years from 1963 to 2003, multiple blooms occurred in over half of the years. Historically, the time period in which an early warm period (7-12 day) can lead to an initial low number of buds growing is roughly mid-November to mid-December. Then additional flower buds develop later resulting in multiple blooms. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is sufficient drought stress to stop growth. This water stress may be provided by stopping irrigation well before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a coincident short period of drought stress will have little impact on current crop development or quality. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition in citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts of cool periods. Sufficiently cool temperatures will prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper, sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. Soil moisture monitoring can help to achieve these goals. Prolonged late-fall, early-winter drought may be risky for ‘Hamlin’ or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus’. Figure 1 represents the different aspects of flower induction as depicted by the software program. The program gives an average bloom situation represented by the shades of green to white, vegetative to heavy flowering respectively. If the current crop is very heavy, then the greener shaded bands should be broader (require more hours for the same level of flowering). If the current crop is lighter or tree condition better, then the bands should be narrower as the level of potential flowering would be greater at lower total cool temperature hours. Although this representation does not appear on the working screen, recommendations (bottom text box) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process.

Weekly or bi-weekly advisories will follow this preliminary one and update the reader on accumulating hours of related cool or warm temperatures and other weather effects on flower bud induction. Methods for enhancing (urea or PO3 sprays) or reducing (GA3 sprays) flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

Previous responses -- In the winter of 2001-2002 following a good crop, cool temperature accumulation was very slow and low (640 hours accumulated), warm temperatures persisted and most buds started to grow by 20 December, particularly in well irrigated blocks, leading to excessive vegetative buds. This resulted in few buds remaining for a second flowering wave and a small crop occurred (2002-03 crop). By late December in the winter of 2002-2003, we had 850 hours of uninterrupted cool inductive temperatures with a low current crop on the trees. The following warm period initiated almost all the buds on all of the spring and summer flush to differentiate and bloom in early March. Still we had a fairly leafy bloom of very short duration (slightly more than 2 weeks). In spite of the high temperatures during and following bloom, an excellent fruit set occurred in all round oranges resulting in the highest October Florida citrus crop forecast by the Florida Agric. Statistical Service ever (2003-04 crop). In the winter of 2003-2004, there was good flower bud induction and reasonably good fruit setting conditions, although the heavy previous crop probably reduced flowering levels and set. Even though fruit size was small, it looked like we were headed for a 220 million box orange yield before the 2004 hurricanes significantly reduced the 2004-05 crop.

In the 2004-2005 winter citrus trees that were not in the path of the hurricanes had two years of good to heavy crops so a high level of induction was needed to produce adequate flower buds for the 2005-06 crop. If the block was in the path of one to three hurricanes, and the trees lost fruit but not many leaves, the trees needed slightly less inductive temperatures since bud carbohydrate levels improved some, but fruit losses were after most of the summer-early fall drain on carbohydrates had occurred. If many leaves were lost along with the crop, then trees were fairly low in carbohydrate and needed high levels of inductive temperatures to produce a good bloom.

If heavy fruit and leaf loss stimulated a strong early fall flush, then more buds were available from the previous year’s spring and summer flush for flowering , as after Hurricane Charlie, but the fall flush did not mature adequately if flush was produced after Hurricane Jeanne. Generally, enough fall-flush matured to provide flowering for a crop of about 200-210 million boxes of oranges and 30 million boxes of grapefruit for the 2005-06 crop, a significant recovery, before tree losses to canker and fruit losses to Hurricane Wilma reduced the crop again.

The 2005-06 winter had cool periods and sufficient cool weather occurred to slow down or stop vegetative growth on mature trees and then 800 to 1200 hrs < 68 degrees F. accumulated from southern to northern districts, respectively, for the first flowering wave in late February. An additional 200 hours occurred in many districts for a second cohort of buds to flower in early to mid-March. In some locations, flower bud development had sufficiently progressed for a February 13-14 frost to damage the more advanced buds. To view specific FAWN data for a location near you in the citrus growing areas for the induction weather or the frost temperature use (www.crec.ifas.ufl.edu ) and click on FAWN under weather or for NOAA’s 8 day forecast go to Weather Links on our CREC homepage and then 8 day forecast. Although last winter’s cold induction was good, poor tree condition after one or two years of hurricanes and the spring frost lead to a low crop, predicted at 135 million boxes of oranges.

Current status for 2006-07 winter - The light crop and general tree recovery without a hurricane should be promising for good flowering next spring. Although this is supposed to be an El Niño winter with cooler and wetter than normal weather, better than average cool temperature accumulation can occur only if warm periods do not interrupt the accumulation process. Currently, citrus locations have accumulated low temperatures < 68 degrees F of 150 to 300 hours from southern to northern areas, respectively. The next 8 days will be average for cool temperatures and another 80 to 100 hours should accumulate. Continued accumulation of cool temperatures and prevention of growth during a winter warm spell are important for a good start for the 2007-08 citrus production. Therefore, start to monitor irrigation amounts so drought stress can occur if a warm period occurs between November 15 and December 15 or Christmas, depending on the rate of cool temperature accumulation and reaching an acceptable level of 800 hours. Prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory.

(Request for potential cooperators) – Although rains in past winters often negated attempts to use drought stress to delay bloom in many areas, last winter was a good year to obtain this effect and growers that applied prolonged drought stress in late winter delayed bloom and avoided the damage to open buds caused by the February freeze. We are still interested in tests to delay bloom by managing irrigation to delay initiation of flower bud growth. This may be accomplished by withholding or restricting irrigation to prevent growth during warm winter periods until mid-January has passed. If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under this protocol.

FLOWER BUD INDUCTION ADVISORY #2 for 2006-2007-11/7/06

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review Advisory #1 for this year if you have not done so. Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data.

Current status for 2006-07 winter - The light crop and general tree recovery without a hurricane should be promising for good flowering next spring. Although this is supposed to be an El Niño winter with cooler and wetter than normal weather, better than average cool temperature accumulation can occur only if warm periods do not interrupt the accumulation process. Through November 6th, citrus locations had accumulated low temperatures < 68 degrees F of 160 to 300 hours from southern to most northern areas, respectively. The next 8 day forecast calls for cooler temperatures and another 100 to 140 hours < 68 degrees F should accumulate. The most northern FAWN site has now accumulated 400 hours and by next week this total should exceed 550 hours. (These numbers look suspiciously like a week ago, but that is what the program says).

Continued accumulation of cool temperatures and prevention of growth during a winter warm spell are important for a good start for the 2007-08 citrus production. After next week we could have bud growth initiated if a warm period occurred. Therefore, start to monitor and reduce irrigation amounts so drought stress can occur if a warm period occurs between November 15 and December 15 or Christmas, depending on the rate of cool temperature accumulation and reaching an acceptable level of 800 hours. Prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory. See last weeks background advisory for irrigation details.

(Request for potential cooperators) – Although rains in past winters often negated attempts to use drought stress to delay bloom in many areas, last winter was a good year to obtain this effect and growers that applied prolonged drought stress in late winter delayed bloom and avoided the damage to open buds caused by the February freeze. We are still interested in tests to delay bloom by managing irrigation to delay initiation of flower bud growth. This may be accomplished by withholding or restricting irrigation to prevent growth during warm winter periods until mid-January has passed. We may be able to help you monitor this effort. If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under this protocol.

Note: There may not be an advisory next week as I will be traveling. Look at FAWN, use the on-line monitor and the NOAA 8 day forecast.

FLOWER BUD INDUCTION ADVISORY #3 for 2006-2007-11/22/06

Please review the background information in the first advisory if you have not already done so.

Current Status: Cool temperature accumulation has now reached 320 to 600 hrs < 68 degrees F., from southern to northern citrus districts. Also, the National Weather Service (NOAA) predicts that there will be an additional 100 or more hours below < 68 degrees F. during the next 8 days. To view specific FAWN data for a location near you in the citrus growing areas, use (https://crec.ifas.ufl.edu/) and click on FAWN or for NOAA’s 8 day forecast go to Weather Links on our CREC homepage and then the NOAA 8 day forecast. See this season’s first advisory for how to run the flower monitoring system yourself.

This week’s cool weather should bring buds to a moderately low to moderate flower bud induction level where an extended warm period, 7 to 10 days with max. temperatures > 80 degrees F, would stimulate the easy to induce buds to begin differentiation. Continued accumulation of cool temperatures and prevention of growth initiation during a winter warm spell are important to a good start for flower formation for the 2007-08 harvest season. Therefore, keep irrigation amounts low or moderate (if fruit are still present) to minimize growth possibilities. Prepare to stop irrigation all-together and keep groves relatively dry, keep track of induction hours in your area, and watch NOAA’s 8-day forecast for possible warm weather that could force initiation of bud growth. Remember this protocol is advised at least until Christmas.

‘Plan ahead’ In a week or two, the advisory will discuss options if a warm spell prediction develops on the NOAA forecast for the period before Christmas.

(Request for potential cooperators) – Although rains this past winter negated attempts to use drought stress to delay bloom in many areas and collection of meaningful yields was severely disrupted by the hurricanes, we are still interested in tests to delay bloom by managing irrigation to delay initiation of flower bud growth. This might be accomplished by withholding or restricting irrigation to prevent growth during warm winter periods until mid-January has passed. If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under this protocol.

FLOWER BUD INDUCTION ADVISORY #4 for 2006-2007-11/30/06

Please review the background information in the first advisory if you have not already done so.

Current Status: Cool temperature accumulation has now reached 490 to 800 hrs < 68 degrees F., from southern to northern citrus districts. Also, the National Weather Service (NOAA) predicts that there will be an additional 100 or more hours below < 68 degrees F. during the next 8 days. To view specific FAWN data for a location near you in the citrus growing areas, use (https://crec.ifas.ufl.edu/) and click on FAWN or for NOAA’s 8 day forecast go to Weather Links on our CREC homepage and then the NOAA 8 day forecast. See this season’s first advisory for how to run the flower monitoring system yourself.

This week’s warm weather is of some concern as it might be warm enough for long enough to stimulate initiation of some bud growth since bud condition has now reached the moderately low to moderate flower bud induction level in most districts. An extended warm period, 7 to 10 days with max. temperatures > 80 degrees F, might stimulate the easy to induce buds to begin differentiation. This week is very close to the threshold. Follow the Flower Monitor Program closely for your area for the next 3 or 4 days to see if it shows the initiation of a flowering event. If you had stopped irrigation and soil was dry before the rains of the last 3 days, you might have helped to avoid as early initiation of growth. NOAA predicts that a cold front will reach us this weekend. Follow the NOAA’s 8-day forecast for possible extension of the warm weather (stalled or diverted front). Extension of this warm period would almost guarantee initiation of bud growth if soil moisture is adequate. It is particularly advised to not irrigate until this warm spell ends and then manage for some stress until Christmas to stop any early growth.

‘Plan ahead’ Next week, I will discuss options if another warm period prediction develops on the NOAA forecast for the period before Christmas and we have less than 800 hours of cool temperatures..

(Request for potential cooperators) – Although winter rains often negate attempts to use drought stress to delay bloom in many areas of Florida, we are still interested in tests to delay bloom by managing irrigation to prevent initiation of flower bud growth. This might be accomplished by withholding or restricting irrigation to prevent growth during warm winter periods until mid-January has passed. We have had a couple of volunteers that have agreed to cooperate and could use some more. If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under this protocol.

FLOWER BUD INDUCTION ADVISORY #5 for 2006-2007-12/8/06

Please review the background information in the first advisory if you have not already done so.

Current Status: Cool temperature accumulation has now reached 530 to 900 hrs < 68 degrees F., from southern to northern citrus districts. Also, the National Weather Service (NOAA) predicts that there will be an additional 75 to 110 hours below < 68 degrees F. during the next 8 days. The 8 day forecast does not indicate that any significant warming trend is anticipated to start in the next 8 days. However, trees are now ready to initiate bud growth if a week-long warm period did occur.

To view specific FAWN data for a location near you in the citrus growing areas, use (https://crec.ifas.ufl.edu/) go to Weather and click on FAWN or NOAA’s 8 day forecast. See this season’s first advisory for how to run the flower monitoring system yourself.

Last week’s warm weather was of some concern as it appeared warm enough and long enough to stimulate initiation of some bud growth since bud condition had reached the moderately low to moderate flower bud induction level in most districts. As of today, the Flowering Monitor Program does not indicate the initiation of a flowering event in any area except Umatilla, which has 900 accumulated cool hours. In 2 weeks we plan to check in other areas to see if there is any bud swell of the first two buds at the terminal end of last year’s summer shoots. If there is, then the program is over-estimating the amount of warm weather needed to stimulate bud growth. In the past the monitor program has been very accurate at predicting initiation of growth. This would be the first test as to whether it in some cases it may underestimate the number of flowering events in a season. You can check your trees in a couple of weeks to see if any bud swell is evident. If there is, please email that information so we can adjust the model.

If you had stopped irrigation and the soil was sufficiently dry to prevent growth during this past week, you should not have any bud swell in two weeks. You should continue to keep the soil relative dry and stop irrigating if a warm period is predicted by NOAA. It is particularly advised to manage irrigation for quick initiation of drought stress until Christmas to stop any early growth.

‘Plan ahead’ It is time to start thinking about flower induction enhancing sprays (urea or phosphorous acid (PO3)). They will be most useful if a warm period is predicted from near to shortly after Christmas and the total hours < 68 degrees F. has not reach 800 hours if you have a moderate crop and 900-1000 hours if you have a heavy crop. If you are anticipating spraying one of these products, be sure you have material on hand. For urea, you need 53 to 60 lbs of urea available per acre you plan to treat. For a PO3 product you need 3 pints to 2 quarts per acre depending on which product you use (60 % P (3pts) or if 26 % P (2 qts) product). If a warm period occurs immediately following next week, it may be advisable to spray trees with a good to heavy crop no later than 3 to 4 days into the warm period. Next week, we will update the advisability of spraying by area. Of course southern areas have the least inductive conditions.

I visited several Hamlin blocks yesterday in the Auburndale area to observe some light and heavy crops under the same management. The high variability in crop load this year from block to block is more usual than unusual. Leaf color and available vegetative flush for next year’s flowers was reasonable on all of the trees. The heavy cropped trees had significant amounts of inside fruit as well as exterior fruit, while light crop trees had only outside fruit, and frequently, they had outside areas with little or no fruit. The light crop trees had a lot of late bloom fruit from summer flowering, indicating just how light the normal crop is. We will receive yield data for these blocks from before the 2004 hurricanes to see if they were out of phase at the time of the hurricanes or the first year after. More on this when we get the data and try to explain some of the long-term hurricane effects we are observing.

(Request for potential cooperators) – We still are interested in having growers put a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under a soil water deficit protocol to try to consolidate and/or delay spring bloom.

FLOWER BUD INDUCTION ADVISORY #6 for 2006-2007-12/14/06

Please review the background information in the first advisory if you have not already done so.

Current Status: Cool temperature accumulation has continued at a favorable pace in spite of temperatures being higher than expected, particularly as this is supposed to be an El Niño winter.  According to the Flowering Monitor System the citrus districts have now accumulated  610 to 1050 hrs < 68 degrees F., from southern to northern areas.  Also, the National Weather Service (NOAA) predicts that there will be an additional 84 hours below < 68 degrees F. during the next 8 days.  The 8 day forecast does not indicate that any significant warming trend is anticipated in the next week. However, trees are now ready to initiate bud growth if a week-long warm period did occur and the buds may initiate growth if daily highs continue to be near 80 degrees F.  This is because nearly two weeks of such weather have already occurred.  To view specific FAWN data for a location near you in the citrus growing areas, use (https://crec.ifas.ufl.edu/ ) go to Weather and click on FAWN or NOAA’s 8 day forecast.  See this season’s first advisory for how to access the Flower Monitor System on the Internet.

This week, the Flowering Monitor Program still does not indicate the initiation of a flowering event in any area except Umatilla, which has 1050 accumulated cool hours.  Balm data appears to be in error (over 1000 cool hours) and therefore shows initiation of flower bud growth.  Next week we plan to check for bud swell of the first two buds at the terminal end of last year’s summer shoots.  You can check your trees before Christmas to see if any bud swell is evident.  If there is, please email that information so we can adjust the model.

If you had stopped irrigation and the soil was sufficiently dry to prevent growth during the past 2 weeks, you should not have any bud swell.  You should continue to keep the soil relative dry and stop irrigating if a warm period is predicted by NOAA.  It is particularly advised to manage irrigation by using small applications so that quick initiation of drought stress will occur if you stop irrigation.  This protocol should be considered to prevent growth until after Christmas .

‘Plan ahead’ It is time to start thinking about flower induction enhancing sprays (urea or phosphorous acid (PO3)).  These sprays will be most useful if a warm period is predicted from near to shortly after Christmas and the total hours < 68 degrees F. has not reach 800 hours if you have a moderate to low crop and 900-1000 hours if you have a heavy crop.  These conditions would most likely exist in the southern citrus growing areas.  If you are anticipating spraying one of these products, be sure you have material on hand.  For urea, you need 53 to 60 lbs of urea available per acre you plan to treat.  For a PO3 product you need 3 pints to 2 quarts per acre depending on which product you use (60 % P (3pts) or if 26 % P (2 qts) product).  If a warm period occurs immediately following next week, it may be advisable to spray trees with a good to heavy crop no later than 3 to 4 days into the warm period. 

(Request for potential cooperators) – If you are interested in delaying the main bloom date by putting a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under a soil water deficit protocol.

FLOWER BUD INDUCTION ADVISORY #7 for 2006-2007-12/20/06

Please review the background information in the first advisory if you have not already done so.

Current Status: According to the Flowering Monitor System the citrus trees (buds) have accumulated 620 to 1150 hrs < 68 degrees F., from southern to northern areas. Also, the National Weather Service (NOAA) predicts that there will be an additional 130 hours below < 68 degrees F. during the next 8 days. The 8 day forecast does not indicate that any significant warming trend is anticipated in the next week, but daytime highs will continue to be fairly warm for this time of year and an El Niňo year.. To view specific FAWN data for a location near you in the citrus growing areas, use (https://crec.ifas.ufl.edu/) go to Weather and click on FAWN or NOAA’s 8 day forecast. See this season’s first advisory for how to access the Flowering Monitor System on the Internet.

This week, the Flowering Monitor Program still does not indicate the initiation of a flowering event in southern areas, but Lake Alfred and Umatilla do indicate bud growth with an early to mid-February bloom date estimate. But trees in many areas have initiated bud growth after the warm weather from late November through mid-December. I have one report of bud swell on trees in 2 or 3 areas south of Lake Alfred. I believe it may be a general condition in most areas. Have you checked some of your trees to see if any bud swell is evident?

Those two or three weeks of warm weather (highs just below or above 80 degrees F.) apparently were sufficient to initiate growth if soil moisture was available. At the time this bud growth started trees had accumulated from the mid-500s to 650 hours of cool temperatures. This is on the low side for best flowering. If you had stopped irrigation and the soil was sufficiently dry during most of the period from the November 16th rain until the December 14th rain occurred, you may not have any bud swell. Particularly if you are in the southern areas, you should continue to keep the soil relative dry and stop irrigating if another warm period is predicted by NOAA during the next two weeks. Manage irrigation by using small applications so that quick initiation of drought stress will occur if you stop irrigation. Let me know if you don’t see any bud swell in non-irrigated blocks.

‘Plan ahead’ There is still time to use flower induction enhancing sprays (urea or phosphorous acid (PO3)). Although in many or most cases the first wave of flower buds has started to grow, there will be further induction of other buds. At the time of the next warm period, the level of flowering in those buds can be increased by one of these sprays. The decision to spray should be based on how much additional cool weather occurs from December 14th until the warm period and if the total hours < 68 degrees F. has not reach 850 to 900 hours. If total hours exceed 1000 hours or the additional hours from December 15th exceed 500 hours at the beginning of the next warm period, I would not spray. For urea, you need to apply 53 to 60 lbs of urea per acre. For a PO3 product you should apply 3 pints to 2 quarts per acre depending on which product you use (60 % P (3pts) or if 26 % P (2 qts) product).

FLOWER BUD INDUCTION ADVISORY #8 for 2006-2007-1/3/07

Currently, all citrus areas have flower buds swollen and in many cases young leaflets are pushing. The Flowering Monitor System indicates this growth started about 10-12 December and the projected bloom dates for this first wave of flowers is about February 7 to 9 if normal or warmer weather continues. This first wave was induced at about 600 to 800 accumulated hours below 68 degrees F from southern to northern districts. The most northern district may flower even earlier, late January. If you are in this area you should examine flower buds to see if the first two buds on summer shoots are expanded to the exposed leaflet stage. If they are not, then the bloom date may be a little later than projected by the Flowering Monitor System. After the initiation of the first wave another 200 to 250 hours of cool temperatures have accumulated. It is likely that another wave of flower buds will initiate growth at the end of this week as daytime highs are projected to continue at above 75 degrees F. The bloom date for this wave would probably be in early March. The total accumulated hours will be from 700 to 1100 hours depending on the citrus growing district. The lowest levels of induction will be in the southern districts, particularly the Indian River. In those districts with low total induction, trees with a heavy crop or weak re-growth after the hurricanes may benefit from a spray of urea or PO3. Review the last advisory for more information about these sprays. If you choose to treat some acreage, these sprays should be applied at temperature near or above 70 degrees F. and within the next 5 to 7 days. There are some anticipated side effects of this year’s weather and projected two waves of flowering that will be about 1 month apart and cause a prolonged bloom period. This will make psyllid control more difficult. Also with an El Nino year and higher probability for spring rains, some post bloom fruit drop may emerge by the second flowering period.

FLOWER BUD INDUCTION ADVISORY #9 for 2006-2007-1/11/07

Currently, two waves of flower buds have initiated growth and some flower buds in the first wave are swollen and young leaflets are pushing from a few, most advanced vegetative buds (Fig 1 to 3). The Flowering Monitor System indicates this growth started about 10-12 December and the projected bloom dates for this first wave of flowers is now February 4 to 5, if normal or warmer weather continues as it has this past week. This first wave was induced at about 600 to 800 accumulated hours below 68 degrees F from southern to northern districts. The most northern district (Umatilla) may flower even earlier, 21 January.

After the initiation of the first wave another 200 to 250 hours of cool temperatures accumulated before the second wave initiated growth. This wave of flower buds is projected to bloom in early March (March 2 to 5). The total accumulated hours will be from 800 to 1050 hours depending on the citrus growing district. The lowest levels of induction are in the southern districts, particularly the Indian River (only 600 hours for the first wave and 720 for likely second wave).

Flower induction is essentially over. Now we can wait and see if the bloom dates will really be as early as projected. I only saw a scattered amount of buds with leaflets exposed, but the other buds will jump forward in development if we get another week of 80 degree weather.

Even if the 2 projected waves of flowering come later than early February and March, they will still be about 1 month apart and cause a prolonged bloom period. This will make psyllid control more difficult. Also with an El Nino year and higher probability for spring rains, some post bloom fruit drop may emerge by the second flowering period.

The crop potential for trees with a good current crop from the first wave of inducted buds will be weak, but the second wave had a moderate level of induction and maybe a medium crop can be anticipated overall for these trees. For light cropped trees, a reasonably heavy crop should occur if we have finally gotten over the residual hurricane effects. The real question is how many of each kind of tree do we now have?

 

FLOWER BUD INDUCTION ADVISORY #10 for 2006-2007-1/17/07

Currently, two waves of flower buds have initiated growth and some flower buds in the first wave are swollen, pushing out young leaflets on the most advanced vegetative buds and some pinhead flowers are now visible in most orange cultivars. The Flowering Monitor System indicates this growth started about 10-12 December and the projected bloom dates for this first wave of flowers are now February 2 to 6. This first wave was induced at about 600 to 800 accumulated hours below 68 degrees F from southern to northern districts. According to the model, the most northern district (Umatilla) may flower even earlier, 21 January. The only good thing I can say about this early flush is that it is a small percentage of the available buds and hopefully, the second wave will have most of the flowering, at a reasonable date.
This second wave of flower buds is projected to bloom in early March (March 2 to 5). The total accumulated hours will be from 800 to 1050 hours depending on the citrus growing district. The lowest levels of induction are in the southern districts, particularly the Indian River (only 600 hours for the first wave and 750 for a likely second wave).
Flower induction is essentially over. Now we can wait and see if the bloom dates will really be as early as projected. Last week I doubted the model, but the few buds that are pushing are expanding rapidly. I saw 2 or 3 inflorescences that were already an inch long with pinhead flowers.
Even if the 2 projected waves of flowering come later than early February and March, they will still be about 1 month apart and cause a prolonged bloom period. This will make psyllid control more difficult. Also with an El Nino year and higher probability for spring rains, some post bloom fruit drop may emerge by the second flowering period. 

The crop potential from the first wave of inducted buds appears to be low, but the second wave has a moderate level of induction and maybe a medium crop can be anticipated overall for these trees. For light cropped trees, a reasonably heavy crop should occur if we have finally gotten over the residual hurricane effects. The real question is how many of each kind of tree do we now have?
Florida temperatures are projected to be cooler the next few days, but citrus bud development should still progress so that the level of flowering in the first wave can be more accurately evaluated by next week.
Have you started your fertilizer program yet? The atmospheric jet stream pattern is still mostly from West to East so there is little chance of a freeze, particularly as we will be past the 20th this weekend with no evidence of a severe cold front coming down on us from the North. The main bloom should be about the first week of March. Fertilizer should be in the tree 1-2 weeks before that date.

FLOWER BUD INDUCTION ADVISORY #11 for 2006-2007-1/26/07

Flower bud induction is now stable and no changes in induction levels will occur. Currently, two waves of flower buds have initiated growth and some flower buds in the first wave are swollen, pushing out young leaflets on the most advanced vegetative buds and some pinhead flowers are now visible in most orange cultivars. The Flowering Monitor System indicates this growth started about 10-12 December. The first wave was induced at about 600 to 800 accumulated hours below 68 degrees F from southern to northern districts. The projected bloom dates have moved up so that the first wave of flowers may occur next week, just before 1 February or even earlier. The early flush still appears to be a small percentage of the available buds and hopefully, the second wave, end of February, will have most of the flowering.
The bloom date for this second wave of flower buds has moved up from the 1st week of March (March 2 to 5). The total accumulated hours will be from 800 to 1050 hours depending on the citrus growing district. The lowest levels of induction are in the southern districts, particularly the Indian River (only 600 hours for the first wave and 750 for a likely second wave). This week, flowers were evident on weak trees in the River District. We traveled to some citrus near Alligator Alley, below Clewiston, and saw many open flowers on the weaker trees. The healthier trees had pinhead to popcorn and some open flowers. Again these trees did not have a large percentage of their buds at this stage but other buds were swollen.
Even if the 2 projected waves of flowering come later than early February and March, they will still be about 1 month apart and cause a prolonged bloom period. This will make psyllid control more difficult. Also with an El Nino year and higher probability for spring rains, some post bloom fruit drop may emerge by the second flowering period. The flowering model does project that a third wave of flowering could happen by mid-March, further extending the flush-bloom period.
The crop potential from the first wave of inducted buds appears to be low, but the second wave has a moderate level of induction and maybe a medium crop can be anticipated overall for these trees. For light cropped trees, a reasonably heavy crop should occur if we have finally gotten over the residual hurricane effects on tree canopy condition. The real question is how many of each kind of tree do we now have?
Florida temperatures are projected to be cooler next week, but freezing temperatures are not predicted as far north as Leesburg, so hopefully none of the first wave of flowers will be lost. The atmospheric jet stream pattern is still mostly from West to East so there is little chance of a freeze.
Have you started your fertilizer program yet? The main bloom should be about the last week of February to the first week of March. Fertilizer should be in the tree at least 1-2 weeks before that date. Next weeks cold weather should not delay bloom very much. Continued cold weather after next week could delay bloom, but probably not more than 1 to 1 ½ weeks.

FLOWER BUD INDUCTION ADVISORY #12 for 2006-2007-2/6/07

Flower bud induction is now stable and no further changes in induction levels should occur. The first wave of flower buds initiated growth in early December, but was a small number of the total available buds. This wave of buds has flowered or is doing so now. Overall, the induction level when these flower buds started their growth was low. In the Central Florida area, the current cool weather has delayed this bloom a few days. Some trees in all districts have more flowers in this wave than is the general case for healthy trees. The stage of flowering is more advanced on these trees than on most trees with smaller amounts of open flowers also.
The bloom date for the second wave of flower buds is still projected to be around the 1st week of March. The total accumulated hours is from 800 to 1050 hours depending on the citrus growing district. Continued cool weather may delay the full bloom date, but probably not more than a week to 10 days at most. Although more buds are starting to show swelling and bud break, there are still many buds on apparently suitable flowering shoots not showing any growth, although some are swelling.
This suggests that the projected third wave of flower opening may occur as projected in mid-March. All areas would have over 1100 hours below 68 degrees F. for that flowering wave.
The crop potential from the first wave of inducted buds appears to be very low although more flowers were evident on trees in the more southern areas, the second wave now appears to be a moderate level of induction, but not enough buds are developing yet. Hopefully, more flowers will develop in a third wave of flowering. The projection of temperatures in the mid-70s later this week should cause more advancement and within the next two weeks we should be able to see most of the growing buds for this spring’s flush. Then we can better assess our crop potential for the 2007-08 harvest season.

FLOWER BUD INDUCTION ADVISORY #13 for 2006-2007-2/14/07

Flower bud induction is now stable and no further changes in induction levels should occur. The first wave of flower buds initiated growth in early December, but was a small number of the total available buds. This wave of buds has flowered. Overall, the induction level when these flower buds started their growth was low. In the Central Florida area, the current cool weather delayed this bloom a few days. Some trees in all districts have more flowers in this wave than is the general case for healthy trees. This wave will result in little fruit set on most trees.
The bloom date for the second wave of flower buds is still projected to be the end of February to the 1st week of March. A total of 800 to 1050 hours accumulated for this flowering wave depending on the citrus growing district. Continued cool weather may delay the full bloom date, but probably not more than a few days at most. Although more buds are starting to show swelling and bud break, there are still many buds on apparently suitable flowering shoots not showing any growth, although some are swelling. Based on the trees observed in Lake Alfred, it appears that there will be buds available for the projected third wave of flower opening as projected for mid-March. All areas have over 1100 hours below 68 degrees F. for that flowering wave.
In estimating the full bloom date remember that although a full bloom is projected for the majority of flowers at that stage, there is bud to bud variability and some flowers may open a week earlier or later than the average date. Also look at several trees within and between blocks. We have two Valencia blocks with very different proportions of flowering buds showing for the early March bloom. One block has many more buds pushing than the other, but neither has all of the available spring or summer shoots showing bud growth.
The main concern for this week is the projected cold weather on Saturday morning. If the projected low materializes on the Ridge and cold air drains to the low areas towards Arcadia and Immokalee, a large amount of the flush and flowers could be damaged. The National Weather Service is projecting 30 and 33 degrees F for the lows Saturday morning in Lakeland and Winter Haven, respectively. Everyone needs to keep a very close eye on the weather and evaluate multiple sources for low temperature projections.

FLOWER BUD INDUCTION ADVISORY #14 for 2006-2007-2/28/07

It looks like we will finally have the major bloom for 2007 in mid-March. The projected full bloom date for this wave is from March 17 to 21 depending on the citrus area. Will these buds reach full bloom in 3 weeks? The one anomaly in the ‘Flowering Monitor System’ is that Umatilla reportedly is past full bloom for all waves. I would appreciate some reports from the area north of Tavares as to whether this third wave is more nearly at the same stage, early feather growth, as is evident in central areas. Although more trees in the southern areas had substantial flowers in the earlier waves, trees examined this week from Lake Placid to Lake Alfred now have many buds breaking and new growth is mostly at the earliest feather stage with evidence of at least one flower mixed with the leaves in many of the buds. Tree to tree and canopy to canopy location variability is large with some canopy areas having considerable second wave flowers near full bloom, while other trees and canopy locations have few of these flowers, but many buds pushing or at least visibly swollen.
I thought that the second wave would be the major bloom, but it is going to be the third wave. This is good because on most trees, at least on the Ridge, we do not have enough flowers to provide an economic crop in the first two waves. Obviously, we still have work to do in order to understand all of the factors interacting with induction temperatures to determine how many buds can break and grow as flower buds for a given temperature induction level. A major factor determining flowering level is carbohydrates in the buds, but I had assumed that most trees, at least on the Ridge, are finally at adequate carbohydrate levels for a normal bloom after the 2004 hurricanes. There probably are some additional factors still to be understood.
Information from previous advisories
Flower bud induction is now stable and no further changes in induction levels should occur. The first wave of flower buds initiated growth in early December, but was a small number of the total available buds. This wave of buds has flowered. Overall, the induction level when these flower buds started their growth was low. In the Central Florida area, the cool weather delayed this bloom a few days. Some weaker trees in all districts had more flowers in this wave than is the general case for healthy trees. This wave will result in little fruit set on most trees.The bloom date for the second wave of flower buds was projected to be the end of February to the 1st week of March. This is holding true. A total of 800 to 1050 hours accumulated for this flowering wave depending on the citrus growing district. Although more buds were growing in this second wave, there were still many buds on apparently suitable flowering shoots not showing any growth, although some were swelling. Based on the trees observed in Lake Alfred, it appears that there will be buds available for the projected third wave of flower opening as projected for a mid-March bloom. All areas have over 1100 hours below 68 degrees F. for that flowering wave.
In estimating the full bloom date remember that although a full bloom is projected for the majority of flowers at that stage, there is bud to bud variability and some flowers may open a week earlier or later than the average date. Also look at several trees within and between blocks. We have two Valencia blocks with very different proportions of flowering buds showing for the early March bloom. One block had many more buds pushing than the other, but neither had all of the available spring or summer shoots showing bud growth.

FLOWER BUD INDUCTION ADVISORY #15 for 2006-2007-3/7/07

It definitely looks like we will finally have the major bloom for 2007 in mid-March. The projected full bloom date for this wave is from March 16 to 20 depending on the citrus area. Will these buds reach full bloom in 2 weeks? In the Lake Placid area, many of these inflorescence shoots are an inch long and large pinhead, but still green blossoms are visible. On the central Ridge, the growth is shorter, but many buds have feather leaves and small pinhead flowers. These should expand rapidly. Many shoots are showing this condition, with the most vigorous summer shots having fewer buds growing. Although in some canopy zones, a lot of this growth is vegetative only, the majority of the new growth has one or more flowers now visible.
In central Florida, the second wave is just at full bloom or at the popcorn stage. This is about a one week delay from the originally predicted bloom date. On trees in the southern Ridge area, these blossoms are slightly more advanced. Some trees have a fair amount of this stage, but in the locations I have seen it does not equal the flowering coming in the third wave for mid-March. Fruit from the first wave are about ¼ inch diameter.
By the middle of next week, we should be able to assess the blossom numbers in the inflorescences and establish the typical flower to leaf ratio. New leaf production in mixed inflorescences is important to setting fruit through the May-June drop period. How many buds on each shoot are flowering is a good indicator of what the overall crop potential will be. We can revisit these issues next week.

FLOWER BUD INDUCTION ADVISORY #16 for 2006-2007-3/19/07

he major bloom for most trees in 2007 will be at least next week or a little later (25 to 30 March). The projected full bloom date for this wave was from March 16 to 20 depending on the citrus area, but just as the second wave of flowers was about a week to 10 days late due to cooler weather, this larger wave will follow the same delay. In central Florida, this last wave looks strong with flowers ranging in development from pinhead to a few in the popcorn stage.
In an average year, 80 % of the flowers occur in the first 4 terminal end bud positions (4 leaf axis). It appears that many shoots have 5 to 7inflorescenses (buds) that will produce flowers, but of course some have none. This may be a bit above average and most of the buds have produced mixed inflorescences with a fair number of leaves. This speaks well for the next crop to be back to normal.
Data from one Central Florida grower indicates that 4 Hamlin blocks had still not recovered to normal production with this 2006-07 harvest. This was apparently due to lingering effects of the three 2004 hurricanes. All of these blocks are producing a heavy flowering wave now that appears to be at normal levels and similar to most trees in this area.
At what level will next years crop be? If we have good numbers of remaining mature trees after the hurricanes, canker, development and greening losses of grove, then we should be able to project our likely level of recovery.

FLOWER BUD INDUCTION ADVISORY #17 for 2006-2007-4/5/07

In the last advisory I stated that ‘The major bloom for most trees in 2007 will be at least next week or a little later (25 to 30 March)’. In fact for most trees, full bloom has just pasted early this week. That is about a 2 week delay from the model, partially due to cooler weather, but the result is clearly the major bloom for the year. Bloom the first week of April has occurred before and the crop that develops will likely be later in maturing. Further, there is good flowering inside most canopies as well as in the outer canopy. If fruit set is normal, we should have a good to very good yield per tree. Will fruit set be normal?
We are at the beginning of the hot, dry spring period that occurs every year. In the past 30 years, there have been only a handful of cases where climatic conditions were extreme enough to change the normal pattern of fruit set. Of course if you don’t irrigate during this period until the June rains start, fruit set will be significantly reduced (R.C.J. Koo, 1960s).
In 2 months we can revisit the situation and see if any unusual weather pattern occurred. For now, provide good irrigation scheduling and if your trees are healthy, you should have a good crop this year.

FLOWER BUD INDUCTION ADVISORY #18 for 2006-2007-6/13/07

The major bloom for most trees in 2007 was in late March to early April. Bloom the first week of April has occurred before and the crop that develops will likely be later in maturing. Further, there was good flowering inside most canopies as well as in the outer canopy.
At bloom time, the major issue became ‘Will fruit set be normal?’ The answer is yes. We should have a very good yield per tree, especially compared to the two previous years.
Examination of trees in the Auburndale-Lake Alfred area indicated that set is good, very little drop will occur from this point until neat harvest. Just an occasional yellowing fruit was observed and mostly on Valencia trees. Unfortunately, I have not observed set in more southern regions and the coast, but bloom was similar in all areas, late and heavy. Fruit set in some southern areas may be adversely affected if irrigation was restricted due to water shortages.
Fruit size is golf ball for Hamlin and a little smaller for Valencia. Grapefruit were of course bigger as were navel fruit. The only trees that showed much set from earlier flowering waves were navels. Fruit size may be a little behind some years, but the late bloom did allow early development in warmer than normal temperatures and the result was a fast start on fruit growth.
The major issues for what our 2007-08 harvest will be are hurricanes, freezes and how many mature trees we have left. Temperatures (warm ocean waters) will favor major hurricanes, but it is anyone’s guess as to their path. The winter temperatures and rainfall will follow a Neutral or La Nina pattern, which increases the chance of a freeze. Barring one or more of these catastrophes, we should have a very good crop, but the tree census is still being worked on. We haven’t had a good crop on our reduced tree numbers to see what the new medium and high production levels can be. Some people have said that they expect a new high would be in the low 200 million box level. The fruit set appears to be a little short of whatever the new potential is.

FLOWER BUD INDUCTION ADVISORY #1 for 2005-2006-11/28/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Overview of flower bud induction in Florida – Citrus flower bud induction is progressing for the coming year's bloom. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F). A period of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be a neutral El Ni ñ o year, average temperature and rainfall. Usually under these average conditions, enough hours of low temperatures below 68 degrees F. should accumulate to induce a moderate to good level of flower buds. Conditions that can interfere with good flower bud induction include: 1) several warm periods interrupt the induction process or 2) the previous crop was exceptionally high or 3) leaf loss from hurricanes was excessive the previous year. Two or three lead to low carbohydrate levels for developing buds.

Under normal Florida weather conditions but with a moderate to heavy previous crop, sufficient flower bud induction should be achieved when total accumulated hours of low temperatures exceed 850 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction can occur after 700 to 750 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures > 75 to 80 degrees F., can trigger growth (bud swelling) after a minimum of low temperatures have accumulated (500 hours below 68 degrees F). Fewer days and lower daytime highs in a warm period are required to stimulate growth of buds later in the winter when the accumulated cool temperature induction hours are high. Current and previous year's weather information relative to Florida citrus flower bud development can be obtained from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. The 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt and is linked to http://www.crec.ifas.ufl.edu/crechome/crecweather.shtml.

Some flower buds will be induced in the range of 300 to 600 accumulated hrs < 68 degrees F. Warm events after these levels of induction result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods, or these buds may sprout as vegetative shoots if warm weather continues and the trees are well watered. This situation results in multiple cohorts of flower buds developing to different bloom dates. During the years from 1963 to 2004, multiple blooms occurred in over half of the years. Historically, the time period in which a early warm 7-12 day period can lead to some buds growing and then additional bud develop result in multiple blooms is roughly mid-November to mid-December. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is to promote water stress by stopping irrigation before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a short period of drought stress will have little impact on current crop development or quality. Sufficient drought stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a drought stress condition of citrus trees, buds will not grow in response to high temperatures. If a warm period has passed, trees again can be irrigated to minimize current crop stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts of cool periods. The cool temperatures will prevent growth even though soil moisture is adequate for growth. Since winter rains usually occur just before cool temperatures, the chances that drought stress will prevent an early flower bud differentiation event are reasonably good for many warm periods. Even so, growers in some growing districts have often found it difficult to maintain winter drought stress in recent years.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 to 8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. This may be risky for ‘Hamlin' or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus'. Figure 1 represents the different aspects of flower induction as depicted by the software program. Some added information in color or bold lettering is intended to assist with interpretation. The level of potential flowering would be greater (orange line) with a light crop or less (green line) with a heavy crop for the same amount of hours of induction. Although this representation does not appear on the working screen, recommendations (bottom text box) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process. We are working to make the system available on-line shortly. In the meantime, the weekly advisories will update accumulating hours of related temperatures and other weather effects on flower bud induction. Methods for enhancing or reducing flowering intensity as conditions and cultivars dictate will be discussed in later advisories. Read the archived advisories from previous years (link at top of this page) for more background.

Previous 4-year's results – In the winter of 2001-2002 cool temperature accumulation was very slow, warm temperatures persisted and most buds started to grow by 20 December, particularly in well irrigated blocks, leading to excessive vegetative buds. This resulted in few buds remaining for a second flowering wave and a small crop occurred. By late December in the winter of 2003-2003 we had 850 hours of uninterrupted cool inductive temperatures with a low current crop on the trees. The following warm period initiated almost all the buds on all of the spring and summer flush to differentiate and bloom in early March. We had a fairly leafy bloom of very short duration (slightly more than 2 weeks). In spite of the high temperatures during and following bloom, an excellent fruit set occurred in all round oranges resulting in the highest FASS October crop forecast for Florida ever. In 2003-2004, there was good flower bud induction and reasonably good fruit setting conditions, although the heavy previous crop probably reduced flowering levels and set. Even though fruit size was small, it looked like we were headed for a 220 million box orange yield before the hurricanes.

Last year citrus trees that were not in the path of the hurricanes had two years of good to heavy crops so a high level of induction was needed to produce adequate flower buds for the current year's crop. If the block was in the path of one to three hurricanes, and the trees lost fruit but not many leaves, the trees needed slightly less inductive temperatures since bud carbohydrate levels could improve some, but fruit losses were after most of the summer-early fall drain on carbohydrates had occurred. If many leaves were lost along with the crop, then trees were fairly low in carbohydrate and needed high levels of inductive temperatures to produce a good bloom.

If heavy fruit and leaf loss stimulated a strong fall flush, then more buds were available on last year's spring and summer flush for flowering if the fall flush came after Hurricane Charlie, but the fall flush did not mature adequately if flush was produced after Hurricane Jeanne. Generally, enough fall flush matured to provide flowering for a crop of about 210 million boxes of oranges and 30 million boxes of grapefruit, a significant recovery, before tree losses to canker and fruit losses to Hurricane Wilma reduced the crop potential again.

The new season's situation – Two cool periods have occurred this Fall. Sufficient cool weather has occurred to slow down or stop vegetative growth on mature trees, 320 to 630 hrs < 68 degrees F., from southern to northern districts. An additional 80 to 108 hours are predicted for the next 8 days. No steady warm period is predicted for these next 8 days. To view specific FAWN data for a location near you in the citrus growing areas, use https://crec.ifas.ufl.edu/ and click on FAWN or for NOAA's 8 day forecast go to Weather Links on our CREC homepage and then 8 day forecast.

The major concern for the next 20 days is the possibility of an extended warm period, 10 to 12 days with max. temperatures > 75 to 80 degrees F, in early to mid-December which would initiate differentiation of easily induced flower buds. Continued accumulation of cool temperatures or prevention of growth during a winter warm spell is important for a good start for the 2006-07 citrus crop. Therefore, keep irrigation amounts low to moderate (if fruit are still present) to minimize growth possibilities. Prepare to make groves relatively dry by withholding irrigation if a warm period is predicted. Keep track of induction hours in your area and watch for the next advisory.

(Request for potential cooperators) – Although rains this past winter negated attempts to use drought stress to delay bloom in many areas and collection of meaningful yields was severely disrupted by the hurricanes, we are still interested in tests to delay bloom by managing irrigation to delay initiation of flower bud growth. This might be accomplished by withholding or restricting irrigation to prevent growth during warm winter periods until mid-January has passed. If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin' or ‘ Valencia ' trees under this protocol.

FLOWER BUD INDUCTION ADVISORY #2 for 2005-2006-12/05/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review the background information in the first advisory if you have not already done so.

Current Status: Cool temperature accumulation has now reached 420 to 760 hrs < 68 degrees F., from southern to northern citrus districts. Also, the National Weather Service (NOAA) predicts that there will be about 96 to 110 additional hours below < 68 degrees F. during the next 8 days. To view specific FAWN data for a location near you in the citrus growing areas, use https://crec.ifas.ufl.edu/ and click on FAWN or for NOAA's 8 day forecast go to Weather Links on our CREC homepage and then the NOAA 8 day forecast.

This week's cool weather should bring buds to a moderately low to moderate flower bud induction level where an extended warm period, 7 to 10 days with max. temperatures > 80 degrees F, would stimulate the easy to induce buds to begin differentiation. Continued accumulation of cool temperatures and prevention of growth initiation during a winter warm spell are important to a good start to the 2006-07 harvest season. Therefore, keep irrigation amounts low or moderate (if fruit are still present) to minimize growth possibilities. Prepare to stop irrigation all-together and keep groves relatively dry, keep track of induction hours in your area, and watch NOAA's 8-day forecast for possible warm weather that could force initiation of bud growth. Remember this protocol is advised at least until Christmas.

By next week, it will be appropriate to consider a urea or phosphorous acid spray if a warm spell comes by Christmas and it is not possible to stop bud development by maintaining drought stress. Next week, I will review the protocol for those sprays and their timing at the beginning of a warm spell. Remember that materials and properly working sprayers are needed for these sprayers. Aerial application needs to be arranged in advance. ‘Plan ahead' A midweek advisory will be posted if a warm spell prediction develops on the NOAA forecast.

(Request for potential cooperators) – Although rains this past winter negated attempts to use drought stress to delay bloom in many areas and collection of meaningful yields was severely disrupted by the hurricanes, we are still interested in tests to delay bloom by managing irrigation to delay initiation of flower bud growth. This might be accomplished by withholding or restricting irrigation to prevent growth during warm winter periods until mid-January has passed. If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin' or ‘ Valencia ' trees under this protocol.

FLOWER BUD INDUCTION ADVISORY #3 for 2005-2006-12/13/05

Please review the background information in the first advisory if you have not already done so.

Current Status: Accumulated cool weather has now reached 490 to nearly 900 hr < 68 degrees F. from southern to northern citrus districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be 168 additional hours below 68 degrees F. during the next 7 days (max temperatures below 68 degrees F. for 1 week). This means that all areas will be at least in the moderate range of flowering potential by next week. The cooler districts should reach the first stage of the high range, exceeding 900 hours. To view specific FAWN data for a location near you in the citrus growing areas, use https://crec.ifas.ufl.edu/ and click on FAWN, or for NOAA's 8 day forecast go to Weather Links on our CREC homepage and then 8 day forecast.

Up to now, cool temperature accumulation has been at a good, almost constant rate. Two more weeks of cool weather will place all districts in a good position. This requires the NOAA 8-day forecast to continue in the plus 100 hrs per week range until Christmas. Rainfall has prevented soil moisture from depleting to provide drought conditions which could inhibit flower buds growth. So a warm period in December will now stimulate the terminal buds on spring and summer shoots to initiate growth. A sufficient warm period is probably 5 to 7 days in the low-80s.

If we are in the 800 accumulated hours < 68 degrees F. range when a warm period starts, you may want to consider using a flower bud induction enhancing spray of either urea or phosphorous acid (PO3. If you are anticipating spraying one of these products, be sure you have material on hand. For urea, you need 53 to 60 lbs of urea available per acre you plan to treat. For a PO3 product you need 3 pints to 2 quarts per acre depending on which product you use (60 % P (3pts) or if 26 % P (2 qts) product). Trees with severe defoliation from hurricanes this summer followed by a strong fall flush may be good candidates for these sprays this winter since their buds may be harder to induce to be flower buds. Sprays can be applied at low volume, even aerial if with a good distribution system. Application time should be just as the warm period is starting, when daytime highs are in the 70 degree range, and may continue for up to a week. Sprayed trees will often bloom up to a week earlier than unsprayed controls.

If cool weather continues into early January, it will not be necessary to enhance flower bud induction. At that time, a GA spray may be advisable to reduce flowering in cultivars like mandarins. If cool weather is predicted to continue, I will discuss GA use next week.

FLOWER BUD INDUCTION ADVISORY #4 for 2005-2006-12/19/05

Please review the background information in the first advisory if you have not already done so.

Current Status: Accumulated cool weather has now reached 600 to nearly 1050 hr < 68 degrees F. from southern to northern citrus districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be 110 to 140 additional hours below 68 degrees F. during the next 7 days. This means that all areas will be at least in the moderate-high range of flowering potential by next week. The cooler districts are in the high range, exceeding 900 hours. Some northern areas will reach the very high range by the end of this coming 8-day period. To view specific FAWN data for a location near you, use https://crec.ifas.ufl.edu/ and click on FAWN, or for NOAA's 8-day forecast go to Weather Links on our CREC homepage and then 8-day forecast.

Up to now, cool temperature accumulation has been at a good, almost constant rate and is predicted to continue this week according to the NOAA 8-day forecast. One more week of cool weather after this week (until January 1 st ) will place all districts in an excellent position for heavy flowering if trees are healthy and had a moderate crop up to or after Hurricane Wilma. Rainfall has prevented soil moisture from depleting to provide drought conditions which could inhibit flower buds growth, but no extended warm period has occurred to cause an early bud growth problem.

See earlier advisories about planning for and using urea or PO3 sprays to enhance flowering. The need for using one of these sprays is greatly diminished. Growers may still want to consider using these sprays on weak (poor root system) or heavily bearing blocks, particularly in southern areas. If used, these sprays should be applied as the weather warms up at the first warm period, and you can have effective results until 3 or 4 days into the warm period. Usually, this provides a 7 day spray window for these applications. If cool temperatures last through the first week of January, it is much less likely that these sprays will be beneficial since a very good level of natural flower bud induction will have been reached.

With the high levels of induction hours that will have accumulated by Christmas, it is now time to worry about excessive flowering. Too many flowers in seedless cultivars (navels), hybrid blocks with a moderate to light crop and some strains of Rhode Red Valencia that set poorly result either in too much flower competition and poor set (navels and some Rhode Reds) or in excessive set (mandarin hybrids) and poor fruit size. A GA 3 spray is advised towards the end of the first warm spell that has 4 to 5 days exceeding 73 to 75 degrees F, note that these temperatures are now lower than stated previously because the intensity level of induction is now higher. The above cultivars are likely to have excessive flowering with few leaves associated with the inflorescence. GA 3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. Need for and best timing for a GA 3 spray in the various production zones will be assessed in coming advisories.

A new concern regarding winter management is the possibility of a freeze. Levels of cold hardiness are good now and should stay that way until a warm period occurs. This is an El Niño Neutral year, which increases the likelihood of a freeze. Generally, a hard freeze is most likely until we get pasted January 15 th to 20 th . If a warm period occurs before that date, some or all of cold hardiness will be lost if the buds start to swell and grow. Being able to apply drought stress is one way to prevent loss of cold hardiness. If winter rains stop and you keep soil moisture on the low side, you may benefit by shutting down irrigation if a warm period is predicted by a NOAA 8-day forecast.

The Web based Citrus Flowering Monitor System should be posted later this week. Check the CREC Homepage for an announcement and link to this tool perhaps by sometime tomorrow.

FLOWER BUD INDUCTION ADVISORY #5 for 2005-2006-12/29/05

Please review the background information in the first advisory if you have not already done so.

Current Status: Accumulated cool weather has now reached 800 to nearly 1300 hr < 68 degrees F. from southern to northern citrus districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be 80 additional hours below 68 degrees F. during the next 7 days. This means that all areas will in the high to very high range of flowering potential by next week. The 8-day forecast has a warm period starting today. The NOAA forecast predicts 4 to 7 days of warm weather. To view specific FAWN data for a location near you, use https://crec.ifas.ufl.edu/ and click on FAWN, or for NOAA's 8-day forecast go to Weather Links on our CREC homepage and then 8-day forecast.

Since all areas are at fairly high induction levels, this warm period should trigger differentiation of flower buds if soil moisture is adequate for growth. The flowering monitor system indicates that differentiation could have started in the Ona region. Except for Ft. Pierce , FAWN sites in citrus production areas have recorded only traces of rain over the past 14 days (FAWN), soil moisture may be depleted from lower rooting depths in most citrus producing area if restricted irrigation has been managed as we recommended earlier. If you stopped irrigation this week after using shallow irrigations in previous weeks, you may develop drought conditions for this warm period which could inhibit flower buds growth this week. This may be advisable if you want to maintain some cold hardiness for a potential freeze in mid-January or if you wish to delay bloom into mid to late March.

It is now time to worry about excessive flowering. Too many flowers in seedless cultivars (navels), hybrid blocks with a moderate to light crop and some strains of Rhode Red Valencia that set poorly result either in too much flower competition and poor set (navels and some Rhode Reds) or in excessive set (seedy mandarin hybrids) and poor fruit size. A GA 3 spray is advised towards the end of this first warm spell (4 to 5 days exceeding 75 degrees F), note that these temperatures are lower than stated previously because the intensity level of induction is now higher. The above citrus types are likely to have excessive flowering with few leaves associated with the inflorescence. GA 3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. The warm period will persist over New Year's weekend and GA sprays can be effective if used next week. Although flowering potential is probably high enough, if you plan to use either urea or PO3 to enhance flowering, you should apply those sprays immediately. Personally, I would try to slide through a possible warm period at this time by having my trees in drought stress. This is because of the chance of a hard freeze in January.

This is an El Niño Neutral year, which increases the likelihood of a freeze. Generally, a hard freeze is most likely until we get pasted January 15 th to 20 th . If a warm period occurs before that date, some or all of cold hardiness will be lost as the buds start to swell and grow. Being able to create drought stress is one way to prevent loss of cold hardiness. Since the chance of rain on Christmas day apparently occurred only in the Indian River, those who managed irrigation and have now shut down irrigation may prevent loss of cold hardiness over the New Years weekend.

The Web based Citrus Flowering Monitor System is now posted. The link to this tool is: http://orb.at.ufl.edu/DISC/bloom When the Window comes up, click on Run Model, fill in the site and other information and then click on the run model tab below this information. You should see a graph with black line indicating accumulated induction hours and a red line extension for the projected additional induction hours from the NOAA 8-day forecast. You can evaluate any site where FAWN has a weather station (The first pull down information window)

FLOWER BUD INDUCTION ADVISORY #6 for 2005-2006-1/12/06

Please review the background information in the first advisory if you have not already done so.

Current Status: Accumulated cool weather reached 810 to 1250 hr < 68 degrees F. from southern to northern citrus districts, respectively, before the first warm period triggered differentiation of some flower buds starting about 22-27 December, depending on the citrus district. An additional 250 hours of cool weather accumulated before the second warm period that we are now experiencing. The NOAA 8-day forecast predicts cooler weather this weekend and then warming again next week. This should solidify the beginning of differentiation of most flower buds. Evidence of their swelling should be readily visible in the next two weeks, particularly terminal buds. To view specific FAWN data for a location near you, use https://crec.ifas.ufl.edu/ and click on FAWN, or for NOAA's 8-day forecast go to Weather Links on our CREC homepage and then 8-day forecast.

Full bloom is predicted to be the first week of March, with a second wave of flowers by mid-March if most available buds were not induced by the Christmas warm period. If two flowering cohorts do occur, they probably will appear as a prolonged bloom over this two week period. Actual bloom date may change if abnormally warm (earlier bloom date) or cool (later bloom date) weather occurs.

On all healthy, non-hurricane damaged trees, flowering levels should be very good. Too many flowers in seedless cultivars (navels), hybrid blocks with a moderate to light crop and some strains of Rhode Red Valencia that set poorly results in too much flower competition and poor set (navels and some Rhode Reds). On the other hand, too many flowers usually results in excessive set and poor fruit size in seedy mandarin hybrids. A GA 3 spray is advised in these cases by early next week. GA 3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence.

Some growers may still be successfully managing soil moisture and have gotten through the Christmas and current warm periods with their trees under drought stress. When the 8-day forecast looks favorable for no freeze chance through January 25 th , it will be a good time to start irrigation and then to apply the first ground fertilizer for the year.

This is an El Niño Neutral year, which increases the likelihood of a freeze. Generally, a hard freeze is most likely until we get pasted January 15 th to 20 th . If a warm period occurs before that date, some or all of cold hardiness will be lost as the buds start to swell and grow. Being able to create drought stress is one way to prevent loss of cold hardiness.

The Web based Citrus Flowering Monitor System is now posted. The link to this tool is: http://orb.at.ufl.edu/DISC/bloom When the Window comes up, click on Run Model, fill in the site and other information and then click on the run model tab below this information. You should see a graph with a black line indicating accumulated induction hours and a red line extension for the projected additional induction hours from the NOAA 8-day forecast. The black to blue line moving downward with time indicates the progress of flower bud differentiation and bud development to a full bloom date on the x axis. You can evaluate any site where FAWN has a weather station (The first pull down information window), by going back one step to refresh the Run Model Window.

FLOWER BUD INDUCTION ADVISORY #1 for 2004-2005-11/1/04

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

Overview of flower bud induction in Florida – It is time to start following citrus flower bud induction conditions for the coming year's bloom. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate. A period of 5-12 days of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be a weak to moderate El Niño year, cooler and wetter than normal. Even if this winter is only slightly cooler than normal, enough hours of low temperatures below 68 degrees F. should accumulate to induce a moderate to good level of flower buds.

Under normal Florida conditions, sufficient flower bud induction should be achieved when total uninterrupted, accumulated hours of low temperatures exceed 850 hours below 68 degrees F. if the current crop is heavy. If the crop load is light, sufficient flower bud induction can occur after 750 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures > 75 to 80 degrees F., after some low temperatures have accumulated can trigger growth (bud swelling). Fewer days of higher temperatures and lower daytime highs are required to stimulate growth if the accumulated cool temperature hours are high later in the winter. Current and previous seasons weather information is available on the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. The 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt and is linked to http://www.crec.ifas.ufl.edu/crechome/crecweather.shtml

Some flower buds will be induced in the range of 300 to 600 accumulated hrs < 68 degrees F. Warm events after these levels of induction result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods. This situation results in multiple blooms. During the years from 1963 to 2002, multiple blooms occurred in over half of the years. Historically, the time period in which a warm 7-12 day period can lead to some bud growth and then result in multiple blooms is roughly Thanksgiving to Christmas. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is to promote water stress by stopping irrigation before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, mild water stress will have little impact on current crop development or quality. Mild water stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a mild stress condition of citrus trees, buds will not grow in response to high temperatures. If an extended warm period has passed, trees again can be watered to minimize current crop water stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts of cool periods. Therefore, the chances of being able to use water stress to prevent an early flower bud differentiation event is reasonably good for most warm periods. A difficulty that occurred 3 years ago, which resulted in a very small crop, was that daytime high temperatures were continuous through the fall until December 18 th . If trees were allowed to be water stressed for this extended a period, this could lead to low photosynthesis, little fruit growth or sugar accumulation and probably excessive fruit drop.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. This may be risky for ‘Hamlin' or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus'.

(Figure 1, with added information in color or bold lettering, is from the ‘Flowering Expert System for Florida Citrus' and represents the different aspects of apparent flower induction.)

The level of potential flowering would be greater (orange line) with a light crop or less (green line) with a heavy crop for the same amount of hours of induction. Although this representation does not appear on the working screen, recommendations (bottom text box) do consider the current crop level in assessing when action should be taken to try to prevent or to promote initiation of the flower bud growth process. This system will be tested again this winter with several growers that helped us refine the system the past two years. Future advisories (usually weekly) will update accumulating hours of related temperatures and other weather effects on flower bud induction plus methods for enhancing or reducing flowering intensity as conditions and cultivars dictate. Read the archived advisories from previous years (link at top of page) for more background.

Previous 3-year's results – In the winter of 2001-2002 cool temperature accumulation was very slow, warm temperatures persisted and many buds started to grow by 20 December, heavily to vegetative buds. This resulted in few buds remaining for a second flowering wave and a small crop occurred. In the winter of 2003-2003 by late December we had 850 hours of uninterrupted cool inductive temperatures with a low current crop on the trees. The following warm period initiated almost all the buds on all of the spring and summer flush to differentiate and bloom in early March. We had a fairly leafy bloom of very short duration (slightly more than 2 weeks ). In spite of the high temperatures during and following bloom, a good fruit set occurred in other round oranges resulting in the highest October crop forecast for Florida that FASS has ever predicted. Last year (2003-2004), there was good flower bud induction and reasonably good fruit setting conditions, although the heavy previous crop probably reduced flowering levels and set somewhat. Even though fruit size was small, it looked like we were headed for a mid-200 million box orange yield before the hurricanes.

The new season's situation – If you have citrus that was not in the path of the hurricane, two years of heavy to moderately heavy crops means that a high level of induction is desired to produce adequate flower buds for next year's crop. If the block was in the path of one to three hurricanes, then many scenarios exist and most of my conclusions are guess work, but here they are:

If you lost fruit but not many leaves, the trees may need less inductive temperatures, but fruit losses were after most of the summer drain on carbohydrates had occurred. If fall temperatures stay in the mid-70s to low 80s, trees may build up carbohydrate reserves under a low crop situation providing good bud condition for flower induction.

If many leaves were lost along with the crop, then trees may have fairly low carbohydrate levels and need high levels of inductive temperatures to produce a good bloom.

If heavy fruit and leaf loss was followed but many buds stimulated to flush this fall, then fewer buds are available on last year's spring and summer flush for flowering. However, if these fall flushes matures sufficiently before bud growth stimulation occurs (usually in early to late December), then their buds can become flower buds. I think that 2 to 2 ½ months for flush development may be necessary for this to happen.

Therefore, best results this fall-winter may come from reasonable development temperatures until mid-November followed by above average cool temperature accumulation (> 850 hrs).

So far this Fall, little cool weather has occurred to slow down or stop vegetative growth on mature trees, only about 110 to 160 hr < 68 degrees F., from southern to northern districts. Also, the National Weather Service (NOAA) predicts that there will be about 80 more hours below < 68 degrees F. during the next 8 days. To view specific FAWN data for a location near you in the citrus growing areas, use (https://crec.ifas.ufl.edu/) and click on FAWN or for NOAA's 8 day forecast go to Weather Links on our CREC homepage and then 8 day forecast.

The major concerns for the next 60 days are the possibility of 1) continuous warm weather that will push vegetative buds to grow as occurred 3 winters ago or 2) an extended warm period, 10 to 12 days with max. temperatures > 75 to 80 degrees F, following an inductive period of 300 to 500 hrs < 68 degrees F that will initiate differentiation of easily induced flower buds. The first condition will lead to low flowering and the second to multiple blooms. By next week the 200 to 250 total hours will be ½ way to a weak bloom potential. Continued accumulation of cool temperatures or prevention of growth during a winter warm spell are important to a good start to the 2005-06 harvest season. Therefore, keep irrigation amounts low to moderate (if fruit are still present) to minimize growth possibilities. Prepare to keep groves relatively dry, keep track of induction hours in your area and watch for the next advisory.

( Request for potential cooperators) – Although rains this past winter negated attempts to use water stress to delay bloom in many areas and collection of meaningful yields was severely disrupted by the hurricanes, we are still interested in tests to delay bloom by managing irrigation to delay initiation of flower bud growth. This might be accomplished by using water stress to prevent growth during warm winter periods until mid-January has passed. If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin' or ‘Valencia' trees under this protocol.

FLOWER BUD INDUCTION ADVISORY #2 for 2004-2005-11/8/04

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review the background information in the first advisory if you have not already done so.

Current Status: So far this Fall, cool weather has reached 150 to 200 hr < 68 degrees F., from southern to northern citrus districts. Also, the National Weather Service (NOAA) predicts that there will be about 80-90 additional hours below < 68 degrees F. during the next 8 days.

This week's cool weather should bring buds to a rest stage and by the end of next week our major concern will be the possibility of an extended warm period, 10 to 12 days with max. temperatures > 80-85 degrees F, occurring before we have reached an ideal amount of cool temperature flower bud induction. An extended warm spell after an inductive period of 300 to 500 hrs < 68 degrees F will initiate differentiation of easily induced flower buds, and this would lead to an overall weak flowering wave with an early bloom date. Continued accumulation of cool temperatures and prevention of growth initiation during a winter warm spell are important to a good start to the 2005-06 harvest season. Therefore, keep irrigation amounts low to moderate (if fruit are still present) to minimize growth possibilities. Prepare to keep groves relatively dry, keep track of induction hours in your area and watch NOAA's 8-day forecast for possible warm weather that could force initiation of bud growth. Remember this protocol is advised at least until Christmas.

(Request for potential cooperators) – Establishing mild drought stress when warm periods occur through mid-January also might benefit growers by delaying bloom date into mid- to late March as well as compressing the flowering period. Although rains this past winter negated attempts to use water stress to delay bloom in many areas and collection of meaningful yields was severely disrupted by the hurricanes, we are still interested in tests to delay bloom by managing irrigation to delay initiation of flower bud growth. I have received one new positive response to putting some blocks into this protocol. If you are interested in putting one or more blocks or a few rows of grapefruit, ‘Hamlin' or ‘Valencia' trees under this protocol.

FLOWER BUD INDUCTION ADVISORY #3 for 2004-2005-11/15/04

Current Status: As predicted last week, accumulated cool weather has now reached 200 to 300 hr < 68 degrees F. from southern to northern citrus districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be about 80-90 additional hours below < 68 degrees F. during the next 7 days. This means that all areas will be in the low flowering potential level by next week. To view specific FAWN data for a location near you in the citrus growing areas, use ( https://crec.ifas.ufl.edu/ ) and click on FAWN or for NOAA's 8 day forecast go to Weather Links on our CREC homepage and then 8 day forecast.

Up to this week, cool temperature accumulation has been about average compared to the last 4 years. The predicted rate of accumulation for the next 8 days is also average, but an extended warm period the last week of November or in early December would lead to an overall weak flowering wave which would have an early bloom date. Continued accumulation of cool temperatures and prevention of growth initiation during a winter warm period are important to a good start to the 2005-06 harvest season. Therefore, keep irrigation amounts low to moderate (if fruit are still present) to minimize growth potential during a warm period. Prepare to keep groves relatively dry, keep track of induction hours in your area and watch NOAA's 8-day forecast for possible warm weather that could force initiation of bud growth. Remember this protocol is advised at least until Christmas.

 

FLOWER BUD INDUCTION ADVISORY #4 for 2004-2005-11/22/04

Current Status: Accumulated cool weather has now reached 270 to 400 hr < 68 degrees F. from southern to northern citrus districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be about 80-90 additional hours below < 68 degrees F. during the next 7 days. This means that all areas will be in the low to moderate range of flowering potential by next week. To view specific FAWN data for a location near you in the citrus growing areas, use ( https://crec.ifas.ufl.edu/ ) and click on FAWN or for NOAA's 8 day forecast go to Weather Links on our CREC homepage and then 8 day forecast. The weather records for Lake Alfred are somewhat out of line with other areas, warmer, and need to be evaluated further to see if this central area is warmer or the weather records are incorrect.

Up to this week, cool temperature accumulation has been about average compared to the last 4 years. The predicted rate of accumulation for the next 8 days is also average, but an extended warm period in early December would lead to an overall weak flowering wave, which would have an early bloom date. The NOAA 8 day forecast is predicting slightly cooler weather the end of this week. Hopefully, this trend will continue into mid- to late December, but a warm period often occurs up in December.

Continued accumulation of cool temperatures and prevention of growth initiation during a winter warm period are important to a good start to the 2005-06 harvest season. Therefore, keep irrigation amounts low to moderate (if fruit are still present) to minimize growth potential during a warm period. Low to deficit irrigation is recommended now to prepare groves so that drought stress can be imposed quickly if a warm period is predicted. Since temperatures have been fairly high, it would be a good idea to hold off on further irrigation until the cool period starts later this week. Keep track of induction hours in your area and watch NOAA's 8-day forecast for possible warm weather that could force initiation of bud growth. Remember this irrigation protocol is advised until Christmas. We need at least another 4 weeks of cool

FLOWER BUD INDUCTION ADVISORY #5 for 2004-2005-11/29/04

Accumulated cool weather has now reached 320 to 465 hr < 68 degrees F. from southern to northern citrus districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be about 60-80 additional hours below < 68 degrees F. during the next 7 days. This means that all areas will still be in the low to moderate range of flowering potential through this week, but the accumulated hours will be past the midway point in that category for all citrus areas and some northern areas should be near the break point of 600 hours. To view specific FAWN data for a location near you in the citrus growing areas, use ( https://crec.ifas.ufl.edu/ ) and click on FAWN or for NOAA's 8 day forecast go to Weather Links on our CREC homepage and then 8 day forecast. The cool weather accumulation for Lake Alfred is still below that of Immokalee.

Up to now, cool temperature accumulation has been about average compared to the last 4 years. It is lower than in 2002 but higher than last year. The predicted rate of accumulation for the next 8 days is lower than it has been the previous 2 weeks. Many areas had enough rain over the long weekend to provide adequate soil moisture for bud growth if an extended warm period occurs in early December. Hopefully, the root zone will dry down enough by next week to prevent growth if temperatures warm up by then. The NOAA 8 day forecast is predicting slightly cooler weather the end of this week. Hopefully, this trend will continue into mid- to late December, but remember that a warm period often occurs in December.

Continued accumulation of cool temperatures and prevention of growth initiation during a winter warm period are important to a good start to the 2005-06 harvest season. Therefore, keep irrigation amounts low to moderate (if fruit are still present) to minimize growth potential during a warm period. Low to deficit irrigation is recommended now to prepare groves so that drought stress can be imposed quickly if a warm period is predicted. Since temperatures have been fairly high and some rainfall occurred this past weekend in many areas, it would be a good idea to hold off on further irrigation this week and wait to see what next week will bring. Keep track of induction hours in your area and watch NOAA's 8-day forecast for possible warm weather that could force initiation of bud growth. Remember this irrigation protocol is advised until Christmas. We need at least another 3 to 4 weeks of cool weather to be in a good position regarding flower bud induction (+ 800 hours). Try not to let a warm period break the process.

For trees not affected by the hurricanes and producing a good crop for the second year in a row, it may take near 900 hours < 68 degrees F. to provide adequate flower bud induction. Since temperature highs on most days the past two months have been near 80 degrees F. or higher, trees with fall flush due to leaf loss from one or more hurricanes have had time to mature much of the fall flush. This means that these trees should have adequate flower buds if the cool weather continues. It is particularly important for these trees that cool temperature accumulation continues to a high level (approaching 900 hours < 68 degrees F.). Therefore, this winter in Florida all trees would do better if higher levels of flower bud induction occurred than are normally required.

FLOWER BUD INDUCTION ADVISORY #6 for 2004-2005-12/6/04

Current Status: Accumulated cool weather has now reached 400 to nearly 600 hr < 68 degrees F. from southern to northern citrus districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be about 80-83 additional hours below < 68 degrees F. during the next 7 days. This means that all areas will be in the upper part of the low to moderate range of flowering potential by next week, and the cooler districts should reach the first stage of the moderate to high range, exceeding 600 hours. The NOAA forecast for the coming week is a continued increase in cool hours with the first 3 to 4 days having daytime highs in the lower 80s, followed by 3 days with highs in the lower 70s. To view specific FAWN data for a location near you in the citrus growing areas, use ( https://crec.ifas.ufl.edu/ ) and click on FAWN, or for NOAA's 8 day forecast go to Weather Links on our CREC homepage and then 8 day forecast.

Up to now, cool temperature accumulation is still about average compared to the last 4 years. It is lower than in 2002 but higher than last year. The predicted rate of accumulation for the next 8 days is higher than it has been the previous 2 weeks. Rain is predicted towards the end of this week, followed by cooler weather. Don't irrigate this week until you see how much rain you get and if the cool period materializes. We need the NOAA predicted cooler weather the end of this week to continue into mid- to late December. Remember that a warm period often occurs in December and the terminal buds on spring and summer shoots are now easily stimulated to initiate growth by a warm period (probably 5 to 7 days in the mid-80s) if soil moisture is adequate for flower buds to initiate growth.

Continued accumulation of cool temperatures and prevention of growth initiation during a winter warm period are important, therefore, keep irrigation amounts low to moderate (if fruit are still present) to minimize growth potential during a warm period. Soil moisture below 50 to 60 % depletion is probably necessary to prevent bud growth. Low to deficit irrigation is recommended now to keep groves near drought stress if a warm period is predicted. Since temperatures have been fairly high and some rainfall occurred this past week in many areas, it would be a good idea to hold off on further irrigation this week and wait to see what the end of the week will bring. Keep track of induction hours in your area and watch NOAA's 8-day forecast for possible warm weather that could force initiation of bud growth. Check the NOAA forecast at least every other day so that you don't get surprised by a warm period. Remember this irrigation protocol is advised until Christmas. We need at least another 3 to 4 weeks of cool weather to be in a good position regarding flower bud induction (+ 800 hours). Try not to let a warm period break the process.

For trees not affected by the hurricanes and producing a good crop for the second year in a row, it may take near 900 hours < 68 degrees F. to provide adequate flower bud induction. Since temperature highs on most days the past two months have been near 80 degrees F. or higher, trees with fall flush due to leaf loss from one or more hurricanes have had time to mature much of the fall flush, perhaps excepting flush after Hurricane Jeanne. This means that these trees should have adequate flower buds if the cool weather continues. It is particularly important for these trees that cool temperature accumulation continues to a high level (also approaching 900 hours < 68 degrees F.). Therefore, this winter in Florida all trees would do better if higher levels of flower bud induction occurred than are normally required.

It is time to start thinking about flower induction enhancing sprays (urea or phosphorous acid (PO3)). They will be most useful if a warm period is predicted from near to shortly after Christmas and the total hours < 68 degrees F. has not reach 850 hours. Trees with severe defoliation from hurricanes this summer may not be good candidates for these sprays this winter since there will not be as much surface area available to catch the spray. If direct contact with the buds is sufficient, it will not matter if few leaves are present. Unfortunately I don't know the answer to the question, ‘Which tissue needs to be present to absorb the spray material?' (another hurricane puzzle). Anyway, if you are anticipating spraying one of these products, be sure you have material on hand. For urea, you need 53 to 60 lbs of urea available per acre you plan to treat. For a PO3 product you need 3 pints to 2 quarts per acre depending on which product you use (60 % P (3pts) or if 26 % P (2 qts) product)

FLOWER BUD INDUCTION ADVISORY #7 for 2004-2005-12/13/04

Accumulated cool weather has now reached 470 to nearly 700 hr < 68 degrees F. from southern to northern citrus districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be about 120 to 168 additional hours below < 68 degrees F. during the next 7 days. This means that all areas will be in the moderate to high range of flowering potential by next week, and the cooler districts should reach the mid-point of this range. The NOAA forecast for the coming week is generally for all temperatures to be in the inductive range, although some northern areas will have a few hours below the effective range (<40 degrees F.) and the Gulf region may have a few hours above the effective 68 degrees F. A freeze is not predicted, but citrus areas from Central to Northern Districts may have temperatures near 32 degrees F. Wednesday morning according to NOAA. To view specific FAWN data for a location near you in the citrus growing areas, use ( https://crec.ifas.ufl.edu/ ) and click on FAWN, or for NOAA's 8 day forecast go to Weather Links on our CREC homepage and then 8 day forecast.
Up to now, cool temperature accumulation has been about average compared to the last 4 years. The predicted rate of accumulation for the next 7 days is higher than normal for this time of year. Most areas received some rainfall this past week, but if not, light irrigation this week is safe as buds will be held in check by the cool weather. If this week's predicted weather continues for the following week, central to northern areas will be near 900 hours < 68 degrees F. Southern areas will need another week after that to reach that goal. If a warm period occurs before then and soil moisture is adequate, the terminal buds on spring and summer shoots are now easily stimulated to initiate growth. As of today, the model does not indicate that a wave of buds has started to initiate growth after the warm days that just ended. The Immokalee area had a 6-day period with daily highs from 82-85 in November and 5 days of 81 to 85 in December, but these periods were separated by a cooler period. Other areas had cooler daytime highs.
Low to deficit irrigation is still recommended now to keep groves near drought stress if a warm period does occur before three more weeks of cool temperature accumulation. Keep track of induction hours in your area and watch NOAA's 8-day forecast for possible warm weather that could force initiation of bud growth. Check the NOAA forecast at least every other day so that you don't get surprised by a warm period. Remember this irrigation protocol is advised until Christmas. We need at least another 2 to 3 weeks of cool weather to be in a very good position regarding flower bud induction (+ 900 hours). Try not to let a warm period break the process.
See last week's advisory about hurricane affected trees and their flowering potential. Also look at last week's advisory about planning for urea or PO3 sprays to enhance flowering. If the cool weather continues until we reach 900 hours < 68 degrees F., the need for using one of these sprays will be greatly diminished. Weak blocks might be more likely to respond. If a warm period occurs in the next 2 (northern) or 3 (southern areas) weeks, then it is the time to spray. This provides a window of about 7 days to cover the areas you decide on before bud development has advanced too far.

FLOWER BUD INDUCTION ADVISORY #8 for 2004-2005-12/20/04

Accumulated cool weather has now reached 620 to 850 hr < 68 degrees F. from Southern to Northern Citrus Districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be about 110 to 140 additional hours below < 68 degrees F. during the next 7 days. This means that all areas will be above the mid-point of the moderate to high range of flowering potential by next week, and the northern areas will reach the high range. The NOAA forecast for the coming week again is generally for all temperatures to be in the inductive range, although two cold fronts (Tuesday and Saturday) may produce a few hours below the effective range (<40 degrees F.). The coldest front is expected to be at or near freezing in Central to Northern Districts. Go to http://www.wunderground.com/US/Region/US/JetStream.shtml and follow the jet-stream pattern tonight. If we maintain lateral flow off the Gulf, we should avoid a hard freeze. If the north to south jet-stream flow becomes stronger than the lateral flow, watch out. As of 6 am Monday, the flow pattern looked favorable. Check it again this evening. To view specific FAWN data for a location near you in the citrus growing areas, use ( https://crec.ifas.ufl.edu/ ) and click on FAWN, or for NOAA's 8 day forecast go to Weather Links on our CREC homepage and then 8 day forecast.

Trees are now making very good progress towards accumulating sufficient cool temperature induction. The predicted rate of accumulation for the next 7 days is higher than normal for this time of year. If this week's predicted weather continues for the following week, central to northern areas will be above 900 hours < 68 degrees F. Southern areas will reach the 900 hour goal with another week of cool weather between Christmas and New Year. If a warm period occurs that week and soil moisture is adequate, the terminal buds on spring and summer shoots will be easily stimulated to initiate growth. The model still does not indicate that a wave of buds has started to initiate growth after the warm days in early December. We are on track to have a single intense bloom in most areas and likely in all areas if the weather stays cool through New Year's day.

A warm period in late December or early January will initiate bud growth for a bloom in early March. Several growers will be trying to delay that growth by maintaining low to deficit irrigation through any warm periods until late January. This should result in a late March bloom date. Keeping groves near drought stress will prevent bud growth if a warm period does occur before then.

Keep track of induction hours in your area and watch NOAA's 8-day forecast for possible freezes or warm weather that could force initiation of bud growth. Check the NOAA forecast at least every other day for development of either condition.

See earlier advisories about hurricane affected trees and their flowering potential (return bloom now looks promising). Also look at earlier advisories about planning for urea or PO3 sprays to enhance flowering. The need for using one of these sprays is greatly diminished. Weak blocks might be more likely to respond, particularly in southern areas. If used, these sprays should be applied as the weather warms up at the first warm period, and you can have effective results until 3 or 4 days into the warm period. Usually, this provides a 7 day spray window for these applications. If cool temperatures last through the first week of January, it is not likely that these sprays will be beneficial since a very good level of natural flower bud induction will have been reached..

FLOWER BUD INDUCTION ADVISORY #9 for 2004-2005-12/27/04

Please review the background information in the first advisory if you have not already done so.
Accumulated cool weather has now reached 733 to 1015 hr < 68 degrees F. from Southern to Northern Citrus Districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be an additional 83-100 hours below < 68 degrees F. during the next 7 days. This means that all areas, except the Indian River District, will be in the high range of flowering potential by next week. The NOAA forecast for the coming week is generally for daytime temperatures to be in the upper 70s by Thursday or Friday. To view specific FAWN data for a location near you in the citrus growing areas, use ( https://crec.ifas.ufl.edu/ ) and click on FAWN, or for NOAA's 8-day forecast go to Weather Links on our CREC homepage and then the 8-day forecast.
It now appears that all districts will accumulate at least 900 hours < 68 degrees F. before a sufficient warm period occurs to initiate flower bud growth. This should be a good level for flowering under our current situation. Look at previous advisories for discussion of tree conditions this year. All areas received some rainfall over the Christmas weekend with Central to Northern Districts getting 1 to 2 inches. According to the FAWN system, most Southern areas received .5 to 1 inch. In general, soil moisture currently is sufficient for bud growth. If the predicted warming trend the end of this week occurs and continues into next week, bud growth will likely be initiated sometime next week. Blocks that received no more than .5 inches of rain may dry out enough to be in enough drought stress next week to avoid initiation of bud growth. If the weather stays cool enough into next week, all areas may avoid initiation of bud growth next week. At the current high level of induction, five or six days near 80 degrees should initiate flower bud growth. If the warming trend does persist, only areas with low rainfall this past weekend are good candidates for delayed bloom by continuing to withhold irrigation.
For blocks that you wish to supplement bud induction with a urea or PO3 spray, the projected warmer weather may be the time to apply these sprays. Temperature for good spray uptake should be in the 70s. Unfortunately, these temperatures are projected for Thursday or Friday (Could ruin your New Year's weekend if you need to spray large acreages). If by Thursday, the 8-day forecast or your local weather news (5 or 6 day forecast) projects temperatures continuing above 75 degrees each day, then initiation of bud growth is likely. All sprays should then have been applied by the middle of next week.

FLOWER BUD INDUCTION ADVISORY #10 for 2004-2005-1/3/05

It has happened! The flowering model indicates that initiation of flower bud differentiation has started in most areas, probably all. Accumulated induction hours were at 820 to 830 hours < 68 degrees F. from South to North when the process started on December 22 or 23 (about 9 days ago).
Two areas, Ft. Pierce and Lake Alfred don't show initiation to have started, but this may be due to incorrectly monitored low induction hours indicated by FAWN, particularly for Lake Alfred. These two areas currently have 840 and 973 hr < 68 degrees F., respectively. Accumulated cool weather to date has reached 840 to 1150 hr < 68 degrees F. from Southern to Northern Citrus Districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be an additional 80 hours below < 68 degrees F. during the next 7 days. These hours may affect some additional buds during the transition period or add to the potential for a second wave of flowering. However the prolonged warm period is still on us and is likely to push most buds into flowering or vegetative shoot growth. The NOAA forecast for the coming week is for daytime temperatures to be in the upper 70s to low 80s. To view specific FAWN data for a location near you, use ( https://crec.ifas.ufl.edu/ ) and click on FAWN, or for NOAA's 8-day forecast go to Weather Links on our CREC homepage and then the 8-day forecast.
I was hoping we would reach 900 hrs < 68 degrees F. before the initiation of flower bud growth, but many areas did not achieve this. Most Central to Northern Districts received 1 to 2 inches of rainfall over the Christmas weekend, while most Southern areas received < .5 to 1 inch. Soil moisture is sufficient for bud growth in most citrus areas so the indicated initiation has occurred where the root zone is wet. For Central to Southern areas, blocks that had or still have a good current crop may benefit from a urea or PO3 spray to enhance bud induction. Three to 4 days remain in which these sprays may be effective. Daytime temperatures, in the 70s, will be good for spray uptake.
Blocks that received less than .5 inches of rain may be dry enough now to have drought stress, which will prevent the current initiation of bud growth. These potential blocks for delayed bloom can be evaluated by looking for leaf wilting by 11 am to noon. With the continuing warming trend, only areas with low rainfall over Christmas are good candidates for delayed bloom by continuing to withhold irrigation. Examine the first two buds from the apex of summer shoots by hand lens to see if they are swollen compared to buds 6 or 7 leaves down. If no buds are swollen, initiation has not started and drought stress will continue to prevent it.

FLOWER BUD INDUCTION ADVISORY #11 for 2004-2005-1/10/05

Its still happening! The flowering model indicates that initiation of flower bud differentiation has started in all areas. Accumulated induction hours were at 830 to 1130 hours < 68 degrees F. from South to North when the process started on December 30 th (Ft. Pierce, December 22 nd or 23 rd in southwestern areas, December 25 th in central areas and December 30 th in northern areas. Swell of shoot apex buds has been confirmed in Ft. Pierce and Lake Alfred.
Two locations for which the model did not show initiation of differentiation last week, Ft. Pierce and Tavares, were probably behind because of lower induction hours at Ft. Pierce and lower daytime temperatures at Tavares. Lake Alfred might have been delayed due to both conditions. Bud swell was not detected in Lake Alfred until the middle of last week, somewhat confirming the model results. Since the start of flower bud differentiation, another 100 to 250 hours of induction conditions have accumulated. The program further predicts, using National Weather Service (NOAA) data, that there will be an additional 60 to 120 hours below < 68 degrees F. during the next 7 days. These hours may cause enough additional buds to be induced to flower for a second wave of flowering. However, the level of induction for the first wave of buds was fairly high (839-1100), and I expect most available buds to be in the first wave of flowering. To view specific weather data for a location near you, use ( https://crec.ifas.ufl.edu/ ) and click on FAWN, or for NOAA's 8-day forecast go to Weather Links on our CREC homepage and then the 8-day forecast. Additional weather data links are also listed.
From available rainfall data, it appears that only the area around Clewiston, LaBelle and Immokalee had low enough rainfall (< .5 inches) during the Christmas weekend for trees to have been in drought stress, and therefore for initiation of flower buds not to have started during the prolonged warm period that is currently visiting us. Any trees in that general area that were well irrigated did start the initiation of flowering. Examine the first two buds from the apex of summer shoots by hand lens to see if they are swollen compared to buds 6 or 7 leaves down. If no buds are swollen, initiation has not started and drought stress will continue to prevent it until the trees are irrigated or a rain rewets the soil. These blocks for potential delay of bloom should be showing leaf wilting by 11 am to noon. The NOAA forecast for the coming week has daytime temperatures still in the upper 70s to low 80s through Friday and then a cool front with potential for rain will drop daytime highs into the 60s (northern half of citrus areas) to low 70s (southern half). The cooler weather may last for at least the following week.
With the long warming trend, only trees in areas with low rainfall over Christmas are good candidates for delayed bloom by continuing to withhold irrigation. If sufficient rain occurs this coming weekend in the southern area, flower bud differentiation may start when temperatures again are in the mid to high 70s. If the cool period next week is mostly below 70 degrees F and long enough for soil moisture to again be depleted, then bud growth may again be prevented during the next warm period. In order to produce later maturing, higher solids fruit as a response to later flowering, I think it will be desirable for the flower bud growth process not to start until after January 20th.
Currently general bloom dates are projected from late February through March 4 th . In some cases this is one to two days earlier than projected one week ago. The continued warm weather this week may further shorten the time to the estimated bloom date.
Many people are reporting very hard looking trees in the hurricane path, particularly the fall flush stimulated by leaf loss. Flowering on this flush may be reduced because of low carbohydrate and nutrient levels. Fruit set may also be impacted. It will be very important to start this year's nutritional program on these impacted trees early in order to have good nutritional levels in the tree at least 2 weeks before the projected late February, early March bloom date.
While nutritional programs are becoming very important for next years crop, I think it is now too late to get any benefit by enhanced flowering from foliar sprays of urea or PO3.

 

FLOWER BUD INDUCTION ADVISORY #12 for 2004-2005-1/17/05

Some interesting things are happening according to the flowering monitoring system! The model indicates that initiation of flower bud differentiation has started for 2 waves of flowering in lower central areas from Sebring through Ona, but not in the Ft. Pierce or Immokalee areas nor from Lake Alfred north. The second wave of flowering for the central areas is based on accumulated induction hours of only about 200 additional hours since the first wave started. This appears to be a small change that should not result in a significant second wave of flowers. Further, the bloom date difference is only 2 weeks, which will not be noticeable. The total accumulated hours < 68 degrees F were at 989 to 1376 hours < 68 degrees F. from South to North as of today. Considering that this week will be very cool an additional 300 to 400 hours will have accumulated by next Monday since the first wave of flower bud differentiation started. These hours will contribute to a second flowering wave for the southern and northern areas. Because of either heavy crops or hurricane leaf loss induced fall flush, trees are likely to respond with a second flowering wave when temperatures warm up after this cool period.
To view specific weather data for a location near you, use ( https://crec.ifas.ufl.edu/ ) and click on FAWN, or for NOAA's 8-day forecast go to Weather Links on our CREC homepage and then the 8-day forecast. Additional weather data links are also listed.
From available rainfall data, it appears that only the area around Clewiston, LaBelle and Immokalee had low enough rainfall (< .5 inches) this past weekend for trees to have remained in drought stress, and therefore for initiation of flower buds not to have started during the prolonged warm period that occurred until this weekend. Any trees in that general area that were well irrigated did start the initiation of flowering and are projected to be in full bloom on February 28 th . For those in this southern area that have been maintaining drought stress by withholding irrigation, trees should start to receive water when the weather warms up after this cool period. Trees will then probably bloom in late March rather than late February. To be sure that trees have not started initiation of flower bud differentiation, check apex lateral buds for swelling compared to basal buds on summer shoots.
Currently general bloom dates are still projected from late February through March 4 th . The second wave of flowering projected by the flowering monitoring system should be at full bloom on March 14th.
Heavy crops the last two years and hurricane induced leaf loss have left many trees low in carbohydrates and nutrients. Soil applied nutritional programs should be started by early February to have nutrients in the tree at least 2 weeks before the projected early March bloom date. While good nutritional programs are especially important for next years crop, I think it is now too late to get any benefit of enhanced flowering in the first initiation wave of flower buds from foliar sprays of urea or PO3. The projected second wave of flowering in southern citrus production areas could be enhanced by a foliar spray of urea or PO 3 applied at the end of this current cool period. This is a hard decision to make as there may be enough flowers in the first wave for an economic crop. For anyone choosing to do either of these sprays, the timing rules discussed in previous advisories apply regarding early in the next warming period. At the same time, navel blocks may have too many flowers if this second flowering wave occurs. A spray of 10 ppm GA 3 applied at the beginning or up to 5 days into the next warming period can diminish the flowering level (see EDIS report HS-799, listed and quick-linked at the top of this page).

FLOWER BUD INDUCTION ADVISORY #13 for 2004-2005-1/24/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

All citrus areas now appear to have a second wave of flowering based on the ‘Citrus Flowering Monitoring System'. However by District, the second wave is presumably occurring after only an additional 120 to 230 hours of accumulated hours < 68 degrees F., and the bloom date difference between the first and second wave is only 2 weeks, which will not be noticeable. As of today the total accumulated hours < 68 degrees F are now from 1140 to 1530 hours from South to North. Also the cool temperatures this week will add an additional 80-100 hours resulting in a total of 400 to 500 induction hours since the first wave of buds started differentiation.

When warmer temperatures occur from Wednesday to Thursday this week, this could start another wave of flower bud differentiation. Because of either heavy crops or late fall flush induced by leaf loss during the hurricanes, trees may respond with another flowering wave that would bloom in late March or early April. The buds on the late fall flush needed at least 2 months of warm weather to mature so that the buds could respond to the induction temperatures. Some of the later fall flush may not have had time to accomplish that by the late December warm period.

Buds that would start to differentiate later this week would result in a late March bloom. These and buds that are already growing should have good tree water conditions from now through fruit set. Irrigation should commence as this warm period begins Wednesday or Thursday. Ideally fertilization should occur soon also, at least by early February, so that new nutrients are in the tree 2 weeks before the anticipated late February bloom.

Currently general bloom dates are still projected from February 26 th through March 12 th for the first wave of flowering from Southern to Northern locations. A second wave of flowering is projected to occur from March 16 th to March 20 th by the flowering monitoring system. There should be no additional flowering after the possible third wave mentioned earlier and projected for late March.

To view specific weather data for a location near you, go to FAWN or to NOAA's 8-day forecast in the Weather Links on this CREC homepage ( https://crec.ifas.ufl.edu/ ). Additional weather data links are also listed.

FLOWER BUD INDUCTION ADVISORY #14 for 2004-2005-1/31/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS

The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review the background information in the first advisory if you have not already done so.

Will we have a third wave of flowering? A warm period started the 25 th to 26 th of January and by its end should be enough warm weather to initiate a third flowering wave if induced flower buds are still available. I think there is some possibility of this, particularly for hurricane affected trees that had a heavy fall flush. Generally, the initiation of differentiation of this wave of flower buds would come after flower bud induction from 1250 to 1450 hours of accumulated hours < 68 degrees F.. The bloom date would be around the first of April. By next week, the ‘Citrus Flowering Monitor System' should indicate if it detects the proper conditions for a third wave of initiated flower buds and the projected full bloom date.

All of you that have been looking are seeing the feather push of the new growth in the first 3 to 4 buds from the apex on summer and spring shoots. Flowers are evident, but it is too early to decide if there are enough. I have seen one example of 6 flowers with leaves. Hopefully, most buds will have 2 or 3 flowers with some associated leaves. Currently general bloom dates are still projected from February 26 th through March 12 th for the first wave of flowering from Southern to Northern locations. The second wave of flowering is projected to occur from March 14 th to the 20 th by the Citrus Flowering Monitor system. There should be no additional flowering after the possible third wave mentioned earlier and projected for late March to early April

To view specific weather data for a location near you, go to FAWN or to NOAA's 8-day forecast in the Weather Links on this CREC homepage ( https://crec.ifas.ufl.edu/ ). Additional weather data links are also listed.

FLOWER BUD INDUCTION ADVISORY #15 for 2004-2005-2/7/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS

The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review the background information in the first advisory if you have not already done so.

The ‘Citrus Flowering Monitor' system does not indicate that there will be a third wave of flowering, but only two. The two initiation of differentiation periods came after 830-1100 and 940-1250 accumulated hours < 68 degrees F. from southern to northern citrus areas. The corresponding projected bloom dates are 2/25 to 3/14 and 3/15 to 3/22, respectively for the first and second full bloom dates of each wave.

This is the first time in the past 3-4 years that there has been a 2-week spread in projected bloom dates from southern to northern citrus areas. Since the two waves are predicted to be about 18 days apart, the bloom period will appear to be prolonged and not discrete blooms.

Because of the unusual conditions this year leading to a strong fall flush, I am not at all certain that the ‘Citrus Flowering Monitor' will accurately project the behavior of flushes during that period. The difference in flowering dates predicted by the program for the various citrus districts is also something new to watch.

Since the buds are pushing and the bloom dates are soon, we will not have long to wait before seeing the accuracy of the predicted bloom behavior. There is still a good possibility that fall flush after Jeanne may respond late or not at all. Trees in the Immokalee area that were kept dry from Christmas through early January are also likely to bloom later. The ‘Citrus Flowering Monitor' was not programmed for either of these circumstances.

To view specific weather data for a location near you, go to FAWN or to NOAA's 8-day forecast in the Weather Links on this CREC homepage ( https://crec.ifas.ufl.edu/ ). Additional weather data links are also listed.

While I am traveling on another project, the flowering advisories may be off schedule for the next two weeks. I should have email and still get out some kind of a report about weekly.

FLOWER BUD INDUCTION ADVISORY #16 for 2004-2005-2/14/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS

The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

There has been little change in the predicted bloom dates for citrus trees in the various production areas of Florida. Southern areas should still have full bloom in late February and central areas in early March. Northern areas are now projected to be a little later March 15 th ). The second wave of flowers will be out in mid March in all areas except the north, where the second wave of flowers is expected about March 23rd.

I am away for two weeks, and I don't have a report of the condition of buds on the late fall flushes that occurred after the hurricanes. I should be able to summarize observations on these late flushes in two weeks after I return.

While visiting our citrus producing neighbors to the south, I am observing that they have had their flowering problems this year also. The southern production areas of Brazil's Sao Paulo State had rains with cool temperatures last winter and a good, normal bloom. The northern areas were wet but warm and did not get any flowering at the beginning of the spring period. Flowering did not occur until after the rains stopped, 2 months of drought occurred and then rains started tree growth. This will lead to two different harvesting periods for northern and southern citrus production areas. Most of the healthy trees in the north now have a good crop..

FLOWER BUD INDUCTION ADVISORY #17 for 2004-2005-2/21/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS

The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Predicted bloom dates for citrus trees in the various production areas of Florida are perhaps a day or two earlier than previously expected. For processing oranges, southern areas should have full bloom from 24 to 26 February and central areas about 4 March. Northern areas are projected to be a little later March 15 th . The second wave of flowers will be out in mid March in all areas except the north, where the second wave of flowers is expected about March 23 rd . Navels oranges should be in full bloom about 6 to 7 days earlier and small flowered mandarins about 6 days later than most round orange cultivars.

Please report any confirmations or differences of these bloom dates in your area. For locations in the southern areas where maintenance of drought stress may have been successful, please note if the early bloom date was avoided or diminished and when the major bloom occurred.

FLOWER BUD INDUCTION ADVISORY #18 for 2004-2005-2/28/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS

The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review the background information in the first advisory if you have not already done so

Observations and reports from several people in the industry indicate that the first wave of flowers is occurring about on schedule, perhaps 3 or 4 days later than predicted by the ‘Citrus Flowering Monitor' system (see earlier advisories for dates in your area). However, the amount of flowers in the first wave is highly variable. Very weak, diseased, trees have a good bloom and ahead of predicted bloom dates (February 25-March 5 th ). Some blocks have a good first wave of flowers, but often flowers with few leaves, while other trees are showing almost no flowers. These differences may often relate to the crop load the past two years. Heavy cropping trees may have very low flower counts in this first wave.

Most trees have a second wave of buds pushing out that are maybe 3 to 5 mm in length. Flowering in this wave is not known at this point. Buds on fall flush are out enough to see some flowers if the flush occurred just after the first two hurricanes. Late fall flush after Hurricane Jeanne is just now pushing in the River District and flowering is not determined. By next week, the amount of flowering should be clearer. It does not look like flowering levels will be very high in some blocks unless the second wave is much better than the first. In some cases this may be due to two heavy crops and in others, the hurricanes and leaf loss also may be involved.

Flowering of trees with continuous winter drought in the southern area around LaBelle and Immokalee appear to be significantly behind for time of flowering compared to well irrigated blocks. These growers are reporting a projected bloom date after March 15 th and apparently one wave of flowers. The level of flowering and full bloom date still need to be assessed.

To view specific spring weather data for a location near you, go to FAWN or to NOAA's 8-day forecast in the Weather Links on this CREC homepage https://crec.ifas.ufl.edu/. Additional weather data links are also listed.

FLOWER BUD INDUCTION ADVISORY #19 for 2004-2005-3/7/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS

The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Please review the background information in the first advisory if you have not already done so.

The first wave of flowers has occurred about on schedule as predicted by the ‘Citrus Flowering Monitor' system (see earlier advisories for dates in your area). The full bloom date might be 3 or 4 days later than predicted. This has occurred the last 3 years.

After traveling to several groves this past week, it is even more obvious that the amount of flowers in the first wave is highly variable. Very weak, diseased, trees have a good bloom that opened ahead of predicted bloom dates (February 25-March 5 th ). Some other blocks have a good first wave of flowers, but often flowers with few leaves, while other trees or whole blocks of trees are showing almost no open or popcorn stage flowers.

Most trees have a second wave of buds pushing out that may now be an inch or more in length. In most groves and blocks visited, there are a number of flowers in this wave. This wave should be in full bloom about mid-March. Buds on fall flush are out enough to see flowering when the flush occurred just after the first two hurricanes. Late fall flush after Hurricane Jeanne is now pushing in the River District and some flowering is reported on this flush as well. Trees that had heavy leaf loss are flushing from adventitious buds on older wood (2 or 3 year old and up to thumb diameter). Flowers are present in some of this flush. Flowering in hurricane affected, structurally sound grapefruit trees looks good. It remains to be seen if these flowers will set well on trees without a full canopy of mature leaves.

Heavy cropping and hurricane leaf loss may be responsible for very low flower counts with few leaves in the first wave and heavier flowering in the second wave. The 3 to 4 day delay in full bloom compared to the model this year and the previous 2 years also may be due to heavy crop loads, which are known to delay bloom. Adjustments for crop load effects on intensity and date of flowering are now planned for the ‘Citrus Flowering Monitor' system.

Flowering of trees with continuous winter drought in the southern area around LaBelle and Immokalee appear to be significantly behind for time of flowering compared to well irrigated citrus. A projected bloom date is late in March with one wave of flowers. Further evaluation of these conditions is needed.

To view specific spring weather data for a location near you, go to FAWN or to NOAA's 8-day forecast in the Weather Links on this CREC homepage ( https://crec.ifas.ufl.edu/ ). Additional weather data links are also listed. If you have any questions about bud growth initiation and flowering.

FLOWER BUD INDUCTION ADVISORY #20 for 2004-2005-3/17/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS 

The following information has been developed as part of the Decision Information System for Citrus. 
L. Gene Albrigo, Horticulturist 
Citrus Research & Education Center, Lake Alfred, FL

Please review the background information in the first advisory if you have not already done so.

Bloom dates of the different waves of developing flower buds are almost on schedule with the ‘Citrus Flowering Monitor' model. The unexpected difference is that for most blocks of trees the first wave had few flowers compared to the second wave, which will be the large bloom. For the past 5 or 6 years of careful evaluation, the first wave of flowers has always been the heaviest, if not the only bloom (2 years). Although no data was taken previously, I don't recall a similar situation ever occurring. The actual bloom dates are about 5 or 6 days behind the prediction, maybe partly due to cool weather and partly due to either a heavy previous crop or leaf loss from the hurricanes. Trees in south Florida that were drought stress during the winter will bloom the end of March as predicted in an earlier advisory.

Prior to 10 years ago, the average bloom date was 15 to 20 March. The past few years it has been 1 March or earlier for the first wave. This year would not have been that much different if the first wave had been strong. It appears that late winter through spring temperatures have been warmer in recent years, but the weather data has not been analyzed to see if there has been a significant difference for the 1960s and 70s compared to the past 10 years.

I expect that this year's bloom dates will put us on a more favorable maturation schedule with processing Hamlins not reaching 14-16 ratios until mid-December or later and Valencias holding on later also. Of course fresh fruit harvests should be later also, but with less chance of early section drying. The weather for the rest of the spring and fall will of course affect rate of maturation, but the starting date is important.

To view specific spring weather data for a location near you, go to FAWN or to NOAA's 8-day forecast in the Weather Links on this CREC homepage https://crec.ifas.ufl.edu/. Additional weather data links are also listed. If you have any questions about bud growth initiation and flowering.

FLOWER BUD INDUCTION ADVISORY #21 for 2004-2005-3/22/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS 

The following information has been developed as part of the Decision Information System for Citrus. 
L. Gene Albrigo, Horticulturist 
Citrus Research & Education Center, Lake Alfred, FL

Please review the background information in the first advisory if you have not already done so.

Bloom dates of the different waves of developing flower buds are as confusing as I can remember. Locally, we had a first wave and now have a lot of flowers ready to pop and some to many open depending on the tree, but there are a lot of flowers dragging behind that will not be open before next week. I think it is as much the cool weather as anything else, but the hurricanes and two years of heavy fruit set may be contributing.

I thought the weather might have been warm enough in southern areas to push the bloom out and provide a more concise second wave of flowers. Two reports from that area suggest it is just like here. At least three waves of flowering are being seen. Use of prolonged low irrigation did not result in one late bloom, but rather a delay of the three waves. Perhaps the drought stress level was insufficient to actually stop early bud development. It looks like everyone will still have flowers opening next week. In Desoto County they haven't had enough open flowers to be able to smell the typical orange bloom period. A week of warm weather should really push the pin head flowers along to full bloom. The 8-day forecasts have mid- to high 80s predicted for the latter part of this week as far north as Central Florida. Northern areas may only reach the high 70s. Second wave peak looks like it will be at least 1 to 1 ½ weeks later than the model predicted, which was March 15th.

Dr. Timmer thinks most blocks are ok from PFD if you haven't seen any to speak of yet. However if rains continue this week as predicted and occur again next week, there could be problems if a little PFD is showing this week. You should follow his website and the PFD model recommendations (www.crec.ifas.ufl.edu/timmer).

To view specific spring weather data for a location near you, go to FAWN or to NOAA's 8-day forecast in the Weather Links on this CREC homepage https://crec.ifas.ufl.edu/. Additional weather data links are also listed.

FLOWER BUD INDUCTION ADVISORY #22 for 2004-2005-4/4/05

Please review the background information in the first advisory if you have not already done so.
The bloom period is almost over. Locally, mandarin trees still have some popcorn stage flowers, but most are open. Only a few closed flowers remain on Valencias and grapefruit. Many flowers have passed petal fall. The overall flowering level in this last flowering wave is excellent and the supporting flush in this area looks good. The ‘Citrus Flowering Monitor' has not updated its prediction of two waves of flowers in early and mid March. The computer program clearly does not adjust for cooler weather from the last stages of flower development through bloom. Overall, it appears the second wave was 2 weeks later than predicted, but it appeared to be only one week late around the 15 th of March (predicted bloom date). Reports I have gotten from other areas indicate that their citrus was behaving similarly with a last full bloom dates reported at 3/28 and 3/30 in Ft. Meade and Immokalee, respectively, with large tree to tree variation in full-bloom dates. But was this the second or third wave of flowers to occur this spring?
I did not clearly detect a third wave in the Lake Alfred area and none was mentioned in the Ft. Meade report. In Immokalee, they did see three, but they were able to maintain a prolonged period of drought stress, which may have led to three waves rather than stopping the first two. Further work on drought stress intensity required to stop growth is needed.
Mid-bloom for this season may be about 25 March, which is significantly later than in recent years. The cooler than normal weather is also delaying fruitlet drop. Currently, fruitlet numbers on trees I have looked at are very high. We can expect a heavier than usual May-June drop this year. It should start in June with the late bloom. As of now, trees in good condition look like they will set a good crop. Next week we will talk a little about fruit set prospects on hurricane affected trees.
To view specific spring weather data for a location near you, go to FAWN or to NOAA's 8-day forecast in the Weather Links on this CREC homepage https://crec.ifas.ufl.edu/. Additional weather data links are also listed.

FLOWER BUD INDUCTION ADVISORY #23 for 2004-2005-5/6/05

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS 

The following information has been developed as part of the Decision Information System for Citrus. 
L. Gene Albrigo, Horticulturist 
Citrus Research & Education Center, Lake Alfred, FL

Summary of 2004-05 flowering season with initial evaluation of fruit set potential.

This past winter, flower bud induction appeared to be fairly good with accumulation of 830 to over 1000 hours below 68 degrees F before the first wave of buds initiated growth and from 940 to over 1200 hours before the second wave of buds initiated growth. Initiation of growth dates were also about normal (late December and after the 1st week of January).

In spite of this, the first wave (cohort) of flowers this spring was surprisingly small on mature trees, but the overall flowering level in the second wave of flowers was strong. In the previous 5 or 6 years, the first flowering wave has always been the strongest. Perhaps 2 heavy crops (before hurricane reduction this year) reduced carbohydrate levels to the point that much more induction was need for most buds. Before the second wave of flowering, the supporting spring flush was developing strongly. Because of the cool weather, which delayed the bloom date of the second cohort of flowers, the spring leaf flush was more developed when the second flowering wave occurred. Since the leaves are more developed, they should provide more carbohydrates to the developing fruit thereby minimizing fruitlet drop.

Only the South Florida area around Immokalee and La Belle had dry enough conditions in the winter to alter bloom dates by allowing water stress to develop and prevent early flowering. But the bloom date of the second cohort of flowers in this growing area was not different even though soil moisture records indicated that sufficient drought occurred to prevent early flowering. All regions of the state experienced the weak first wave and delayed but strong second wave of flowering. For the southern area, perhaps the weak first wave plus the late second wave masked any influence of drought stress.

The second flowering wave reached full bloom about 10 days later than the ‘Citrus Flowering Monitor System” predicted. The cool weather during the last stages of flower development apparently stopped development, but the flowering model was not sensitive to this effect. Additional programming will be needed this year to make the last stages of development more responsive to cool temperature delays.

Initial fruitlet numbers on many trees look good. Some fruitlet drop is occurring but the first drop wave has been less than usual because of the cooler than normal weather and good soil moisture. Temperature in both Immokalee and Lake Alfred were usually less than 80 degrees F for highs (only 13 and 7 days in 80s in March, respectively) and April was similarly cool with only 2 days reaching near 90 degrees F in Immokalee. Effective rains have occurred almost every week (6/9 and 7/9 weeks, respectively, with more than 1/3 inch of rain and over half the weeks with an inch or more). Since fewer fruit dropped in the bloom period, we can expect a heavier than usual May-June drop this year. It should start in June, rather than May because of the later major bloom. This is to be expected. There is no reason to panic and think all of the fruit are falling off. As of now, trees generally are in good condition and look like they will set a good crop.

On hurricane affected trees that lost many old leaves, strong fall flushes were stimulated that raised many questions about their ability to flower. Also the losses of buds to flushing that otherwise would have flowered caused concern. Most of the fall flush on hurricane affected trees was able to flower, although post Jeanne flush flowered poorly. As for all trees, temperatures and rainfall have favored fruit set and good spring flush development. Most reports from hurricane affected areas indicate trees are rapidly recovery canopy. Since most trees were not pushed over or lost many limbs, it is likely that most trees, even in zone 1s on the West and East Coasts will have a reasonable recovery crop. Although hurricane affected trees will not be back to normal this year, I expect that they will carry a larger crop than many expected. If not too many orange trees are lost to citrus canker this season (about 6,000 acres so far), we may be able to do as well as in 2002-03 when flowering was very poor. Hurricane tree losses are probably less than 2 %. Grapefruit trees, although they had the most severe leaf losses from the hurricanes, should make considerable recovery this year. Flowering and flush recovery reports are fairly good.

Will fruit be smaller this year? A lighter crop could help fruit size, but the cool spring temperatures do not favor better fruit growth and the later bloom may also minimize fruit size if temperatures stay cooler than normal for much longer. The past two years of heavy crops before the hurricanes and leaf losses in the hurricane paths probably reduced available carbohydrates early in fruit growth, when they are most needed. Overall on mature trees, fruit size could likely be smaller again this year as it was last year.

To view specific spring weather data for a location near you, go to FAWN or to NOAA's 8-day forecast in the Weather Links on this CREC homepage https://crec.ifas.ufl.edu/. Additional weather data links are also listed. This will be the last advisory for this year.

If you want to learn more about regulation of vegetative and reproductive growth of citrus consider the classes offered on Monday nights this coming Fall and Spring Term ( 2005-06), at CREC in Lake Alfred and simultaneously by video conferencing at other University of Florida REC locations in the other citrus production areas and in Gainesville.

FLOWER BUD INDUCTION ADVISORY #1 for 2003-2004-11/6/03

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS 
The following information has been developed as part of the Decision Information System for Citrus. 
L. Gene Albrigo, Horticulturist 
Citrus Research & Education Center, Lake Alfred, FL 

Overview of flower bud induction in Florida –  It is time to start following citrus flower bud induction conditions for the coming year's bloom. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate. A period of 5-12 days of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be slightly warmer than normal, an ENSO Neutral year. If this winter is only slightly warmer than normal, enough hours of low temperatures below 68 degrees F. should accumulate to induce adequate flower buds for a satisfactory crop. Sufficient flower bud induction under Florida conditions should be achieved when total uninterrupted, accumulated hours of low temperatures exceed 850 hours below 68 degrees F. if the current crop is heavy. If the crop load is light, sufficient flower bud induction can occur after 750 hours of accumulated low temperatures. A warm period of 7 to 12 days with max. temperatures > 70 to 75 degrees F. after some low temperatures have accumulated can trigger growth (bud swelling). Fewer days of higher temperatures (> 80 degrees F.) are required to stimulate growth. Current and previous seasons weather information is available on the Florida Automated Weather System fawn.ifas.ufl.edu for locations near you. 

Some flower buds will be induced in the range of 300 to 600 accumulated hrs < 68 degrees F. Warm events after these levels of induction are reached result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods. This scenario results in multiple blooms. When early winter bud break in Florida was not prevented by cool temperatures or drought stress (1963 to 2002 records), multiple blooms occurred in over half of the years. Historically, the time period in which a warm 7-12 day period can lead to some bud growth and then result in multiple blooms is roughly Thanksgiving to Christmas. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is to promote water stress by stopping irrigation before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, mild water stress will have little impact on current crop development or quality. Mild water stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a mild stress condition of citrus trees, buds will not grow in response to high temperatures. If an extended warm period has passed, trees again can be watered to minimize current crop water stress. Although no weather prediction is guaranteed, rains in the winter usually come on the fronts of cool periods. Therefore, the chances of being able to use water stress to prevent an early flower bud differentiation event is reasonably good for most warm periods. A difficulty that occurred 2 years ago, which resulted in a very small crop, was that high temperatures were continuous through the fall until December 18 th . If trees were allowed be water stressed for this extended period, this could lead to low photosynthesis, little fruit growth or sugar accumulation and probably excessive fruit drop.

In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry out by mid-November so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied at low rates as needed until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. This may be risky for ‘Hamlin' or other early maturing cultivars not yet harvested that tend to drop fruit near harvest. Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus'. Future advisories (usually weekly) will update accumulating hours of related temperatures and other weather effects on flower bud induction plus methods for enhancing or reducing flowering intensity as conditions and cultivars dictate. Read the archived advisories from previous years for more background.

 (Figure 1, with added infrmation in color or bold lettering, is from the ‘Flowering Expert System for Florida Citrus'and represents the different aspects of apparent flower induction. The level of potential flowering would be greater (orange line) with a light crop or less (green line) with a heavy crop for the same amount of hours of induction. This system will be tested again this winter with several growers that helped us refin the system last year.)

Last year's results - Last year (2003-2003) by late December we had 850 hours of uninterrupted cool inductive temperatures with a low current crop on the trees. The following warm period initiated almost all the buds on all of the spring and summer flush to differentiate and bloom in early March. We had a fairly leafy bloom of very short duration (slightly more than 2 weeks ). A strong spring flush of leaves may have out competed and suppressed fruit set in navels and grapefruit. In spite of the high temperatures during and following bloom, a good fruit set occurred in other round oranges resulting in the highest crop forecast for Florida that FASS has ever predicted. A good rainfall pattern through the spring and summer allowed the fruit to size better than would be expected for such a large number of fruit. The early March bloom and subsequent warm, wet weather have advanced maturity to result in low juice content (early cultivars are drying out at stem end) with low solids and acidity. Poorer than average fruit quality will make this another difficult year to schedule harvests to get good fresh fruit quality and high yields of solids with moderate ratios for processing.

The new season's situation - In spite of the heavy current crop, most groves had a surprising amount of vegetative flush, particularly spring flush. The strong flush is good for available buds to become flower buds next year. There have to be sufficient buds available to induce in order to have a good crop. Since we have a large current crop, we will need higher accumulations of low temperatures to induce those buds to produce flowers. So far this Fall, little cool weather has occurred to slow down or stop vegetative growth on mature trees, only about 100 to 120 hr < 68 degrees F. in all districts. Also, the National Weather Service (NOAA) predicts that there will be almost no temperatures below < 68 degrees F. during the next 8 days. To view FAWN data for a location near you in the citrus growing areas, use ( www.crec.ifas.ufl.edu ) and click on FAWN or for NOAA's 8 day forecast go to Weather in the homepage graphic locator and 8 day forecast.

The major concern for the next 60 days is the possibility of 1) continuous warm weather that will push vegetative buds to grow as occurred 2 years ago or 2) a warm period with a minimum of 10 to 12 days with max. temperatures > 75 to 80 degrees F following an inductive period of 300 to 500 hrs < 68 degrees F that will initiate differentiation of easily induced flower buds. The first condition will lead to low flowering and the second to multiple blooms. Therefore, keep irrigation amounts low to moderate (if fruit are still present) to minimize growth possibilities, even though a heavy crop should help minimize vegetative growth potential. Keep groves relatively dry and watch for the next advisory.

(Request for potential cooperators) - I believe that we may help our recent problems of low solids and acids for processed oranges and fresh grapefruit by delaying bloom dates each year. This might be accomplished by using water stress to prevent growth during warm winter periods until mid-January has passed. If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin' or ‘Valencia' trees under this protocol.

FLOWER BUD INDUCTION ADVISORY #2 for 2003-2004-11/14/03

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS 
The following information has been developed as part of the Decision Information System for Citrus. 
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL

Other websites for information related to flower bud induction in Florida -The 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt and is linked to http://www.crec.ifas.ufl.edu/crechome/crecweather.shtml . Use (www.crec.ifas.ufl.edu ) and click on FAWN to get up-to-date accumulated low temperatures for a site near you. Look at hrs<65 degrees F for a good idea of accumulated effective temperatures.

The current situation - Finally some cool climate with low temperatures in the flower bud induction range. FAWN records indicate that 100 to 200 hrs < 68 degrees F have accumulate from Ft. Pierce to northern districts, respectively. The 8 day forecast from NOAA indicates that another 80 hours will be accumulated this coming week, bringing our totals to about 200 to 300 hours depending on location. Temperatures are predicted to be lower by the end of next week. Some flower buds will be induced in the range of 300 to 600 accumulated hrs < 68 degrees F. Warm events at these levels of induction result in weak flowering intensity, and therefore many buds remain that can be induced by later cool periods. This scenario results in multiple blooms. Therefore, it will be important to follow the 8 day forecasts closely from this point forward in order to anticipate any warm weather events that could stimulate bud growth.

The only management tool available this early in the season to eliminate or reduce the chance of multiple blooms is to promote water stress by stopping irrigation before these predicted warm periods occur. Now that cool weather has started, mild water stress during warm periods of the typical 7 to 10 day duration will have little impact on current crop development or quality. Mild water stress may be interpreted as leaf wilt observed by 10 or 11 am, but leaves recovering by early the next morning. If no rains interrupt a mild stress condition of citrus trees, buds will not grow in response to high temperatures. If an extended warm period has passed, trees again can be watered to minimize current crop water stress. In the shallow soils of bedded groves, it is relatively easy to create sufficient water stress to suppress growth by withholding irrigation for a few days if no rains occur. In deeper sandy soils, 2 or more weeks without irrigation or rainfall may be required. To minimize the time required for soil to dry sufficiently to initiate water stress, the soil should be allowed to dry down now so that trees show wilt by mid-day. For bedded groves, minimum irrigation at low rates can then be applied more frequently until a weather prediction indicates a warm period is expected. At this time, irrigation should be shut down. For deep sands, the soil needs to be dried out and kept nearly dry below 6 to 8 inches of depth until at least Christmas so that no growth can occur. Minimum irrigations that re-wet perhaps the top 6-8 inches of the root zone may minimize excessive drought, while allowing quick return to a water stress condition if a high temperature period is forecast. In bedded groves, maintaining a fairly high water table (bottom of water furrow) may also be sufficient to minimize the severity of water stress from shutting down irrigation. Therefore, keep irrigation amounts low to moderate (if fruit are still present) to minimize growth possibilities, even though the current heavy crop should help minimize vegetative growth potential. This will allow you to quickly bring about sufficient water stress to stop any bud development should a warm spell be predicted.

Due to a trip next week, a new advisory may not be posted until the Monday, November 24th . Be sure to follow the 8 day forecasts until then.

(Request for potential cooperators) - To improve the situation that may have led to the recent problems of low solids and acids for processed oranges and fresh grapefruit, it may help to delay bloom dates each year. This might be accomplished by using water stress to prevent growth during warm winter periods until at least mid-January has passed. This will delay bloom and then it should delay maturation so that we do not get the rapid decline in acidity and juice content in the Fall. This delay may allow enough time for sugars to accumulate before ratios get too high. If you are interested in putting a block or a few rows of grapefruit or orange trees under this protocol.

FLOWER BUD INDUCTION ADVISORY #3 for 2003-2004-11/22/03

With last weeks weather, we now have 200 to 300 hours of accumulated hours below 68 degrees F. From southern to northern districts, respectively. The next week will be relatively cool according to the NOAA 8 day forecast. This should result in at least another 80 hours of temperatures in the induction range. This should bring all areas to near 300 hours or higher. From that point onward, a warm period is more likely to initiate some bud growth. Any warm periods in the 8 day forecast after this coming week will indicate that it is advisable to stop irrigation to order to induce some water stress. That concern and irrigation procedure should be continued at least until Christmas or New Years.

Remember that with the heavy crop on most trees, it will take higher levels of induction this year to provide good flowering and initiation of differentiation should be delayed until the new year. Until then, keep your eyes on the weather for warm spells.

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom

Current Status:  For those following the accumulated hours on the FAWN site, there are some discrepencies in the data, particularly for the Umitilla site. Rely on the Tavares site for now. Some daily data has negative signs also.

We now have 260 to 400 hours of accumulated hours below 68 degrees F. from southern-coastal to northern districts, respectively. According to the NOAA 8 day forecast, the next week also will be cool . This should result in at least another 84-96 hours of temperatures in the induction range. This should bring all areas to 350 to 500 hours of inductive temperatures. From that point onward, a warm period is more likely to initiate some bud growth.

Any warm periods in the 8 day forecast from now on will indicate that it is advisable to stop irrigation in order to induce some water stress. This procedure to create water stress if a warm spell is indicated in the forecast should be continued at least until Christmas or New Years. It is a good idea to look at the 8-day forecast at least every-other day.

If these cool temperatures continue for two more weeks, some areas may have reached 600 hours of inductive temperatures. That will be the first time to consider using urea or PO3 sprays at the beginning of a warm period to enhance flowering and trigger an early bloom and perhaps obtain earlier maturation. Check last years advisories (below) for general procedures for using flower enhancing sprays.

Remember that with the heavy crop on most trees, it will take higher levels of induction this year to provide good flowering and in general initiation of differentiation should be delayed until the new year or in the 800 or more hour range. Until then, keep your eyes on the weather for predicted warm periods.

FLOWER BUD INDUCTION ADVISORY #5 for 2003-2004-12/8/03

We now have 360 to 460 hours of accumulated hours below 68 degrees F. from southern-coastal to northern districts, respectively. According to the NOAA 8 day forecast, the next week also will be cool with most temperatures below 68 degrees F. This should result in at least another 100 - 140 hours of temperatures in the induction range, although the flowering program only projects an additional 85-83 hrs. This should bring all areas to 500 to 600 hours of inductive temperatures. From December 15 th onward, a warm period is most likely to initiate some bud growth if there is adequate soil moisture for growth.

Any warm periods in the 8 day forecast from now until after New Year's day will indicate that it is advisable to stop irrigation in order to induce some water stress. Irrigation should be minimal (see previous advisories) in order to maintain fruit condition or photosynthesis, but without irrigating the full rooting depth. This will allow rapid creation of water stress if a warm period is forecast and it hasn't rained recently. This procedure to create water stress if a warm period is indicated in the forecast should be continued at least until Christmas or New Years. It is a good idea to look at the 8-day forecast at least every-other day.

If these cool temperatures continue for two more weeks, some areas may have reached 700 to 800 hours of inductive temperatures. That will be the first time to consider using urea or PO 3 sprays at the beginning of a warm period to enhance flowering and trigger an early bloom and perhaps obtain earlier maturation. If you choose to use one of these sprays, urea should be applied at 25 to 28 lbs N per acre in 10-15 (aerial with good spray distributors), 25-30 (ultra low volume), or 50-125 (speed sprayer) gal/ac of water. Speed sprayers can be calibrated for as little as 50 or 60 gal/ac at 4-5 mph if large acreage needs to be covered. High speeds do increase risk of operator driving error. Phosphorous acid should be applied at the equivalent of 2.6 quarts of 26-28 % P product in similar gal/ac as recommended for urea sprays. If you plan to use any of these sprays, be sure you get the product on hand now. If you don't use it for the winter sprays, you can incorporate the products in either bloom or post-bloom sprays.

Remember that with the heavy crop on most trees, it will take higher levels of induction this year to provide good flowering and in general initiation of differentiation should be delayed if possible until the New Year or in the 800 or more hour range. Until then, keep your eyes on the weather for predicted warm periods.

FLOWER BUD INDUCTION ADVISORY #6 for 2003-2004-12/15/03

I have some good news, bad news, good news, bad news, and finally good news for all of you this morning. The first good news is that it rained Sunday to give us good soil moisture levels for maintenance of the current crop essentially everywhere in the citrus growing areas of Florida. The bad news is also that it rained everywhere and the citrus tree buds will start to grow if warm weather occurs in the near future, and we don't have adequate levels of flower bud induction yet considering the heavy current crop. The good news is that cool weather is still projected for the next 8 days. More bad-good news is that Wednesday may bring more rain, but cool weather will probably continue. Also good news, our citrus trees should have reasonable cold hardiness going into the high probability freeze period that lasts until mid-January.
We now have 475 to 680 hours of accumulated hours below 68 degrees F. from southern-coastal to northern districts, respectively. According to the NOAA 8 day forecast, the next week will be cool with almost all temperatures below 68 degrees F. This should result in at least another 130 - 160 hours of temperatures in the induction range, although the flowering program only projects an additional 120 hrs. This should bring all areas to at least 600 to 800 hours of inductive temperatures by December 22 nd . From December 22 nd to January 5 th , a warm period is most likely to initiate some bud growth as adequate soil moisture is available for growth, and it will probably take that long for the trees to use up the available soil moisture so that water stress can occur if a warm period occurs. If we get to January without a warm period and you wish to delay initiation of flowering after the first week of January, irrigation should be minimal, after the current soil moisture is used. This will allow rapid creation of water stress if a warm period is forecast in early to mid-January and it hasn't rained recently. This procedure to create water stress, if a warm period is indicated in the forecast, can be continued until late January. If this procedure can be applied successfully, it should result in a later bloom. Keep watching the 8-day forecasts for indication of a possible warm period and any freeze warnings.
If a warm period occurs before New Year's, all districts should have no more than 700 to 900 accumulated hours below 68 degrees F when buds are initiated to grow. Because of the heavy crop on most trees, it may be advisable to consider using urea or PO 3 sprays just before and at the beginning of such a warm period to enhance flowering. A fairly early bloom is likely to occur under this late December warm period senerio, but the trees will most likely start the flowering process whether you spray or not. It is not a good idea to spray these products during a cold period as forecast for the next 8 days. Very low uptake occurs during cold weather. If you choose to use one of these sprays when temperatures get warmer (daytime highs in the 70s), urea should be applied at 25 to 28 lbs N per acre in 10-15 (aerial with good spray distributors), 25-30 (ultra low volume), or 50-125 (speed sprayer) gal/ac of water. Speed sprayers can be calibrated for as little as 50 or 60 gal/ac at 4-5 mph if large acreage needs to be covered. High speeds do increase risk of operator driving error. Phosphorous acid should be applied at the equivalent of 2.6 quarts of 26-28 % P product in similar gal/ac as recommended for urea sprays. If you plan to use any of these sprays, be sure you have the product on hand. If you stock and don't use these materials for the winter sprays, you can incorporate the products in either bloom or post-bloom sprays.
Until next week, keep your eyes on the weather for predicted warm periods and best wishes with all the Christmas shopping we haven't finished yet.

FLOWER BUD INDUCTION ADVISORY #7 for 2003-2004-12/22/03

This week's advisory has more questions than answers. This is a transition week with the potential for accumulated cool hours to go from moderate to high levels or for trees to start initiation of lower bud differentiation if mid-seventy degree daytime highs continue through the week. Southern areas are particularly in question as to what the trees will decide to do.
We now have 600 to 800 hours of accumulated hours below 68 degrees F. from southern-coastal to northern districts, respectively. According to the NOAA 8 day forecast, the next week again will be cool, but daytime highs will be lower 70 to mid 70 degrees F. This should result in at least another 70 to 80 hours of temperatures in the induction range, the flowering program projects an additional 75-85 hrs. This should bring all areas to at least 700 to 900 hours of inductive temperatures by December 29 th . Any time a warm period occurs now, initiation of differentiation (growth) of many of the available buds is likely as long as adequate soil moisture is available for growth. It will probably take at least another week or 10 days for the trees to use up the available soil moisture so that water stress can occur if a warm period occurs.
Are the next 4 or 5 days the beginning of a warm period that can trigger initiation of flower bud differentiation? Predicted highs of mid 70s for 3 or 4 days may not be enough to trigger growth considering the heavy crop load on most trees. I don't know yet if the warm period will extend long enough to start bud development, but it is possible and may be a reasonable time to boost flowering and probably initiate bud development by spraying urea or PO3. Most locations have too much soil moisture to prevent growth if the warm trend continues. This warming trend may be most critical in southern areas, as temperatures are usually a few degrees higher than the central and northern regions.
If a sufficient warm period does occur before New Year's, all districts should have no more than 750 to 830 accumulated hours below 68 degrees F when buds are initiated to grow. Because of the heavy crop on most trees, it may be advisable to consider using urea or PO 3 sprays just before and at the beginning of such a warm period to enhance flowering in those trees. A fairly early bloom is likely to occur under this late December warm period scenario, but the trees will most likely start the flowering process whether you spray or not if warm temperatures continue. It is not a good idea to spray these products during a cold period but the current forecast indicates that daytime highs will be in the 70s for the next few days. Very low uptake occurs during cold weather. If you choose to use one of these sprays now as temperatures get warmer (daytime highs in the 70s), I would wait until the possible rain front predicted for Tuesday night-Wednesday goes through. Then urea should be applied at 25 to 28 lbs N per acre in 10-15 (aerial with good spray distributors), 25-30 (ultra low volume), or 50-125 (speed sprayer) gal/ac of water. Speed sprayers can be calibrated for as little as 50 or 60 gal/ac at 4-5 mph if large acreage needs to be covered. High speeds do increase risk of operator driving error. Alternatively, phosphorous acid (PO3) should be applied at the equivalent of 2.6 quarts of 26-28 % P product in similar gal/ac as recommended for urea sprays. If you plan to use either of these sprays, you should have the product on hand by now. You can incorporate the products in either bloom or post-bloom sprays if you don't use it now.
We have now reached the stage where navel trees with a light crop, most navel trees this year, are likely to have excessive flowers induced. These flowers will be weak and face excessive competition from one another. One way to minimize this effect is to apply a gibberellin spray when a warm spell occurs (EDIS - Enhancing Cropping of Low-Yielding, Heavily Flowering Citrus by Reducing Floral Initiation Ed Stover and Gene Albrigo; EDIS publ. # HP 799). If this period of warm temperatures looks like it will continue through the week, allow 3 or 4 days of the warm spell to occur before spraying to moderate the effect. A spray of 20 oz. GA per acre is recommended in at least 100 to 125 gal / acre.
Alternative (IF) scenario : If this week's warm weather is not sufficient (stops by Christmas day), we can get into January without initiation of flower bud differentiation. If we don't have much rain on Tuesday-Wednesday, we can re-impose water stress for an early January warm period by withholding irrigation. This procedure to create water stress, if and when another warm period is indicated in the forecast, can be continued until late January. If this procedure can be applied successfully, it should result in a later bloom. Keep watching the 8-day forecasts for indication of a continuation of the predicted warm period, a possible downturn in temperatures and anything else you might wish to hope for on Christmas.

FLOWER BUD INDUCTION ADVISORY #8 for 2003-2004-12/29/03

We now have 750 to 830 accumulated hours below 68 degrees F. from southern-coastal to northern districts, respectively. According to the NOAA 8 day forecast, the next week will have highs in the upper 70s to 80 degrees F. This should result in 85 hours of temperatures in the induction range, and should bring all areas to 830 to 1000 hours of inductive temperatures by January 4th. This induction level should be high enough to result in a reasonable level of flowering, particularly if urea or PO3 is sprayed during the current moderate warm period.
It appears to me that the continued highs of near 80, especially in the southern region, may be sufficient to initiate differentiation (growth) of many of the available buds if soil moisture has not been depleted to the point that afternoon wilt occurs. If soil moisture does appear to be in the wilt range, continuing without irrigation or deficit irrigation should delay initiation of flower development. This procedure to maintain water stress can be continued until mid January by applying minimal irrigation. Keep watching the 8-day forecasts for indication of the continuation of this moderate warm period or cooler weather that will allow moderate irrigation.
However, if no signs of water stress are evident or you have continued to irrigate, then bud development is likely to start within a week if these moderately warm temperatures continue. Because of the heavy crop on most trees, it is advisable to consider using urea or PO 3 sprays over the next 7 to 10 days. A fairly early bloom is likely to occur under this late December warm period, but the trees will most likely start the flowering process whether you spray or not if soil moisture is adequate for growth. Reasonable uptake of these spray products should occur based on the temperatures forecast for the next 8 days. If you choose to use one of these sprays, urea should be applied at 25 to 28 lbs N per acre in 10-15 (aerial with good spray distributors), 25-30 (ultra low volume), or 50-125 (speed sprayer) gal/ac of water. Speed sprayers can be calibrated for as little as 50 or 60 gal/ac at 4-5 mph if large acreage needs to be covered. High speeds do increase risk of operator driving error. Phosphorous acid should be applied at the equivalent of 2.6 quarts of 26-28 % P product in similar gal/ac as recommended for urea sprays.
Navel trees with a light crop, most navel trees, are now likely to have excessive flowers induced. These flowers will be weak and face excessive competition from one another. One way to minimize this effect is to apply a gibberellin spray once the next warm spell occurs ( EDIS - Enhancing Cropping of Low-Yielding, Heavily Flowering Citrus by Reducing Floral Initiation Ed Stover and Gene Albrigo; EDIS publ. # HP 799). Allow 3 or 4 more days of this warm period to occur before spraying to moderate the effect. A spray of 20 oz. GA per acre is recommended in 125 to 150 gal / acre.
If I receive an update on soil moisture situation in South Florida, I will post an advisory update tomorrow or the next day as to whether trees are more likely or less likely to initiate flower bud growth in the next week. Watch the weather! I hope you had a Merry Christmas and best of luck with a Happy New Year.

FLOWER BUD INDUCTION ADVISORY #10 for 2003-2004-1/12/04

We now have 980 to 1200 accumulated hours below 68 degrees F. from southern-coastal to northern districts, respectively. According to the NOAA 8 day forecast, the weather next week will provide 70 to 120 more hours of inductive temperatures with warm days (mid 70s) starting Thursday to Saturday from southern to northern districts, respectively. This should result in all areas being over 1000 hours of inductive temperatures by January 18th.
The flowering model indicates that trees in all areas have started differentiation of flower buds for the first wave of flowers this coming Spring. Initiation dates for flower bud differentiation were December 22-23 for most districts and December 29 th for the Indian River District. These initiations of growth started after 780 to 880 hours of inductive temperatures. Bloom dates for this wave of flowers are now predicted to be March 3 to 6, with Ft. Pierce being the later date. We have now checked buds on some well watered navel and Valencia trees at Ft. Pierce and a few first and second leaf axis buds are swelling or even have a leaf tip showing, but fewer than reported last week at Lake Alfred.
Since induction hours were in the 800 range, this should be a major bloom with any secondary bloom of smaller magnitude, but due to the heavy current crop the next bloom wave could still contain a fairly large number of flowers. With the projected additional hours below 68 degrees F. this week, about 320 to 440 hours will be added to induction for the second bloom wave. This should put most trees into an acceptable induction range for total flowers, even though they may come in two waves. According to the flowering model, some districts already have a second initiation of differentiation with a predicted bloom date of March 13. If correct, this flowering wave should be small and appear as part of the first wave since they are only 10 days apart.
If soil moisture was maintained in the deficit range during the late December warm period, trees may have only one flowering event triggered during the next warm period, if soil moisture is adequate at that time. A later date of initiation may be obtained if soil moisture was low during the late December warm period, and a low to deficit soil moisture condition is maintained until late January. The only FAWN station in the citrus area reporting any significant rain this past week was Lake Alfred with 0.34 inches (January 9-10). Trees in this area may use sufficient soil moisture to return soils to a deficit condition before another prolonged warm period occurs. Unfortunately, many of us put a shallow irrigation on early last week so that after the rain more of the root zone is wet in the Central Florida area than desirable for deficit irrigation management.
If some blocks have a very heavy crop and you were not able to get to a soil moisture deficit condition (no wilt by noon during last warm period), a flower enhancing spray of urea or PO 3 may be beneficial at the end of the current cool period to boost the second wave of flower initiation. Look with a hand lens at the first two buds at the terminal ends of 10 to 15 spring and summer shoots to see if some of them are swollen. If some are swollen, you did not stop initiation with any attempt at deficit irrigation. If you choose to use one of these sprays, urea should be applied at 25 to 28 lbs N per acre in 10-15 (aerial with good spray distributors), 25-30 (ultra low volume), or 50-125 (speed sprayer) gal/ac of water. Speed sprayers can be calibrated for as little as 50 or 60 gal/ac at 4-5 mph if large acreage needs to be covered. High speeds do increase risk of operator driving error. Phosphorous acid should be applied at the equivalent of 2.6 quarts of 26-28 % P product in similar gal/ac as recommended for urea sprays. Remember that temperatures should be in the low 70s or higher on days you spray to get good uptake.
Navel trees with a light crop, most navel trees this year, are now likely to have excessive flowers induced and 2 waves of flowers in the Spring. These flowers will be weak and face excessive competition from one another, plus an increased potential for post-bloom fruit drop due to multiple blooms, if Spring rains occur. One way to minimize this effect is to apply a gibberellin (GA) spray towards the end of this warm period ( EDIS - Enhancing Cropping of Low-Yielding, Heavily Flowering Citrus by Reducing Floral Initiation Ed Stover and Gene Albrigo; EDIS publ. # HP 799). A spray of 20 oz. GA per acre in 125 to 150 gal / acre can be applied for decreasing flowering of navels, other seedless cultivars and poorly setting Rhode Red strains. If you did not spray a block already, some benefit will likely come from spraying when temperatures reach the mid 70s later this week. This should block any new induction that has occurred and perhaps still diminish the number of flowers in the first wave of flower induction now projected to reach full bloom in early March.

FLOWER BUD INDUCTION ADVISORY #11 for 2003-2004-1/19/04

We now have 1100 to 1330 accumulated hours below 68 degrees F. from southern-coastal to northern districts, respectively. According to the NOAA 8 day forecast, the weather next week will provide 130 more hours of inductive temperatures with daytime highs of 63 to 70 starting tomorrow, Tuesday, and continuing until Saturday. The warmer temperatures will be in southern areas but still only slightly higher than the 68 degree F. threshold for flower bud induction. This should result in all areas being over 1220 hours of inductive temperatures by January 24 th , when a warm period may occur since daytime highs are predicted to be 72 to 76 degrees F. for all areas on the weekend. If that warm trend this weekend continues for another 3 or 4 days next week, all potential flower buds will probably initiate growth if they have not already done so.
The flowering model indicates that trees in all areas have started differentiation of flower buds for two waves of flowers this coming Spring. Initiation dates for the first wave of flower bud differentiation were December 22-23 for most districts and December 29 th for the Indian River District. This growth started after 760 to 840 hours of inductive temperatures. Bloom dates for this wave of flowers are now predicted to be March 1 to 5, with Ft. Pierce being the latest date. As stated last week, the first wave of initiation has been confirmed by detecting swollen buds. A second wave of flower bud initiation also started in all districts January 2 to 9 th for northern to southern districts, respectively. These events occurred when accumulated inductive hours were 1000 to 915 hours from north to south and the projected bloom dates are March 12 th to 18 th from north to south.
Since induction hours were in the 900 plus range by the second initiation, a majority of potential flower buds should now be induced and growing. With the additional hours below 68 degrees F. expected be 320 to 470 hours by this coming weekend, a third initiation should account for all potential flower buds. This should put all trees into an acceptable induction range for total flowers, even though they may come in a prolonged bloom.
Some growers may have successfully managed to maintain soil moisture at a low level until this weekend and will see one heavy and concise bloom from one major initiation of differentiation after this current cool period. All areas report 0.7 to 1.8 inches of rain on Sunday, January 18 th , and more rain is expected today. With the projected warm period starting next Saturday, all remaining buds that can be initiated to develop as flower buds should be. I guess the bloom date for this wave will be about March 24 th . The Citrus Flowering Monitor System should predict a more accurate date of bloom later next week if the warm period continues until mid-week.
If no urea or PO3 spray was applied earlier, it is very doubtful that any benefit will come from its application now that accumulated low temperature induction levels are so high. It would be better to save any left over material for a bloom or post bloom spray.
Navel trees will have excessive flowers induced and at least 2 waves of flowers in the Spring if low soil moisture levels were not obtained during earlier warm periods. These flowers will be weak and face excessive competition from one another, plus an increased potential for post-bloom fruit drop due to multiple blooms, if Spring rains occur. If you have not done so yet, one way to minimize this effect is to apply a gibberellin (GA) spray towards the end of this coming warm period ( EDIS - Enhancing Cropping of Low-Yielding, Heavily Flowering Citrus by Reducing Floral Initiation Ed Stover and Gene Albrigo; EDIS publ. # HP 799). A spray of 20 oz. GA per acre in 125 to 150 gal / acre can be applied for decreasing flowering of navels, other seedless cultivars and poorly setting Rhode Red strains. Spray later next week if temperatures continue to be in the low to mid 70s or higher. This should block any new induction that has occurred since the last warm period earlier in January and perhaps still diminish the number of flowers in the second wave of flower induction now projected to reach full bloom in mid-March.
Watch the weather and the flower buds as they both develop.

FLOWER BUD INDUCTION ADVISORY #12 for 2003-2004-1/26/04

We now have over 1250-1450 accumulated hours below 68 degrees F. from southern-coastal to northern districts, respectively. According to the NOAA 8 day forecast, the weather this week will provide 100 more hours of inductive temperatures with daytime highs of 80 to 73 today and tomorrow followed by 2 to 3 cool days and then back in the mid-70s for the rest of the week. This should put all areas above 1300 hours as the last potential wave of flower buds is initiated to differentiate, if any potential flower buds still remain uninitiated.
The flowering model indicates that trees in all areas have started differentiation of flower buds for two waves of flowers this coming Spring. For the Immokalee area, three initiation dates are indicated with bloom dates of March 2, 13 and 22 for the three waves. In other areas from coastal southern to northern, bloom dates for the first wave of flowers are now predicted to be March 5 to 1. The second initiation wave of flower bud differentiation has projected bloom dates of March 18 th to 12 th from south to north.
Since induction hours are now in excess of 1250 hours and warm temperatures are happening and expected to continue most of this week, we can expect that all potential flower buds are probably going to initiate growth this week. If all 3 waves occur, then we will have a prolonged bloom period through most of March. If you successfully created water stress from late December to mid-January, then you should get a peak bloom date of 22 to 25 March according to the model. We can expect a fair bloom on trees that produced a reasonable amount of new Spring and Summer flush last year. We will assess the impact of the heavy current crop on flowering and fruit set in a later advisory.
If no urea or PO3 spray was applied earlier, it is very doubtful that any benefit will come from its application now that accumulated low temperature induction levels are so high. It would be better to save any left over material for a bloom or post bloom spray. We will test this timing to see if it is correct that little benefit will come from an application this late in the flower bud induction-initiation of differentiation process.
Navel trees will have excessive flowers induced and at least 2 waves of flowers in the Spring if low soil moisture levels were not obtained during earlier warm periods. These flowers will be weak and face excessive competition from one another, plus an increased potential for post-bloom fruit drop due to multiple blooms, if Spring rains occur. If you have not done so yet, one way to minimize this effect is to apply a gibberellin (GA) spray this week while temperatures are warm enough to get good uptake (low to mid 70s or higher so avoid Tuesday or Wednesday this week) ( EDIS - Enhancing Cropping of Low-Yielding, Heavily Flowering Citrus by Reducing Floral Initiation Ed Stover and Gene Albrigo; EDIS publ. # HP 799). A spray of 20 oz. GA per acre in 125 to 150 gal / acre can be applied for decreasing flowering of navels, other seedless cultivars and poorly setting Rhode Red strains. This should block any new induction that has occurred since the last warm period earlier in January and perhaps still diminish the number of flowers in the second wave of flower induction now projected to reach full bloom in mid-March.

FLOWER BUD INDUCTION ADVISORY #13 for 2003-2004-2/2/04

We now have 1250 to 1600 accumulated hours below 68 degrees F. from southern-coastal to northern districts, respectively. According to the NOAA 8 day forecast, the next 5 days will be at least in the mid to high 70s and probably the low 80s in southern areas. Next weekend may be in the high 60s, but final initiation should have begun before then. All inducible buds have been induced, and all initiation of flower bud differentiation should have occurred by next weekend if there is available soil moisture.
The flowering model indicates that trees in all areas will now have 3 waves of initiation after this warm spell, if flower buds were still available. Predicted bloom dates have moved back a little because of cool weather with full bloom dates now of March 2-5, 13-18 and 21-27 for the 3 waves of initiation. Central and northern areas may have some bloom about April 1 st from the 3rd wave of initiation.
Since induction hours were in the 900 plus range by the second initiation, a majority of potential flower buds should now be induced and growing. With the additional hours below 68 degrees F. since then in the 400 to 500 hour range, the third initiation should account for all potential flower buds. This should put all trees into an acceptable induction range for total flowers, even though they may come in a prolonged bloom through most of March for well-watered trees.
If your blocks did not receive rainfall this past week, irrigation should be started this week to promote initiation during this warm spell to promote end of March bloom or development of already induced flower buds. Irrigation rates should be dictated by the weather but amounts applied don't need to be particularly high until new flush is pushing, when tree water use will increase greatly. If you followed the low irrigation protocol successfully, this warm week should result in a major bloom at the end of March if you irrigate now or had sufficient rainfall this past week.
Next week we should have a more exact 3 rd wave predicted bloom date for northern areas, an update on changes in predicted bloom dates for all areas after a week of warm weather, and a guess about the interaction of flowering intensity with last years crop load to determine potential for our next crop.
Time to fertilize, if you haven't yet, and watch those flower buds develop.

FLOWER BUD INDUCTION ADVISORY #14 for 2003-2004-2/9/04

We now have over 1600 accumulated hours below 68 degrees F. for all districts, but final initiation of flower bud differentiation started at about 1000 to 1200 hours from northern to southern districts, respectively. According to the flowering model,. central and northern areas have only 2 flowering waves initiated, while southern areas have 3. With the heavy current crop that most trees bore this year, there may have been buds left for a third wave in some blocks in the central and northern areas. We will have to see if that happens and adjust the flowering model if it does.
Bloom dates for Valencias are March 1-3, March 12-16 and March 21-24 (southern areas only). If a third wave occurs in central and northern area, it appears that the full bloom date would be about April 1 st . Hamlins may be a little behind these dates and grapefruit also. The first flowering will be in navels and Ambersweet (Feb. 22-26 and March 5-7), probably without a third wave. Mandarins will be last and the model predicts bloom dates of March 8-11, March 19-22 and March 28-30. Try to have bees placed by late February and if possible move the hives to mandarin blocks after the first week of March. In any case, place the hives so the bees will have to go through the mandarins to reach other cultivars.
If you successfully water stressed your trees during the first and second winter warm periods, you should observe only one or two of the later flowering dates. Please email me bloom date observations and describe attempts to impose water stress albrigo@crec.ifas.ufl.edu.
Where do we stand on crop potential for the coming year? We have reasonable levels of flower bud induction, but not quite as good as last year for the first wave. The second wave will be in response to a higher level of total induction than last year, since last year essentially all the flowers came in the first wave. The current heavy crop, whether harvested or not, will suppress flowering levels and there are fewer spring and summer shoots to have flowers for the new crop. Historically, yield swings that appear to be from alternate bearing effects have been about .4 to .7 boxes per mature tree equivalent, with Hamlins having less response. Previously, the crop load interaction with level of flower induction was never evaluated. We could imagine that this should be a fairly strong alternate bearing year, but it is coupled with a good year for flower bud induction and the vegetative flush in most groves was better than expected for the strong bloom and set. Well if you can weight all of those factors correctly, you have a good idea of what are crop potential is going into the bloom at the end of this month.
I will be gone for two weeks, so you will not be able to find out what I think the balance is. I will answer emails about flowering dates and induction levels for water stressed blocks. The next advisory will be in two weeks (mid-week, maybe February 25)

FLOWER BUD INDUCTION ADVISORY #15 for 2003-2004-2/23/04

I just returned from the 10th International Society of Citriculture Congress in Agadir, Morocco. I only have had time to look at flower development in our teaching block at Lake Alfred. Flower development looks like it is nearly on track with the flowering model. Navels in this area should be in full bloom tomorrow. Our trees look like they will make that within a day or two at worst (see pictures at the end of this advisory). Other oranges and grapefruit are projected for the first of March (again see picture taken today). Mandarins may meet the March 7 projection.
For our trees, it looks like most of the navel bloom will come in the first wave, while other orange cultivars appear to have a 50-50 split between the first and second wave. Today, the second wave flowers in Valencia or Hamlin trees are small pinheads to medium pinheads. In general, these trees have a good bloom coming with one or two flowers per inflorescence with several leaves. This bodes well for a good set if spring weather is reasonably good.
I have not had time to visit any blocks were winter irrigation was reduced to delay bloom. By next Monday, I hope to have some information from our test blocks and cooperator blocks. I expect that if bloom was delayed until late March, the new buds will be in early bud-break now.
Please email your observations of full bloom dates for different waves and your evaluation of proportion of flowers in each wave. For well watered trees, I don't think there will be many buds available for a third wave, unless some of the smallest pinheads take until late March to develop.

FLOWER BUD INDUCTION ADVISORY #16 for 2003-2004-3/1/04

Flower development appears to be about 1 week later than the flowering model predicted in Lake Alfred. Navels in this area should have been in full bloom on Feb. 24 th according to the model, but bloom appears to be closer to March 2 nd , while Valencias were targeted for this past weekend, but they are a few days off in a couple of blocks examined near Lake Alfred. Southern areas were projected for Feb. 20-22 for navel bloom and Feb. 26 to 27 for Valencia bloom. Northern areas were supposed to have the first wave of navel flowers bloom on Feb. 26 to 28 and Valencias on March 2-5. Second wave flowers should be open about 10 days later. Please report your observations of full bloom dates in your district ( albrigo@crec.ifas.ufl.edu ).
The delay in bloom may be partially due to cooler weather this past week stopping or slowing flower development, but the model accuracy is plus or minus 5 days. Corrections in the model are needed if the model consistently under or over predicts bloom date. Even with a one week delay from the model, bloom again this year is early and most flowers should be past petal fall before 15 March.
It is easy to see two waves of flowers developing on the trees, but inflorescences are at various stages so that there will be flowers open over an extended period, at least in this area. For well watered trees, I don't think there will be many buds available for a third wave, unless some of the smallest pinheads take until late March to develop. A third wave was projected for the southern citrus areas. In this part of Central Florida, it is not easy to see evidence of a third wave that would be flowering in late March. We did clearly delay flowering in one block of Hamlin and Flame trees by reducing winter irrigation. I don't know yet how much later full bloom dates will be for these two cultivars in this winter droughted block.

FLOWER BUD INDUCTION ADVISORY #17 for 2003-2004-3/8/04

Flower development: Flower development still appears to be about 1 week later than the flowering model predicted in Lake Alfred. Hamlin and Valencia trees are near full bloom for the first wave of flower buds. For second wave flowers, tree to tree and grove to grove variation is evident, with some trees having a significant amount of second bloom and some with almost none. On Valencia trees, second wave flower buds with pinhead flowers are more likely to be on branches near large clusters of fruit. Photos 1 and 2 show the delay of flowering on a Hamlin tree that has not been harvested compared to one that was harvest 1 month ago. Yesterday, I observed several blocks in the Ft. Pierce area in full bloom.
The delay in bloom may be partially due to cooler weather 2 weeks ago slowing flower development. The model accuracy is plus or minus 5 days and we may be experiencing one of the larger variations, but last year full bloom was initially predicted for 6 to 7 March and then the model shifted to predicted bloom date to 1 March for this area. The actual date ended up about 7 March. Therefore, I can't say if the bloom model prediction was late or not last year, but its mid-course change was not correct. The model's response last year and this year to temperature (underestimating bloom date) does suggest that the model may be advancing flower development too rapidly. We may need to adjust the model's response to temperature to estimate a later bloom date. Next year, we will run an adjustment based on the last two years and compare it to the current equation to see if a new equation fits the observed bloom dates better.
In most cases that I have observed, the second wave of flowers is smaller than the first wave and represents perhaps not more than 10 to 20 % of the total flowers. If flowers are at different stages in the same inflorescence, they are still all from the same wave of flowering. If all of the flowers in an inflorescence are still at some stage of pinhead or small but only a little white showing, that is a different wave of flower buds from those that currently have flowers at full bloom to popcorn in the inflorescences (photo 3, left side vs right side).
We did delay flowering in one block of Flame trees by reducing winter irrigation, but bloom on Hamlin trees in this same block appear only slightly delayed from two nearby irrigated blocks. I don't know yet how much later full bloom dates will be for these two cultivars in this winter drought stressed block compared to well irrigated trees, but it does not appear that the delay will be more than 7 to 10 days.
Please email your observations of full bloom dates for different waves, and your evaluation of proportion of the total flowers in each wave. How far off from your observations were the predicted bloom dates for your area (see advisory 16)?

FLOWER BUD INDUCTION ADVISORY #18 for 2003-2004-3/15/04

Flower development: Full bloom is on the downside in Lake Alfred for Hamlin and Valencia trees, but more flowers are open today than last Monday. All you have to do is smell the air to know that. For second wave flowers, tree to tree and grove to grove variation is evident, with individual flowers ranging from pea size down to 1/8 th inch diameter. I saw only one later bloom wave inflorescence on 10 trees. Grapefruit with current crop not harvested are a little behind Valencias with crop. Mandarins have some open flowers, maybe 5 %, with Murcotts the least developed.
The general effect of climate and genetics in this area is to have produced a prolonged bloom that will probably last another 7 to10 days before the majority of flowers are past petal fall. Many of the inflorescences are generative with nothing but old leaves on last year's shoots. Tree to tree and within tree variability has occurred. On our trees, spring flush looks light.
The delayed bloom in one block of Flame trees with reduced winter irrigation is not to full bloom. Very few flowers are open. On the other hand, the same treatment in the Hamlin trees has delayed bloom no more than 3 or 4 days when compared to 2 nearby irrigated blocks. The delay in the grapefruit still appears to be at least 7 to 10 days.
I expect that 2 more advisories will be posted this year to wrap up the bloom period and have a perspective of temperatures during the first period of fruit set. I would like to report some grower observations of bloom in your areas, but I have to have reports to do that. All information will be kept anonymous. Please report your observations of full bloom dates in your district ( albrigo@crec.ifas.ufl.edu ). How far off from your observations were the predicted bloom dates for your area (see advisory 16)?

FLOWER BUD INDUCTION ADVISORY #19 for 2003-2004-4/5/04

Final advisory of 2003-04 flowering season
Flower development: Full bloom dates were about 5 to 7 days later than predicted by the flowering monitor in many groves around the state. However, some growers indicated that the predicted dates did reflect what they observed, and they clearly saw at least 2 waves of flowers as predicted.
Flowering intensity reports and observations were from light to heavy. Most growers reported good bloom and a few thought there were more flowers than last year. Some blocks did have light flowering. We expected fewer flowers than a year ago because of the current heavy crop and the slightly lower induction level than a year ago. In general, I would say that flowering was better than expected considering the heavy crop on most trees. The spring flush was also good considering the crop and the level of flowering. This should help to reduce the May-June drop.
The flowering period was extended considerably, partially due to 2 waves of flowering that significantly overlapped, but perhaps equally because of cool temperatures that have lasted until today. Few days exceeded the low 80s.
Fruit set perspective: The cool weather during the first drop period (bloom + 3 weeks) minimized any heat or water stress related drop. We will probably have an apparent heavy May-June drop because of this. This will not necessarily indicate a poor fruit set year. May-June is usually hot and dry, and we still get large crops in spite of this (consider last year).
An important factor in the final set of Valencias is the heavy current crop that will likely stay on more trees than usual through much of the May-June drop period while waiting for processing. This will increase the May-June drop and be a larger contributing factor to the level of alternate bearing in Valencia than will the return flowering level.
Fruit size: The new crop is starting growth under lower temperatures than the previous 2 or 3 years. This should result in a slow start on fruit growth and translate into smaller fruit than in the previous two years as far as growth temperatures are concerned. Above average rainfall in the spring and autumn can help offset the lower than normal early spring temperature effect on fruit growth.
Summary: Above you have my assessment, with some help from grower cooperators, of flowering, fruit set and fruit size for this coming crop,. Put it all together and you too can speculate on an early estimate of what the new crop will be. My first estimate for the year is in the vault at Price-Waterhouse. Good luck and good prices would be nice. See you next year. ( albrigo@crec.ifas.ufl.edu ).

FLOWER BUD INDUCTION ADVISORY #1 for 2002-2003-11/11/02

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS 
The following information has been developed as part of the Decision Information System for Citrus. 
L. Gene Albrigo, Horticulturist 
Citrus Research & Education Center, Lake Alfred, FL 

This is a service to our citrus growers posted on the CREC website. The indicated Expert System on intensity and time of bloom can be accessed at the designated Web Site: http://disc.ifas.ufl.edu/bloom
If you are not familiar with the website and flower bud induction in citrus you should read the overview section below the current status paragraph.

It is the time of year to start following citrus flower bud induction conditions for the coming year's bloom. Cool weather stops growth and then promotes induction of flower buds as more cool weather accumulates. A warm spell can then initiate differentiation which after sufficient days of warm temperatures leads to bloom. The meteorologists say that this winter in Florida will be slightly cooler than normal, a weak El Nino year. Potentially, sufficient cool temperatures should accumulate, below 68 degrees F, to induce adequate flower buds for a good crop yield. Sufficient flower bud induction under Florida conditions is achieved when 850 to 1000 hours of accumulated cool temperatures < 68 degrees F occurs without interruption before a warm spell ( ie., 7 to 12 days with max. temperatures > 80 and min. temperatures >70 degrees F) triggers the beginning of bud growth. So far this year little cool weather has occurred to slow down or stop vegetative growth on mature trees, 150 to 175 hr < 68 degrees F in southern districts and 250 to 275 hr < 68 degree F in northern districts. This information is available on the Florida Automated Weather System as less than 65 and less than 70 degrees F (www.fawn.ifas.ufl.edu). A third cool spell of the Fall is predicted to start Wednesday or Thursday and continue for the following 5 or more days depending on location in the citrus growing areas ((www.crec.ifas.ufl.edu ), click on Research and Extension, then weather and 8 day forecast). The 8 day forecast from the National Weather Service predicts that our accumulated cool weather (below 68 degrees F) will be 275 to 320 hours in northern locations and 200 to 250 hours in southern locations 8 days from now.

The major concern for the next 60 days is the possibility of an early warm spell that will initiate differentiation of easily induced flower buds or push vegetative buds to grow. Some flower buds will be induced in the range of 300 to 600 accumulated hr < 68 degrees F. Warm events when only these levels of induction have occurred result in initiation of a weak flowering event, and therefore, many buds remain that can be induced by later cool spells resulting in multiple blooms occurring. When early winter bud break was not prevented in Florida (1963 to 2002 records), multiple blooms occurred in over half of the years. The time period in which a warm spell can lead to some bud growth and then result in multiple blooms is roughly Thanksgiving to Christmas. Extreme warm conditions existed last Fall and early Winter and resulted in the poor flowering and the low crop being experienced this year. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is to allow water stress to occur during these warm periods. The difficulty last year was that warm weather was continuous until December 18th. Allowing trees to be in water stress for this extended a period could lead to poor photosynthesis, little fruit growth or sugar accumulation and excessive fruit drop of the current crop, particularly for early maturing cultivars. If the warm spell(s) are of the more typical 7 to 10 day duration, mild water stress will have little impact on overall fruit development or quality. Mild water stress may be interpreted as leaf wilt observed by 10 or 11 am.

With the shallow root systems in bedded groves, it is relatively easy to reach sufficient stress to suppress growth by withholding irrigation for a few days. In deeper sandy soils, 2 or more weeks may be required for a fully saturated root zone to dry sufficiently for leaf water stress symptoms to appear. To minimize the time to initiate water stress, the soil should be allowed to dry out in late fall so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied as needed until a weather prediction indicates a warm spell is expected. At this time irrigation should be shut down. For deep sands, the soil needs to be dried out to wilt and then leave part of the lower root zone dry each irrigation until at least Christmas so that no growth can occur. This may be risky for Hamlin or other early maturing cultivars that tend to drop fruit near harvest.

If no rains interrupt a mild water stress condition of the citrus tree, buds will not grow in response to warm temperatures. Once a warm spell occurs and has passed with the trees under water stress, trees again can be watered to minimize fruit water stress. Although no weather prediction is guaranteed even by the meteorologist, rains in the winter usually come on the fronts of cool spells. Therefore, the chances of being able to apply water stress to prevent an early flower bud differentiation is reasonably good for most short duration warm spells. Each of this year's three cool spells, including the current predicted one, has had a rain prediction on the front of the cool spell.

The next few advisories will update accumulating weather effects on flower bud induction and provide timing information if water stress should be applied. As we reach appropriate moderate levels of flower bud induction, information concerning methods for enhancing or reducing flowering intensity (sprays of urea to enhance or GA3 to reduce) will be provided (see last years advisories for more information about these sprays). Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus'. Our new flowering decision support system (expert system) that is now in test with some growers will be discussed during two talks scheduled in the next two months. Factors controlling flowering, use of control strategies for stopping early flowering events, enhancing or diminishing flowering intensity and when to use these options will also be discussed. These two talks are November 12th at 11 am in the CREC Ben Hill Griffin Hall and on December 17th at 10 am in the La Belle, Collier County Extension Office Auditorium.

FLOWER BUD INDUCTION ADVISORY #2 for 2002-2003-11/18/02

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS 
The following information has been developed as part of the Decision Information System for Citrus. 
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

This is an update from the first advisory. Essentially all areas received heavy rains that saturated the root zone. However, a full week of cool temperatures are expected through next Monday, and therefore no bud growth will occur. Growers should follow the NOAA 8 day forecast (http://www.crec.ifas.ufl.edu/CRECHOME/crecweather.shtml) later in the week to see if a warm spell is predicted for next week. If so, sufficient cool temperatures will have accumulated that a weak initiation of flowering could start with the first significant warm spell. With a weak induction level, some apex buds may start to differentiate if sufficient soil moisture is present. Growers should allow trees to reach late morning wilt before starting to irrigate again. See last weeks advisory for general guidelines for irrigation depending on rooting depth after the current soil moisture is used by the trees.

Southern areas have accumulated about 200 hours below 68 degrees F and should reach the 300 mark by next Monday. Northern areas are at about 250 hours and should exceed 300 hours by next Monday.

Remember that the goal is to get to Christmas and/or above 900 hours below 68 degrees F before allowing initiation of flower bud differentiation. At that time flower bud enhancing sprays such as urea and increasing irrigation rate are appropriate. I will discuss those options in one or two weeks after we reach 600 hours below 68 degrees F.

Applying water stress for any warm spells that may occur before we reach those accumulated cool temperature goals, should minimize any early bud development and may also conserve freeze hardiness that the trees may have gained. At the same time, short periods of water stress (7 to 10 days) will have little adverse effects on fruit size or fruit droppage.

This is a further update on Florida weather conditions as they influence citrus flower bud induction. Most of the soil moisture in the root-zone from last week's heavy rains should now be dissipated. But irrigation should be used sparingly so that drought can be initiated by stopping irrigation if a warm spell occurs before Christmas. Another full week of cool temperatures is expected through next Monday, and therefore no potential for bud growth should occur this week. Growers should follow the NOAA 8 day forecast (http://www.crec.ifas.ufl.edu/CRECHOME/crecweather.shtml) later in the week to see if a warm spell is predicted for next week. If so, sufficient cool temperatures will have accumulated that a weak to low initiation of flowering could start with the first significant warm spell. With a low induction level, many apex buds may start to differentiate if sufficient soil moisture is present. Growers on deep sands should allow trees to reach mid-day wilt before starting to irrigate again. Trees in bedded groves should show wilt symptoms more quickly than those on deep sands. See the initial advisory for general guidelines for irrigation depending on rooting depth after the current soil moisture is used by the trees.

Southern areas have accumulated about 300 hours below 68 degrees F and should be above the 400 mark by next Monday. Northern areas are at about 350-400 hours and should exceed 450-500 hours by next Monday.

Remember that the goal is to get to Christmas and/or above 900 hours below 68 degrees F before allowing initiation of flower bud differentiation. At that time flower bud enhancing sprays such as urea and increasing irrigation rate are appropriate. I will discuss those options next week as we approach accumulation of 600 hours below 68 degrees F.

In the meantime, our goal is to stop irrigation before a warm spell occurs (7 to 10 days with highs above 80 degrees F and lows near 70 degrees). Stopping irrigation soon enough before the warm spell should allow water stress to develop before the warm spell which will minimize any early bud development. In addition to stopping bud development, drought stress may also conserve freeze hardiness that the trees have gained during the current flower bud induction period.

Florida weather conditions continue to favorable this year for good citrus flower bud induction.

Southern areas will have accumulated about 500 hours below 68 degrees F by next Monday. Northern areas should have exceeded 600 hours by next Monday. Remember that the goal is to get to Christmas and/or above 900 hours below 68 degrees F before allowing initiation of flower bud differentiation.

Irrigation should be used sparingly until Christmas so that drought can be initiated by stopping irrigation if a warm spell occurs before then. Although 2 warm days are expected, Tuesday and Wednesday, this coming week should have generally cool temperatures, and therefore no potential for bud growth should occur this week. Growers should follow the NOAA 8 day forecast (http://www.crec.ifas.ufl.edu/CRECHOME/crecweather.shtml) later in the week to see if a warm spell is predicted for next week. If so, sufficient cool temperatures will have accumulated that a low to low-moderate initiation of flowering could start with the first significant warm spell. I would expect the first 2 or 3 buds from the shoot apex would start to differentiate if sufficient soil moisture is present during any warm spell that might occur from now until Christmas. Growers on deep sands should allow trees to reach mid-day wilt before irrigating, using perhaps 2 irrigations per week of about one hour duration. Trees in bedded groves should show wilt symptoms more quickly than those on deep sands and be irrigated accordingly, but sparingly.

Our goal, until Christmas, is to stop irrigation before a warm spell occurs (7 to 10 days with highs above 80 degrees F and lows near 70 degrees). Stopping irrigation soon enough before the warm spell should allow water stress to develop before the warm spell which will minimize any early bud development. In addition to stopping bud development, drought stress may also conserve freeze hardiness that the trees have gained during the current flower bud induction period. Another advantage of avoiding the initiation of early flower bud differentiation (the start of a bloom event) is that this will delay bloom date. For processed oranges this later bloom date should result in higher acidity levels in the Fall so that normal harvest dates can be reached with good Brix/acid ratios.

If a warm spell occurs around Christmas or when about 900 hours below 68 degrees F have accumulated, flower bud enhancing sprays such as urea or PO3 are appropriate to apply followed by increasing irrigation rates to stimulate growth. Minimum rates for urea should be 25 lbs N per acre (28 lbs is preferred, 63 lbs urea). PO3 materials may be applied at 2.5 qts/acre of a 26-28 % product. Such sprays, especially urea, will usually advance bloom date about one week. The best timing should be just before the predicted warm spell and not later than a couple of days into the warm spell. These sprays can be applied with good aerial application or by ground in 30 to 125 gal/acre.

If the bloom intensity potential is high when a warm spell causes initiation of flower bud differentiation, then a gibberellin spray (20 oz per acre of 4 % GA) may be appropriate to minimize the flowers per inflorescence in order to get a leafy bloom with stronger ovaries. This is primarily important for seedless cultivars in any year and mandarin hybrid types that are coming into the on-year of an alternate bearing cycle. GA should be applied at the end of the warm spell rather than before as recommended for urea. An early winter GA spray could stimulate shoot growth of the swelling buds if another warm spell comes soon. These buds or young shoots would then be much more susceptible to a freeze. If we can get to Christmas without a warm spell, then this hazard is not an issue. GA should be applied in 100 to 200 gal/acre total spray volume.

For those interested in applying either urea for Valencia or other processing oranges or GA for seedless cultivars or mandarins, materials should be purchased now and spraying equipment maintenance taken care of or custom spraying needs to be contracted.

Warning - The next 5 days will be relatively warm (low 80s) particularly across the southern half of the citrus zone. Although it may not be warm enough to initiate flower bud induction, the predictions are too close to initiating temperatures to take chances. It would be advisable to stop irrigating, if you haven't already, and allow some water stress to develop so that no growth is initiated at this time. The daily highs in the northern areas are predicted to be in the mid 70s. It appears that temperatures will get cooler again at the end of the week. If temperatures do cool off for a sustained period, look at 8 day forecast, then moderate irrigation can be resumed at the end of the week.

To date we have accumulated about 550 hours of inductive temperatures in the southern zones and over 600 in the northern-most zones. With the relatively warm week predicted, we will only accumulate another 100 hours this coming week. It would be desirable to accumulate another 200 to 300 hours after that before allowing the trees to initiate flower bud development. That should be accomplished by Christmas or New Years.

Until then, keep your eyes on the weather for warm spells and now also for freezes. Hopefully, we will not see one of those.

The next advisory should be posted early on Monday, 16 Dec. I may be late with the one following that, so watch the weather carefully on your own.

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #6 for 2002-2003-12/16/02

First the bad news - So much for my hoping you could develop some water stress by withholding irrigation. If anything, some of you may have been experiencing flooding conditions with all the rain. Now the good news - Temperatures were not as warm as predicted even in the southern half of the citrus zone. It appears, from our model, that initiating temperatures did not occur. The next 8 days should be satisfactory for continuation of inductive temperature accumulating, without sufficient warm weather to cause the beginning of bud break. The southern part of the industry should experience not more than 2 or 3 days near 80 and then it should become slightly cooler by next weekend.
To date we have accumulated about 600 hours of inductive temperatures in the southern zones and over 750 in the northern-most zones. With the predicted temperatures for the coming week, we should reach inductive temperature accumulations of 650 to 700 hours in southern areas and 800 to 850 in northern area by the end of the coming week. If the following week (Christmas) remains cool, northern areas should exceed 900 hours while southern areas should reach 800 accumulated hours below 68 degrees F. If a significant warm spell does not occur by New Year's day, trees should be in excellent condition to push into flowering at the first warm spell after that.
At that time, growers of processed oranges should consider whether to push their trees or try to hold them back for another 2 to 3 weeks. If additional rainfall does not prevent the ability to develop some water stress, growers should test the effect of withholding irrigation in order to get by an early January warm spell and then push their trees with irrigation at the time of the next warm spell.
Growers should be prepared to apply urea or PO3 just before the start of the first significant warm spell if soil moisture continues to be plentiful and there is no possibility of preventing bud break by developing some water stress. Previous experience indicates that flowering enhancement and increased yields can be obtained by applying either product after 850 to 900 hours of cool temperatures have accumulated.
Look for another update on Monday or Tuesday of next week.

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #7 for 2002-2003-12/22/02

This week, we have another 4 to 5 days with relatively warm (high 70s to low 80s) temperatures predicted for the southern half of the citrus zone. Like 2 weeks ago, it may not be warm enough to initiate flower bud differentiation, but it would be desirable to allow some water stress to develop so that no growth is initiated at this time. This assumes that little rain has fallen since week before last. There is a chance of rain predicted, but hopefully any rain will be towards the end of this warm spell. The high in the northern areas is predicted to be near 80 for one day only. These temperatures should not initiate flower bud differentiation. It appears that temperatures will get cooler again at the end of the week, but watch the weather forecasts.
To date we have accumulated about 720-740 hours of inductive temperatures in the southern zones, about 850 hours in central areas and 900 in the northern-most zones. Based on predicted temperatures, we should reach 800, 830 and 1000 hours in the southern, central and northern areas this coming week. At that time we will have acceptable flower bud induction levels in all but the southern areas, but it would be best if another week or two of cool weather occurred in all areas so that bloom date would be later in March.
For those planning to use urea or PO3 sprays on processing orange blocks, you should prepare to do that as soon as the next warm spell occurs and before mid-January. However, since most blocks have a light crop and induction levels are likely to exceed 1000 hours, good flowering should be expected whether you use flower enhancing sprays or not. Remember that these sprays, if used, need to be applied before the warm weather has occurred. Follow the NOAA 8 day forecasts linked to this website for prediction of the warm spell.
For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray may be useful at the end of the next warm spell that has 4 to 5 days exceeding 82+ degrees. These cultivars are likely to have excessive flowering with few leaves associated with the inflorescence. GA3 sprays should reduce the amount of flowering and increase the leaves in each inflorescence. Best timing for this sprays will be assessed as we see what temperatures are predicted each week.
See the next advisory before the new year.

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #8 for 2002-2003-12/29/02

This week, we have another 3 to 4 days with relatively warm (high 70s to low 80s) temperatures predicted for the southern half of the citrus zone. Again, it may not be warm enough to initiate flower bud differentiation, but our model predicts that a bloom may have been initiated in some districts. With the increased level of induction that now exists, it would be desirable to allow some water stress to develop, particularly in the southern areas, so that no growth is initiated at this time. This assumes that little rain has fallen. If it is not possible to develop some water stress, urea or PO3 sprays are recommended this following week in the southern areas. The high in the northern areas again is predicted to be near 80 for one day only. These temperatures should not initiate flower bud differentiation. It appears that temperatures will get cooler again at the end of the week, but watch the weather forecasts.
To date we have accumulated about 800 hours of inductive temperatures in the southern zones, about 1000 hours in central areas and 1050 in the northern-most zones. Based on predicted temperatures, we should reach 900, 1050 and 1100 hours in the southern, central and northern areas this coming week. We will have acceptable flower bud induction levels in all areas, but it would be best if another week of cool weather occurred in all areas, particularly the southern regions, so that bloom intensity will be a little higher and bloom date will be later in March.
For those planning to use urea or PO3 sprays on processing orange blocks, you should prepare to do that as soon as the next warm spell is predicted and before mid-January. However, since most blocks have a light crop and induction levels are now approaching or exceeding 1000 hours, good flowering should be expected whether you use flower enhancing sprays or not. Remember that these sprays, if used, need to be applied before the warm weather has occurred. Follow the NOAA 8 day forecasts linked to this website for prediction of the warm spell.
Since our model predicts that initiation of a bloom may have started in one or two locations, urea or PO3 sprays may be particularly beneficial in the southern areas. With induction levels near 1000 hours and if temperatures exceed the predicted (3 or 4 days near 80 degrees) this week, initiation of flower bud differentiation is likely to occur. The week following New Year's Day will be a good week to spray if you intend to. This is particularly important if the 8 day forecast indicates warm weather next week.
For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray may be useful at the end of the next warm spell that has 4 to 5 days exceeding 82+ degrees. These cultivars are likely to have excessive flowering with few leaves associated with the inflorescence. GA3 sprays should reduce the amount of flowering and increase the leaves in each inflorescence. Best timing for this sprays will be assessed as we see what temperatures are predicted each week. This coming week does not appear to be warm enough to consider GA sprays yet, but again if temperatures exceed predicted in southern areas then next week may be a suitable time.

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #9 for 2002-2003-1/5/03

This week, we have cool (highs <70s) temperatures predicted for all of the citrus zones. It should not be warm enough to initiate flower bud differentiation. Late in the week, high temperatures may reach the low 70s in the southern areas, but generally it will be too cold to get good uptake of either urea or PO3 sprays this week.
To date we have accumulated in excess of 900 hours of inductive temperatures in the southern zones, above 1100 hours in central areas and over 1200 hours in the northern-most zones. Based on predicted temperatures, we should reach 1050, 1230 and 1300 hours in the southern, central and northern areas this coming week. We will have acceptable flower bud induction levels in all areas at the end of this week.
As stated last week, our model predicts that initiation of a bloom has started in one or two locations. The predicted date of initiation of differentiation was 18 to 20 December with a predicted bloom date of 5 to 7 March. I also advised that urea or PO3 sprays might be applied to processing orange blocks with good crops in the southern areas if warm weather occurred. If those sprays were not applied, it will probably be too cold this week to apply foliar sprays. There is a long term forecast for a change in the jet stream and likelihood of colder weather after January 11th. If that occurs, no flower enhancement sprays are warranted. If, however, temperatures warm up next week, blocks with current heavy crops may still benefit from a spray.
For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray is advised at the end of the next warm spell that has 4 to 5 days exceeding 78 to 80 degrees. These cultivars are likely to have excessive flowering with few leaves associated with the inflorescence. GA3 sprays should reduce the amount of flowering and increase the leaves in each inflorescence. Best timing for this sprays will be assessed as we see what temperatures are predicted each week. This coming week will not be warm enough to consider GA sprays at this time.

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #11 for 2002-2003-1/17/03

All areas now have had initiation of some flower bud differentiation. Our model still indicates that only one flowering wave of buds has started to push. It takes the model about 7 to 9 days to evaluate a warm temperature event and decide if it was sufficient to push (initiate) some buds to start growth. We probably still have 80 % of the potential flowering buds to be initiated, but some more may have been pushed this past week in the southern citrus areas.
This week, we have cold temperatures predicted for all of the citrus zones over the weekend, but the southern areas will have 5 days with highs in the 70s with 3 or 4 days in the mid-70s. These temperatures, if they occur, should start the bulk of the remaining flower buds to initiate growth. The duration of higher temperatures in the northern half of the citrus area will be only 2-3 days in the lower 70s and 2 days in the high 60s. This will be a good time to apply either urea or PO3 sprays in the northern areas if you were planning to do so. Again, the most likely blocks to benefit are those with heavy current crops and especially Valencias with a good crop. For central and north Florida, the predicted temperatures may initiate flower bud differentiation since the flower bud induction levels are so high.
To date we have accumulated in excess of 1150 hours of inductive temperatures in the southern zones, above 1350 hours in central areas and over 1400 hours in the northern-most zones. Based on predicted temperatures, we should reach 1300, 1500 and over 1600 hours in the southern, central and northern areas this coming week. We will have excellent flower bud induction levels in the southern areas and perhaps excessive levels (snowball bloom potential) in all other areas at the end of this week.
For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray is advised at the end of the next warm spell that has 4 to 5 days exceeding 73 degrees. These conditions should be met this coming week in southern areas if predicted temperatures occur. The above cultivars are likely to have excessive flowering with few leaves associated with the inflorescence. GA3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. Best timing for this sprays in central and northern zones will be assessed as we see what temperatures are predicted each week. We will report an assessment of appropriateness for this spray in the northern area on Friday of next week.
For those growers testing our flower bud induction intensity-bloom date model, you may find that the current version will not provide a second initiation of differentiation to bloom curve for northern areas or central areas that exceed 1500 hours of cool inductive temperatures. This is a programming problem because we did not anticipate inductive levels exceeding 1500 hours while there were still flower buds to have growth initiated. We are working on a patch that may be provided or discussed in these advisories. We will provide information about the second wave of flower bud growth for these areas one way or another.
Lets be bold. I predict that the minimum temperatures tomorrow morning likely will not reach the predicted lows. Although the jetstream dipped more strongly from North to South through the Midwest towards Texas yesterday, it has apparently stabilized so that air flow will continue to be mostly lateral, West to East, across the Gulf of Mexico. This should continue to moderate temperatures reaching Central and Southern Florida. Another good sign is that temperatures in the central to northern citrus stopped dropping about 11 am to noon and were holding fairly steady through 2 pm. Lets keep our fingers crossed.

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #12 for 2002-2003-1/24/03

FREEZE ON FRIDAY - Temperatures generally were in the upper 20s to low30s. Most of the tree can withstand a short period at these temperatures after the cold weather that the trees have been subjected to. We don't know about the buds that have already started to swell. We rechecked on terminal buds at Lake Alfred yesterday. They now show that about 50 to 70 % of the terminal 3 buds had some swelling indicating start of growth. This compares to 10 to 20 % of these buds showing some bud swell when they were checked 2 weeks ago. Many of the buds in these shoot positions had enough additional growth from 2 weeks ago that they could be seen without use of a hand lens. We don't know how susceptible these buds were to freezing temperatures compared to the shoots and trees in general, which should have withstood temperatures as low as 21 to 22 degrees F. We will check some of these swollen type buds on Monday or Tuesday from more northern sites near Avalon and Tavares.
All areas now have had considerable initiation of some flower bud differentiation. Our model indicates this and shoot terminal bud examinations confirm this. Because of the very high accumulated cool temperature hours, many more buds down the spring and summer shoots than the first 3 buds on spring or summer shoots will be flower buds. If the projected warm spell projected for the end of next week extends for 3 or 4 days, many of these buds should start to grow (swell). That should constitute our second major wave of initiation of flower bud differentiation.
Later next week while temperatures in central and northern Florida are in the low to mid-70s will probably be a good time to get reasonable uptake of either urea or PO3 sprays. Again, the most likely blocks to benefit are those with heavy current crops and especially Valencias with a good crop. But remember that the very high levels of induction in central and northern areas reduces the likelihood that these sprays will provide a benefit this year.
To date we have accumulated in excess of 1300 hours of inductive temperatures in the southern zones, above 1500 hours in central areas and over 1600 hours in the northern-most zones. These are very high levels of induction for Florida before the initiation of a second flower bud differentiation wave. Weather forecasts make it likely that at least another cool week will occur raising those levels even higher.
For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray is advised at the end of the next warm spell that has 4 to 5 days exceeding 69 to 72 degrees, note that these temperatures are now lower than stated previously because the intensity level of induction is now higher. These conditions may be met this coming week in northern as well as southern areas. The above cultivars will have excessive flowering with few leaves associated with the inflorescence. GA3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. Best timing for this sprays in all areas will be after next week if temperatures are as high as predicted for the end of next week and these temperatures continue for 4 or 5 days. We will confirm that conditions are adequate to apply a GA spray at the end of next week.
For those testing our induction-flowering date model, we are just getting the model updated for the high induction levels being experienced. In any area that shows more than 1500 hours of temperatures less than 68 degrees F, the current version will not show the next and final initiation of flower bud differentiation along with the projected bloom date. Hopefully, we will have an adjusted version to download early next week. Alternatively, I will report those conditions and projected bloom dates for the major areas.

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #13 for 2002-2003-1/31/03

REMINDER TO ALL RIDGE CITRUS GROWERS - NITRATE BMP PROGRAM - The permanent rules are now in place for the voluntary program administered by the FDACS Office of Water Policy. Even if you were signed up for the interim measure, you have to sign-up again in order to qualify for the liability exemption provided by the program. All of the information is available on the DACS Website of the Office of Water Policy, which is listed in the links provide by this Website (http://www.floridaagwaterpolicy.com/ ).
All initiation of flower bud differentiation should be complete during this warm spell. Because of the very high accumulated cool temperature hours and this significant warm spell, all remaining buds on last year's spring and summer flush that can be expected to be flower buds will have initiated growth now. This second wave of flower bud differentiation may not be as large as the first wave that was initiated in late December. A report from Ft. Pierce-Vero Beach indicates that as many as 6 buds down the shoot are already swelling from new growth. In a heavy flowering year, 8 or 9 buds down the shoot might be expected to become flower buds.To date we have accumulated in excess of 1500 hours of inductive temperatures in the southern zones, above 1700 hours in central areas and over 1850 hours in the northern-most zones. These are very high levels of induction for Florida before the initiation of a second flower bud differentiation wave.
For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray is advised Monday to Wednesday next week. The above cultivars will have excessive flowering with few leaves associated with the inflorescence. GA3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. As stated previously, the use of urea or PO3 to increase flowering is probably not necessary this year on even fairly heavily cropped blocks.
For those testing our induction-flowering date model, we expect to have the model updated late today for the high induction levels being experienced. In any area that shows more than 1500 accumulated hours of temperatures less than 68 degrees F, the current version will not show the now occurring and final initiation of flower bud differentiation along with the projected bloom date. Hopefully, we will have the adjusted version ready to download early next week. Alternatively, I will report those conditions and projected bloom dates for the major areas in a new advisory early next week. My guess is that we will have a major bloom wave peaking the first week of March and a smaller, second wave peaking the 4th week of March. We will see what the model says next week.

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #13 for 2002-2003-2/4/03

Initiation of flower bud differentiation for second flowering wave is completed during this warm spell. The intensity of the second wave of flowers will be fairly heavy. Flowering in the first wave, full bloom projected to be 5 to 10 March, will be primarily in the first 3 to 5 terminal bud positions, while the second wave, full bloom projected to be last week of March, will be in the 4 to 8th or 9th bud positions. I expect flowering into these bud positions because of the high accumulations of hours less than 68 degrees F. Counts of growing buds from Hamlin trees near Clermont had 60 % or more buds not growing in positions 2 through 8 in samples taken on 1/31, just as the second wave of bud growth was starting. These samples taken after the freeze has some bud edges singed, but all buds were still healthy. In a lower central flatwoods citrus area, Hamlin buds from a sampled grove had fewer buds showing any growth than the Clermont grove. On the other hand, Valencia trees at this same site had more buds growing (60 % of first 2 buds and about 40 % of 3rd bud position). Even so, there are still more buds that should produce flowers than were started in the first wave.
At the time of initiation of differentiation in the second wave of buds, there were 1250 to 1290 hours accumulated in the southern zones, above 1500 hours in central areas and over 1700 hours in the northern-most zones. These are very high levels of induction for Florida before the initiation of a second flower bud differentiation wave.
For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray was advised for this week. The above cultivars will have excessive flowering with few leaves associated with the inflorescence. GA3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. As stated previously, the use of urea or PO3 to increase flowering is probably not necessary this year on even fairly heavily cropped blocks. Also, it is probably too late to apply these products for flowering enhancement now.
Our induction-flowering date model is working again. Although it does not give the cool hours accumulated above 1500, it does project the second wave of initiation and predicts flowering dates. Cooperators should receive a CD with the revised program or information to a download site. The projected bloom dates by location as of now are: Tavares-3/19 & 4/4, Avalon-3/3 & 4/3, Lake Alfred-3/7 & 3/31, Ona-3/6 & 3/24, Ft. Pierce-3/12 & 3/29, Immokalee-3/11 & 3/30.
We would appreciate if everyone that is following these advisories would observe and report the average full bloom date(s) of their cultivars with information about location. How close are these projections to actual bloom dates that occur? Also, please report, if 2 bloom waves are observed, generally which buds on the shoots contributed flowers to each wave or if different parts of trees or different trees contributed to the early March and late March waves.
We will start spacing these advisories out to once every two weeks until bloom, with mostly reports of flower bud growth. If anyone observes a general bloom earlier than the first week in March, please let me know. This will help us to make corrections, if needed, for various factors in the bloom date prediction model. Watch for possible cold temperatures next week.

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #15 for 2002-2003-2/21/03

Estimated dates of full bloom
Our model predicts that full bloom for a first wave of bloom should be around March 8-9 in southern areas, March 3-4 in central areas and March15-18 in northern areas for round oranges. The model fits the data used to develop it within + or - 5 days. The model predicts that a second wave of flower buds should reach full bloom near the end of March. It appears on many trees that this second wave may have many fewer flower buds involved in it, since so many buds are pushing now. Observations in this area suggest that bloom dates might be a little ahead of the estimate. Hamlins and Valencias have terminal flowers at small pop-corn and lots of pin-head visible. Mandarins are clearly behind these in stage of development, as expected. Some weak trees in the Ft. Pierce area were in full bloom on Wednesday, but other trees were perhaps a week to 10 days from full bloom. I would appreciate observations of full bloom dates on healthy trees from anyone making those observations. Please email to: albrigo@crec.ifas.ufl.edu . Indicate the cultivar and general location of the grove with your estimate of full bloom date.. This will help us in fine tuning the model if needed.
Early bloom foliar nutritional sprays
The few blocks I have looked at have mostly mixed inflorescences with a good number of leaves and flowers. These have a better chance to set fruit than flower buds with only flowers. On the other hand we expect heavy flowering so a lot of competition should occur and foliar nutritional sprays may help to improve fruit set. For those planning to put on an early bloom foliar nutritional spray, we recommend application at 5 to 10 % open flowers. That may occur next week. If you have several blocks to spray, you may need to start early next week and perhaps finish in full bloom. Consider that mandarin blocks will bloom last and navels usually bloom a little earlier than other oranges in trying to develop the best schedule.
A number of people observed accelerated older leaf drop and some additional twig dieback when 2 to 2.5 qts of any of the PO3 products were mixed with KNO3 or other N-P-K products last bloom period. Until we know more about these tank mixes, it may be better to use either PO3 with low levels of other nutritionals at bloom or a traditional foliar N-P-K mix at 10 to 15 lbs of N/acre. No phytotoxicity problems were observed when PO3 products and KNO3 at 10 to 15 lbs per acre when applied at the postbloom timing.

FLOWER BUD INDUCTION ADVISORY #16 for 2002-2003-3/27/03

POST-BLOOM UPDATE - Estimating dates of full bloom
Our flower induction-bloom date model first predicted that the full bloom date for a first wave of flowers would be March 12-13 in southern areas, March 6-7 in central areas and March15-18 in northern areas for round oranges. The model predicted that a second wave of flower buds should reach full bloom near the end of March. As the flower bud development progressed into early February, the program moved the predicted dates of bloom up about 5 or 6 days so that central areas were expected to be in full bloom about March 1st. Our observations around this area put the actual bloom dates closer to the original 6 to 10 March prediction. Southern area trees bloomed a little behind the central ridge as predicted. While some weak trees bloomed early, most trees were closer to the original predicted dates. We will have to observe flowering dates for a couple more years and compare these to predictions before we can conclude how accurate the program is. Last year, the predicted dates appeared to be very close to the actual dates and this year's predictions were still within a week.
For all of the citrus areas in the state, most available buds initiated differentiation and reached full bloom in the first flowering wave. This left almost no buds to respond to the second warm spell for a bloom in late March. I did see some branches and one tree in a Valencia block in Avon Park that had a noticeable amount of the second bloom. In south Florida near Immokalee, I saw groups of trees within some blocks that had mostly the second bloom wave and were in full bloom. These were the zones of poorest soil and may have been drought stressed during the first initiating warm spell in late December due to low available soil moisture at that time. Other than these cases, every other block or report has been of almost exclusive first wave flowering.
Flowering progressed rapidly by all reports and observations. Up to 15 bud positions had inflorescences on strong summer shoots. Most inflorescences had a few flowers with several leaves. The good balance of new leaves with the flowers was probably because the first wave of flowering was initiated to differentiate after about 840 hours of cool temperature accumulation rather than the 1300 or so that had accumulated by the second warm spell. At that later time, mostly generative inflorescences, without leaves, should have been produced. This was observed March 26th in the trees on poorer soil that had mostly the second wave of flowering.
So far, so good on development of the new crop. There was a good bloom with a good ratio of leaves to flowers. No one has reported any significant PFD in spite of rains during bloom. Weather during flowering and the first drop wave has been fairly cool with good soil moisture levels thanks to the rains. In general we should have large fruitlet numbers going into the later drop period. This will result in a heavier than normal May-June drop, but there should be more fruitlets remaining after that than usual. The one negative factor so far is that bee activity on citrus flowers was lower than expected. It may be that nectar levels or sugar concentration were lower than normal. Unfortunately, we were not monitoring these factors this year. Watch particularly for heavy drop of fruitlets the next 3 weeks in hybrids that require cross pollination. This would indicate that poor pollination and ovary fertilization occurred.
Last year at bloom, many people observed phytotoxicity from sprays combining PO3 with KNO3 and sometimes other products. We have done a test this year to see if the same susceptibility existed. We included a PO3 rate that was half again as much as recommended (3 lbs per acre rather than 2). Only a slight amount of burn was observed and this occurred only at the excess rate ( three lbs PO3/ac) and when KNO3 with or without urea was added to the spray mix. It appears that last year's sensitivity was a one year occurrence, but we are not sure why it happened. No sensitivity occurred last year when similar sprays were applied post-bloom.
I would appreciate observations of full bloom dates on healthy trees from anyone making those observations.

FLOWER BUD INDUCTION ADVISORY #1 for 2001-2002-11/16/01

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS 
The following information has been developed as part of the Decision Information System for Citrus. 
L. Gene Albrigo, Horticulturist
Citrus Research & Education Center, Lake Alfred, FL 

It is the time of year to start following citrus flower bud induction conditions for the coming year's bloom. Cool weather stops growth and then promotes induction of flower buds as more cool weather accumulates. A warm spell can then initiate differentiation which after sufficient days of warm temperatures leads to bloom. The meteorologists say that this winter in Florida will be cooler than normal, an El Nino year. Potentially sufficient cool temperatures should accumulate, below 68 degrees F., to induce adequate flower buds for an economic crop. Sufficient flower bud induction under Florida conditions is achieved when total accumulated cool hours of 850 to 1000 hours below 68 degrees F. occurs without interruption before a warm spell triggers growth, i.e.., 7 to 12 days with max. temperatures > 70 to 75 degrees F. So far this year sufficient cool weather has occurred to slow down or stop vegetative growth on mature trees, 160 to 190.hr < 65 degrees F. in southern districts and 230 to 250 hr < 65 degree F. in northern districts. This information is available on the Florida Automated Weather System (fawn.ifas.ufl.edu).

The major concern for the next 45 days is the possibility of an early warm spell that will initiate differentiation of easily induced flower buds or push vegetative buds to grow. Some flower buds will be induced in the range of 300 to 600 accumulated hr < 68 degrees F. These early warm events therefore result in many buds remaining that can be induced by later cool spells and multiple blooms will occur. If winter bud break is not prevented in Florida, multiple blooms occur in about half of the years. The early time period in which some bud growth can occur and lead to multiple blooms is roughly Thanksgiving to Christmas. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is to allow water stress to develop during this time period.

If no rains interrupt a mild stress condition of the citrus tree, buds will not grow in response to warm temperatures. These warm spells in the late fall-early winter usually last less than two weeks. A warm spell is predicted for the Thanksgiving week ( www.crec.ifas.ufl.edu, click on weather links and 8 day forecast). After a warm spell has passed, trees again can be watered to minimize fruit water stress. Although no weather prediction is guaranteed even by the meteorologist, rains in the winter usually come on the fronts of cool spells. Therefore, the chances of applying water stress to prevent an early flower bud differentiation is reasonably good for some warm spells.

With the shallow soils in bedded groves, it is relatively easy to reach sufficient stress to suppress growth by withholding irrigation for a few days. In deeper sandy soils, 2 or more weeks may be required. To minimize the time to initiate water stress, the soil should be allowed to dry out in late fall so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied as needed until a weather prediction indicates a warm spell is expected. At this time irrigation should be shut down. For deep sands, the soil needs to be dried out and left that way until at least Christmas so that no growth can occur. This may be risky for Hamlin or other early maturing cultivars that tend to drop fruit near harvest.

Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus'. This system will be available for testing with a limited number of growers this winter. A discussion of this system will occur in a seminar at the Citrus Research and Education Center at 1:30 on Monday, November 19th. The background data and system will be presented as an exit seminar by PhD student Juan Valiente.

Future advisories will update accumulating weather effects on flower bud induction and methods for enhancing or reducing flowering intensity as conditions and cultivars dictate.

FLOWER BUD INDUCTION ADVISORY #2 for 2001-2002-11/24/01

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS 

The following information has been developed as part of the Decision Information System for Citrus. 
L. Gene Albrigo, Horticulturist 
Citrus Research & Education Center, Lake Alfred, FL

See the previous advisory for background information. Cool weather stops growth and then promotes induction of flower buds as more cool weather accumulates. A warm spell can then initiate differentiation which after sufficient days of warm temperatures leads to bloom. In the first advisory, I mistakenly stated that this winter in Florida would be cooler than normal, an El Nino year. It is in fact supposed to be a neutral year. By January sufficient cool temperatures may accumulate to induce adequate flower buds, but so far temperatures have been moderately warm. We are a long way from a total accumulation of 850 to 1000 hours below 68 degrees F. so that sufficient bloom will occur to result in an economic crop. So far this year cool weather hours have only reached 230 to 270 hr < 65 degrees F. in southern districts and 315 to 330 hr < 65 degree F. in northern districts. These cool temperature hr accumulations are at least 120 hr less than last year by the same calendar date. This information can be accessed on the Florida Automated Weather System (fawn.ifas.ufl.edu). Of more concern is the continued accumulation of temperatures with daily maxima of near to > 80 degrees F. With continued irrigation these temperatures may stimulate a fall flush of growth. Any buds that sprout now are lost as potential flower buds for induction later in the winter.

The major concern for the next 40 to 45 days continues to be the possibility of this early warm spell initiating differentiation of easily induced flower buds or pushing vegetative buds to grow. Some flower buds will be induced after 300 to 600 hr < 68 degrees F accumulate. A warm spell can then result in a weak flowering event leaving many buds that can be induced by later cool spells and multiple blooms will occur. In Florida, without winter growth control, multiple blooms occur in about half of the years. The critical time period in which bud growth starts too early is Thanksgiving to Christmas. The only practical way to reduce the chance of multiple blooms is to allow water stress to develop during this time period.

Citrus buds will not grow in response to warm temperatures if sufficient water stress is present. Warm spells in the late fall-early winter usually last less than two weeks. However, the current warm spell is predicted to last for another 5 to 6 days (( www.crec.ifas.ufl.edu), to see predicted weather click on weather links and 8 day forecast). Mature, well watered trees with light to moderate crops may push a fall flush of growth. Younger trees are likely pushing a vegetative flush of growth.

With the shallow soils in bedded groves, it is relatively easy to reach sufficient stress to suppress growth by withholding irrigation for a few days. In deeper sandy soils, 2 or more weeks may be required. To minimize the time to initiate water stress, the soil should be allowed to dry out to the wilting point in late fall. For bedded groves, minimum irrigation then should be applied until the weather is predicted to turn warm. At this time irrigation should be shut down giving 6 to 7 days for water stress to develop. For deep sands, the soil needs to be dried out and left that way until at least Christmas so that no growth can occur. This may be risky for Hamlin or other cultivars that easily drop fruit near harvest. After a warm spell has passed, trees again can be lightly irrigated to minimize fruit water stress and the chance of fruit drop. Until the current warm spell ends, the best procedure to increase flowering is to hold the trees in a low level of water stress. Water stress is not favored as a flower induction procedure for Florida since more than 40 days of stress are needed to reach a moderate level of flowering. Short periods of water stress to prevent early bud sprout do appear feasible however and some growers have used this procedure successfully in previous years.

Since this winter may have relatively low accumulated hours below 68 degrees F, foliar urea applied just before a Christmas to New Year warm spell may be beneficial to enhance flower bud induction. We will discuss this treatment and update flower bud induction levels next week.

Much of what has been stated above has now been incorporated into a 'Flowering Expert System for Florida Citrus'. This system will be available for testing with a limited number of growers this winter. We still need some cooperators for testing this system. Contact Gene Albrigo ( albrigo@lal.ifas.ufl.edu ) if you are interested. A training session will occur in one or two weeks

FLOWER BUD INDUCTION ADVISORY #3 for 2001-2002-12/2/01

The continued warm winter is adversely affecting flower bud induction (FBI) for next years crop. Little cool temperatures for FBI have occurred and warm temperatures are predicted for the next week also. Even the little accumulated cool temperatures (about 400 hr) may be of little value since daily maximum temperatures have been above 80o F almost every day. In many groves where irrigation has continued at application rates recommended to prevent water stress, buds are pushing for an early Winter flush. This situation further reduces potential for next year's crop as those buds could have become flower buds later in the Winter. Some grower's have shut down irrigation. Water stress can prevent growth during a warm spell and sufficient drought stress can induce flower buds. This process, however, appears to require 35 to 45 days of water stress to provide a reasonable level of flowering. For Hamlin trees with fruit still on the tree, allowing excessive water stress to develop is risky as excessive fruit drop may occur and photosynthesis is reduced which limits sugars to increase fruit Brix. If and when cool temperatures do occur, most daily temperatures below 69o F, flower bud induction can proceed from cold induction conditions adding to any water stress effects on FBI. Irrigating during cold periods will not stimulate bud-break, but it may be advisable to limit irrigation so that water stress can easily be reintroduced. Trees may require water stress again after some cool weather occurs if the cool period is insufficient or the warm period occurs too early and will result in flower bud differentiation (growth) leading to an early bloom of processing oranges.
Conditions are not favorable for applying a winter urea or phosphorous acid spray to enhance FBI. These sprays are not effective to enhance FBI until some natural induction has occurred. Our best results have occurred when foliar sprays of these materials were applied after at least 800 -900 hours below 69o F had accumulated. As stated earlier, accumulation of these lower temperatures up to now may need to be discounted due to high daytime temperatures.
An early bloom in trees with fruit intended for processing may lead to early maturation, with low Brix and low acidity as occurred this season. A possible way to avoid this may be to apply water stress during any early January warm spell in order to delay initiation of differentiation until late January. This idea merits examination if conditions warrant doing so this season. Continued lack of low cool temperatures for induction may dictate using water stress in January anyway if rainfall does not counter this procedure.
Monitoring flower bud induction and bloom date along with some strategies for altering both are now incorporated in a ‘Florida Citrus Flowering Expert System' which will be introduced to some grower cooperators next Friday. Contact Dr. L. Gene Albrigo at albrigo@lal.ifas.ufl.edu if you are not in that group and wish to be. A limited number of additional cooperators may be added.

FLOWER BUD INDUCTION ADVISORY #7 for 2001-2002-1/7/02

Cool temperatures for FBI have continued and are predicted to continue for the next week. For all groves that were not placed in water stress conditions in late November-December, the earliest date that trees should be allowed to start flower bud differentiation is still in late January (27th). After this date, trees can be allowed to respond to a warm spell by providing adequate soil moisture for growth (resume full irrigation). A urea or phosphorous acid spray should be applied the week before the warm spell occurs in which the trees are allowed to begin growth. Since many of the terminal end buds on last year's spring and summer flush have started to swell, any additional induction that can be achieved will increase the likelihood that buds further down the shoot will be flower buds. For some locations, our new ‘Citrus Flowering Decision Support System' predicts that the differentiation of a bloom started in late December. I think that this flush will be mostly vegetative, but time will tell.
For groves in which water stress was applied in November and December, the trees may have additional flowering induction from the combination of water stress and some cool temperature accumulation. Unfortunately, the level of water stress required to accomplish that may not have been achieved by most of us that were trying to regulate our irrigation. In a block of 6 year old Hamlin and Flame trees on a deep sand where we reduced the amount of water applied per irrigation and allowed trees to show wilt by 10 am before reapplying water, we have about 60 % of the first 4 buds from the terminal end swelling with a few buds in early flush stages. If none of those buds produce flowers, I estimate that we have lost about 50 % of our flowering potential. It is not easy to determine if buds are swelling in comparison to the bud remaining quiescent. The bud scales will be swollen and a lighter (lemon green) color than the non-growing buds. On grapefruit trees, swelling buds will be pubescent. Those that are pushing new growth are easy to evaluate. Based on our experience, I advocate holding all trees back from any further bud growth until February if it is possible.
Unless cool temperatures continue well into February, urea sprays are advised just before a projected warm spell and should be applied at 25 to 28 lbs N per acre in 10-15 (aerial with good spray distributors), 25-30 (ultra low volume), or 50-125 (speed sprayer) gal/ac of water. Speed sprays can be calibrated for as little as 50 or 60 gal/ac at 4-5 mph if large acreage needs to be covered. High speeds do increase risk of operator driving error. Phosphorous acid should be applied at the equivalent of 2.6 quarts of 26-28 % P product in similar gal/ac as recommended for urea sprays.
If accumulated hours get above the 800 level counting from 19 December 2001 seedless cultivars and mandarins coming into the on-year may have sufficient flowering without enhancement sprays. We will continue to monitor cool weather into February since the potential levels of flowering and needs for flower bud induction altering sprays will have to be reevaluated if cool weather persists until then.
Contact Dr. L. Gene Albrigo at albrigo@lal.ifas.ufl.edu if you have questions or observations about trying to maintain light stress on citrus trees under Florida conditions.

FLOWER BUD INDUCTION ADVISORY #8 for 2001-2002-1/11/02

Cool temperatures for FBI may continue the next week in northern districts, but sufficient warm temperatures are predicted for flatwoods areas and probably the southern ridge (south of Avon Park) that initiation of another set of flower buds should occur this coming week. For these areas, now is the time for urea or PO3 sprays. For Northern areas, trees may slide through the marginal temperatures and accumulate more cool temperatures before bud growth starts. Sprays to enhance flower buds could be applied now in these areas, but if daytime highs stay in the low 70s and turn cooler in about 4 days as predicted, growers can wait for the next warm spell before spraying in these northern areas.
Urea sprays should be applied at 25 to 28 lbs N per acre in 10-15 (aerial with good spray distributors), 25-30 (ultra low volume), or 50-125 (speed sprayer) gal/ac of water. Speed sprays can be calibrated for as little as 50 or 60 gal/ac at 4-5 mph if large acreage needs to be covered. Phosphorous acid should be applied at the equivalent of 2.6 quarts of 26-28 % P product in similar gal/ac as recommended for urea sprays.

FLOWER BUD INDUCTION ADVISORY #9 for 2001-2002-1/18/02

Sufficient warm temperatures to initiate flower bud differentiation are occurring or predicted for all citrus areas. For all areas were urea or PO3 sprays were planned, they should be applied soon if they have not already been done. For Northern areas, sprays may be effective if sprayed well into next week.. For Southern areas, sprays to enhance flower buds need be applied by early next week to have a reasonable chance of being effective.
In most groves examined some buds are pushing from differentiation and bud swell that started by 20 December. There are a few flowers in that flush, usually not more than one per inflorescence if present at all. Most of the flowers will be in the flush being initiated now. I predict that due to the low accumulation of cool temperatures the inflorescences will have many leaves and few flowers. Therefore a flower enhancing spray is warranted for most cultivars if you can get it on soon. The good side of low flowering with many leafy inflorescences is that set should be high. Seedless cultivars and mandarins that had a light crop last year may have about the correct number of flowers due to the low induction levels. It is my best guess that in these cases neither flowering enhancement nor reduction (gibberellic acid) sprays should be applied.
Where urea is used, sprays should be applied at 25 to 28 lbs N per acre in 10-15 (aerial with good spray distribution (powered spray distributors)), 25-30 (ultra low volume), or 50-125 (speed sprayer) gal/ac of water. Speed sprays can be calibrated for as little as 50 or 60 gal/ac at 4-5 mph if large acreage needs to be covered. Phosphorous acid should be applied at the equivalent of 2.6 quarts of 26-28 % P product in similar gal/ac as recommended for urea sprays.
Currently, bloom dates are predicted to be about 5-10 March and 25 March to 1 April. This means the blooms will overlap. Periodically, there will be updates of the projected bloom date from our new flowering decision support program. Also, observations of flowering levels will be presented when flowers are visible. I would appreciate email observations of bloom characteristics from growers in all districts.

FLOWER BUD INDUCTION ADVISORY #10 for 2001-2002-1/29/02

Sufficient warm temperatures occurred prior to December 18th and again from January 18-20 to 25-27 January to initiate 2 flower bud differentiation sets in all citrus areas. Currently, if unseasonably warm weather continues, bloom dates for these 2 sets of floral buds could be about February 17th and March 20th. It is not likely that additional flowering flushes will occur this season.
Because the daily maxima were above 80 degrees F almost every day from November 17 until 18 December, the initiation process of that set of buds may have started several days earlier than 18 December. Daily minima were near or above 60 degrees C from November 17th also. This could result in an even earlier bloom for those buds than mid-February, occurring mostly in the terminal 2 or 3 bud positions on last summers shoots.
Many growers report seeing flush and report that some of it has one or two pin-heads flowers visible. This is better than our worst prediction, that no flowers might occur in the first flush. Still it appears that there will be few flowers and mostly leaves in the first bud sprouting.
Most of the flowers will be in the second flush that started to differentiate a week ago. Due to the low accumulation of cool temperatures between the two flushes, the inflorescences probably will have many leaves and few flowers. Although more flowers would be desirable, better set occurs when there are several leaves associated with the flowers in each inflorescence.
Since the differentiation process is now well underway, flower enhancing sprays of urea or phosphorous acid are not likely to work.
In summary, peak bloom dates are now predicted to be about mid- to late February and 20 to 25 March. This means the blooms will overlap with some flowers appearing throughout the period from mid-February to late March. The first bloom should be a very light flowering with 1 or 2 flowers per inflorescence when flowers are present. Periodically, there will be updates of the projected bloom date from our new flowering decision support program. Also, additional state-wide observations of flowering levels will be presented as the inflorescences develop. I would appreciate email observations of bloom characteristics from growers in all districts.

FLOWER BUD INDUCTION ADVISORY #1 for 2000-2001-12/1/00

As in the last two winters, we will attempt to relate the cool temperature accumulation and warming spells to the flower induction levels as the winter progresses. Weekly advisory reports on the accumulation of cool temperatures, generated from the FAWN weather system, and recommended spray timing for winter sprays will continue until mid or late January, after which it is less likely that any attempts to alter flower bud induction will succeed. Advisories will appear on the Citrus Research and Education Center Web Page. The website is at http://www.crec.ifas.ufl.edu (look under Grower Aids). This information will also be forwarded to County Extension offices and other publishing sources. It should be noted that waiting for these written announcements might cause delays in management practices, which may result in missing an important timing window.
The 2000-2001 winter
Winters in the 1990's have been the warmest on record, with the last three among the warmest. According to the National Weather Service, the 2000-2001 Fall-Winter weather in Florida is expected to be warmer than normal (1961-1990), but slightly cooler than the last three years. This provides the potential for more adequate period of cool temperatures than what we have received during the last three years. A prolonged period of cool temperatures (below 70 o F) is necessary for good flower bud induction to occur. Warm periods can initiate bud differentiation (growth) and discontinue the induction process.
In contrast with other Gulf Coast States, Florida is not expected to receive more precipitation than usual. These are good news as, in addition to temperature stress, flower bud induction may be complemented with drought stress. Drought stress constitutes the other natural process for flower bud induction in citrus. Drought stress must be sufficient to stop tree growth and cause induction to proceed. If little rain occurs during a warm winter significant drought stress may develop without irrigation. A combination of both processes may be used to achieve adequate flower bud induction. Withholding irrigation for at least 30 to 40 days should be long enough to increase flower induction. The time to which trees should be withdrawn from irrigation, depends on soil type, depth, and whether the grove is bedded or not. Drought stress also can stop initiation of differentiation of potential flower buds if intermittent warm periods occur during the winter. Multiple blooms may be avoided by keeping the trees drought stressed until they are ready to initiate flower bud differentiation in mid-January.
But not everything is good news, despite the fact that forecast probabilities favor warmer than normal (1961-1990) conditions in much of the southeast this winter, the National Weather Service expects more days with minimum daily temperature below freezing compared to the past 3 winters. This means that the changes of a freeze are increased. Precautions should be taken to face the likelihood of a Florida freeze.
So far this winter…
The Fall of 2000 has been cool and excellent induction temperatures have occurred. From October 1st until December 7th, we have had 850 hours below 70F, which is 300 more hours than last year (1999-2000). These are also more than 500 hours from the previous year (1998-1999) for the same period the year before. You may remember that in the spring of 1999 we had an extended flowering period that lasted for over three months. The experienced low temperatures should be more than enough to stop vegetative growth and get the flower bud induction process underway.
Although these are good news, it also means that bloom management should start earlier than the last two years. The occurrence of a warm spell may trigger unwanted growth at this stage. If a warm spell forces growth, this will be mostly vegetative. The few flowers forming would encounter lower temperatures and therefore low fruit set.
Bloom management.
Flowering may be managed in a variety of ways.
Drought stress. Cold temperature stress may be coupled with irrigation withdrawal (drought stress) to achieve increased stress and therefore greater induction levels. Drought stress can also be beneficial, as it will prevent the onset of growth during warm spells. If growth is not prevented prior to the full induction level, there will likely be an extended flowering period, which is not desirable.
Drought Stress on Bedded groves. Moderate drought stress may be maintained on flatwood bedded groves with the irrigation system shut down. By maintaining the water-table just below the bottom of the water furrows, daily stress can occur with some recovery each night from moisture taken up by the tree roots that extend to near the bottom of the water furrow. If the water table is one or more feet below the water furrow, severe drought stress will occur if irrigating is stopped and there is no rain. Also, if severe root pruning occurred due to high water levels during the previous two years, then a water table at the bottom of the furrow may still result in a severe stress level. Visual observation of temporary leaf wilting can be a good indicator of proper stress. Wilting by 10 or 11 am. and recovery overnight is ideal.
Drought stress on deep-sandy soils. Drought stress is much more difficult to develop on deep sandy soils due to the deeper rooting zone. Two or three weeks may be required on deep sands in order to reach an adequate level of stress to begin flower bud induction. Drought stress can be used on Valencia trees, trees already harvested or Hamlin trees that will be harvested during December. Trees with fruit intended for fresh market should not be subjected to severe drought stress. Valencias hold their fruit very tightly, but Hamlins for later harvest or Pineapple oranges are likely to experience excessive drop of the current crop if subjected to even moderate drought stress.
If one or more winter-time rain fronts negate the attempt to maintain water stress, the associated cool weather behind the front (a typical occurrence) may provide some cool temperature induction. The issue will be whether enough induction has occurred.
Winter sprays of stress-boosting chemicals. Even in cool years of good induction conditions, winter sprays of stress-boosting chemicals can provide benefits by increasing flower bud induction and subsequently yields of at least Valencia trees on flatwood soils. Four years of tests on Valencia oranges on bedded grove sites have shown a consistent enhancement of total yield and pounds solids per acre from urea or potassium phosphite (PO3) sprays (Albrigo, Proceedings Florida State Hort. Soc., 1999, in press). Some grower tests using these materials have provided similar increased flowering and yield results on other cultivars as well as Valencia trees.
After some cool temperature induction or 30 days of drought stress, foliar sprays of either 50 to 60 lbs of spray grade urea per acre or 2.6 quarts of 28 % P as potassium phosphite per acre can enhance flower bud induction. Foliar sprays of urea or phosphorous acid products presumably work only if some induction has taken place from natural cold or drought stress. Lovatt, et al. (1988) demonstrated this for foliar sprays of low biuret urea. In our previous tests, the timing of this spray was between Christmas and January 5th. In years of strong El Nino or La Nina events, suitable timing may be earlier or later. In any case, the timing must be before significant high temperatures occur (3 or 4 days of maximums exceeding perhaps 85o F) which will start the flower bud differentiation process. It is currently still difficult to make precisely timed recommendations, and we cannot guarantee benefits.
If you are interested in applying either urea or phosphorous acid this winter as a test or on substantial acreage, you need to be prepared. The product must be on hand and the spray equipment available on short notice. Low biuret spray grade urea is needed (< 0.5 % biuret on a dry weight basis) or a suitable clean source of buffered phosphorous acid. If you plan to use an aerial applicator, they must use a micronair or similar distribution spray system and they must be booked in advance. This of course complicates timing. Ground sprayers can be used at low volume and fast speeds. Air blast sprayers will work at 50 to 80 gals per acre. Ultra low volume sprayers give good distribution in the outer canopy at 25 to 30 gals/acre. The amount of acreage you can cover will determine your priorities. Healthy trees that had (have) a good current crop should be a higher priority. Weaker trees may benefit, but have less capacity to carry a heavy crop. Navel and other low yielding cultivars (Ambersweet and some Rhode Red strains) that often over-flower, should not be treated to enhance flowering. We have some on-going experiments that suggest that GA3 at the same timing as the urea spray may be useful to reduce excessive flowering on these cultivars and create more mixed inflorescences with good leaf to flower ratios.

FLOWER BUD INDUCTION ADVISORY #2 for 2000-2001-12/13/00

This is an early update to the first advisory because of the warm spell that has occurred this week. Lake Alfred, Immokalee and Tavares have experience 3 to 4 days above 80 degrees F while Ft. Pierce only one. There are an additional 3 to 6 days above 80 degrees predicted on the 8 day forecast.
As of 12/10/00 and based on FAWN data from October 1st, Ft. Pierce, Immokalee, Lake Alfred, and Tavares had accumulated 696, 735, 866 and 883 hours below 70 degrees F, respectively. This is sufficient that some buds are induced and the warm spell will have started them to differentiate if sufficient soil moisture is present. Some bud swell has been seen in Polk County this week.
Growers that managed to maintain a moderate water stress should have suppressed this first flower bud differentiation and will continue the induction process on these as well as other buds on the tree from the water stress and from the next cool weather period. We still want to get to Christmas or early January before stimulating differentiation by applying a flower bud enhancing spray such as urea and increasing irrigation rate.
Many growers have been reluctant to reduce irrigation due to small fruit size and the hope of increasing size by more frequent irrigation. By December, there is little likelihood of significantly increasing fruit size. Other people have not reduced irrigation due to fear of water use restrictions the rest of the winter and next spring. Trees that have been well irrigated will now have bud swell and these shoots will be very susceptible to a freeze if one should occur. Only Hamlin oranges are likely to experience significant drop later on from water stress now. Maintaining some drought stress during warm winter periods would appear to have more benefits than disadvantages.
Again, our goal is to accumulate more than 900 hours below 70 degrees without a warm spell stimulating growth of buds before we want to encourage the trees to begin differentiating flower buds.
Current Weather Status In Relationship To Citrus Flower Bud Induction
And Use Of Winter Foliar Sprays To Enhance Flower Bud Induction

FLOWER BUD INDUCTION ADVISORY #3 for 2000-2001-12/18/00

As everyone has noticed today, we have passed through a typical December warm spell and now have a weather prediction from NOAA of temperatures below or near 70 degrees for most locations until Christmas. This should add about 170 hours to the current totals.
As of 12/17/00 and based on FAWN data from October 1st, Ft. Pierce, Immokalee, Lake Alfred, and Tavares had accumulated 734, 796, 888 and 970 hours below 70 degrees F, respectively. For some stations, there appears to be a data gap in October, which may total another 60 or 70 hours below 70 degrees F.
If trees were maintained in drought stress during last weeks warm spell, there will be sufficient flower bud induction by Christmas and urea sprays should increase bloom intensity. Minimum rates should be 25 lbs N as urea per acre (28 lbs is preferred). Such a spray will usually advance bloom date about one week. The best timing should be just before the next predicted warm spell.
The CREC WebSite (www.crec.ifas.ufl.edu) has a weather link, and this link includes the 8 day predictions by state (FL) and locations (see Ft. Myers, W. Palm Beach, Tampa & Orlando to bracket the citrus industry). We are in the process of building an induction monitoring system which will extrapolate these 8-day prediction values to each FAWN weather location in the state, but for now you must do your own evaluation of the four sites available.
If sufficient soil moisture was present last week, some bud swell should be evident this week. The bloom situation is much better if initiation and bud differentiation were avoided last week by maintaining a moderate level of drought stress. But if not, a gibberellin spray (20 oz per acre of 4 % GA) this week may minimize the bloom from this early bud break. The danger from doing this, however, is that there is no guarantee that sufficient cool hours will follow to provide an adequate bloom at a later date. A GA spray could stimulate shoot growth of the swelling buds if another warm spell comes soon. These buds or young shoots would then be much more susceptible to a freeze.
If some bud swell is occurring this week, it will probably take another 300 or 400 hours of cool temperatures to provide a second set of induced buds that can provide a reasonable set of fruit. If that much additional cool temperatures occurs, a urea spray just before the next warm spell may be beneficial, but we don't have much experience to base that possibility on.
Growers that managed to maintain a moderate water stress last week should have suppressed this first flower bud differentiation and can expect the induction process to continue on these as well as other buds on the tree. Both water stress and cool weather periods are building the induction level. Because of the extended warm period last week, it would be desirable to get to mid-January before stimulating differentiation either by applying a flower bud enhancing spray such as urea and/or increasing irrigation rate. If another warm spell comes after Christmas but before mid-January, then trees should be released from drought stress and allowed to begin flower bud initiation and differentiation. It is questionable if a urea spray will have an effect soon after last weeks warm spell.
Again, our goal is to accumulate more than 900 hours below 70 degrees without a warm spell stimulating growth of buds. If we have reached late December or early January, we can then encourage the trees to begin differentiating flower buds by using a urea spray and increasing irrigation just before the warm spell begins. If a prolonged cool spell now occurs, seedless cultivars like navels and Ambersweet may benefit from a 20 oz per acre spray of GA just before the predicted warm growth temperatures.
Trees that did have adequate moisture last week for growth should have at least two flushes of bloom in the spring.

FLOWER BUD INDUCTION ADVISORY #4 for 2000-2001-12/24/00

The progress of Florida citrus trees toward induction of citrus flower buds from cool temperatures was favorable last week. The cool temperature accumulation below 70 degrees F at Lake Alfred through yesterday is now 1224 hours through Saturday 23 December compared to less than 900 hours below 70 degrees F through January 8th two years ago. This exceeds the hours related to the 75 % induction stage for the 94-83 season. Fort Pierce and Immokalee are 252 and 152 cool inductive hours, respectively, behind Lake Alfred. As usual, Tavares has been cooler than Lake Alfred and has about 40 more hours below 70 degrees F through yesterday. These relative positions are fairly normal.
Presently, it is a mid-moderate flower induction year. The forecast of temperatures for the next 8 day indicates that inductive temperatures will continue for at least another week. The WebSite for these temperature predictions (https://crec.ifas.ufl.edu/, then connect to Weather and 8 day forecast for Florida locations near you) should be examined later this week for the temperature predictions for the week of New Year's day. Enhancement sprays should be effective and can be applied by next weekend. The best time will be just before the next warm spell (3 or 4 days with 80+ degree F maximum). There still may be some benefit if sprays are applied the first 2 or 3 days of a warm spell. We of course still have the possibility of a continued cold spell into mid-January or even early February. Since we have had one warm spell to break continuous flower bud induction, it would be better to wait at least another week if cool weather continues.
In summary, induction by cool temperatures is at the mid-moderate level and enhancement sprays may still be beneficial for flower bud induction if applied before the next warm spell in spite of one warm spell having already occurred. We should expect a fairly concentrated or slightly protracted bloom this year if sufficient water stress was maintained in early December's warm spell. For other blocks, two blooms or a protracted bloom should be expected. Foliar nutrition or PFD control sprays during the bloom period may be more difficult to time because of a protracted bloom period in many blocks that had good soil moisture in early December.

FLOWER BUD INDUCTION ADVISORY #5 for 2000-2001-12/29/00

The progress of Florida citrus trees toward induction of citrus flower buds from cool temperatures was favorable this week and will continue next week. The cool temperature accumulation below 70 degrees F at Lake Alfred through yesterday is now 1330 hours through Thursday 28 December compared to less than 900 hours below 70 degrees F through January 8th two years ago. This exceeds the hours related to the 75 % induction stage for the 94-83 season. Fort Pierce and Immokalee have 1042 and 1126 cool inductive hours, respectively, while Tavares has 1376 inductive hours.
Presently, it is a upper-moderate flower induction year, especially considering the predicted cool weather for next week.. The forecast of temperatures for the next 8 days indicates that inductive temperatures will continue with some temperatures being lower than ideal. The WebSite for these temperature predictions ( www.crec.ifas.ufl.edu , then connect to Weather and 8 day forecast for Florida locations near you) should be examined for the Sunday freeze forecast and further temperature predictions for the week after New Year's day. Enhancement sprays should be effective by next week if daytime temperatures warm to above 70 degrees F. Lower temperatures will reduce uptake of the applied chemical. The best spray timing will be just before the next warm spell (3 or 4 days with 80+ degree F maximum). There still may be some benefit if sprays are applied the first 1 or 2 days of a warm spell. Sprays should be delayed until this cold spell is nearly over. In spite of the early December warm spell, we now have enough additional induction conditions to expect to get a fairly good second bloom even if some buds were starting to differentiate from the first warm.
We have now reached an induction level where gibberellin sprays may help reduce flower intensity and improve set of excessive flowering seedless cultivars like navel and Ambersweet. Expected on-year mandarin blocks may also benefit from reduced flower levels by producing fewer flowers with larger ovaries. Look at the gibberellin spray advisory posted on this same page.
In summary, induction by cool temperatures is now in the upper-moderate range and enhancement sprays may be beneficial for flower bud induction, particularly in Valencias, Hamlins and grapefruit, if applied before the next warm spell in spite of one warm spell having already occurred. Daytime temperatures should be near 70 degrees F before sprays are applied to assure good uptake. We should expect a fairly concentrated bloom this year in blocks where sufficient water stress was maintained in early December's warm spell. For other blocks, two blooms or a protracted bloom should be expected. Foliar nutrition or PFD control sprays during the bloom period may be more difficult if a protracted bloom period occurs in blocks that had good soil moisture in early December.
Watch out for Sunday mornings predicted freeze temperatures.

FLOWER BUD INDUCTION ADVISORY #6 for 2000-2001-1/3/01

Welcome to the new Millennium. It is about time to apply Winter sprays for enhancement of flower bud induction. The progress of Florida citrus trees toward induction of citrus flower buds from cool temperatures continued to be favorable this week and will continue most of next week. The cool temperature accumulation below 70 degrees F at Lake Alfred through yesterday is now 1450 hours through Tuesday 2 January, while Fort Pierce and Immokalee have 1162 and 1281 cool inductive hours, respectively, and Tavares had 1496 inductive hours. This is a (lower) upper level of induction temperature accumulation for Florida.
Therefore, it is a good flower induction year, especially considering the predicted cool weather for next week.. The forecast of temperatures for the next 8 days indicates that inductive temperatures will continue with some daytime high temperatures being slightly higher than ideal. The WebSite for these temperature predictions (www.crec.ifas.ufl.edu , then connect to Weather and 8 day forecast for Florida locations near you) should be examined to determine if the cool temperature period will continue into mid-January. Mid-January is a traditional freeze period in years such as this (El Nino-La Nina neutral). Enhancement sprays should be effective by next week since daytime temperatures are predicted to be above 70 degrees F. Lower temperatures will reduce uptake of the applied chemical. Sprays can be delayed or eliminated this year if cool temperatures continue after next weeks slight warming spell. A urea spray next week may have the benefit of stimulating the initiation process, providing a more uniform bloom that can be 5 to 7 days ahead of non-sprayed blocks.
Urea sprays should be at the rate of 25 to 28 lbs N as urea per acre (53 to 60 lbs of urea). If phosphorous acid formulas are used, they should be applied at 2.6 quarts of 26-28 % P product or equivalents per acre.
We have now reached an induction level where gibberellin sprays may help reduce flower intensity and improve set of excessive flowering seedless cultivars like navel and Ambersweet. Expected on-year mandarin blocks may also benefit from reduced flower levels by producing fewer flowers with larger ovaries. Look at the gibberellin spray advisory posted on this same page. Application rates of 20 to 30 grams per acre are recommended.
In summary, induction by cool temperatures is now in the upper range. Enhancement sprays may still be beneficial for flower bud induction, particularly in Valencias, Hamlins and grapefruit. Next weeks temperatures appear favorable for application of sprays. Daytime temperatures should be near 70 degrees F or higher before sprays are applied to insure good uptake. We should expect a fairly concentrated bloom this year in blocks where sufficient water stress was maintained in early December's warm spell. In blocks with moderate water stress in early December and a moderate crop this year, bloom may be adequate without an enhancement spray. For other blocks, two blooms or a protracted bloom should be expected. Boosting the flower induction of the second bloom and advancing its date of bloom may be beneficial.

FLOWER BUD INDUCTION ADVISORY #7 for 2000-2001-1/10/01

Currently, we are at the highest level of winter cool temperature accumulation for flower bud induction compared to 20 years of data that has been analyzed. The warming spell expected this weekend and early next week will likely trigger the initiation of differentiation of flower buds. As discussed earlier, this will be the second set of initiated flower buds for many trees. The first set of flower buds started initiation in early December with the warm spell of December 7 to 9. One of the unknowns in this year's flower bud induction temperature accumulation is ‘How much does that first warm spell diminish the total effect on flowering?'. We have not experienced a comparable winter since we started this work on flower bud induction. We expect that most blocks of citrus will not need help from a winter urea spray in order to have good flowering. However, successful use of winter urea has been reported from California even though they accumulate many more hours of cool temperatures than occurs in Florida.
Another unknown this year is the possible effect of slight freeze injury in many blocks that has led to leaf but not wood injury with subsequent losses of 50 to 80 % of the leaves. There may be a slight stress effect associated with this level of injury which could enhance flowering, make it more synchronized and possibly advance the date of bloom.
Of the years that we have studied, it may be least likely this year that urea sprays will enhance flowering or that enhanced flowering is needed. The most likely trees to benefit from a winter urea spray applied now are Valencia trees with a good current crop that had good soil moisture in early December when the warm spell could cause induced flower buds to initiate growth. There have been only about 850 hours of cool temperatures accumulated since that warm spell. This is less than the 900 which normally relates to a good urea spray response. However, we do not know how much flowering response we will get in the second set of flower buds from this intense level of induction.
Trees that are more likely to benefit this year from adjustment of flowering levels are seedless cultivars that flower excessively almost every year (see the last advisory). These cultivars will likely benefit from a gibberellin spray (see gibberellin advisory on this page). The timing of these sprays should be later next week or early the following week. If a urea spray is to be applied it should be put on from tomorrow (Thursday) through the first day or two of next week.

FLOWER BUD INDUCTION ADVISORY #1 for 1999-2000-12/3/99

The 1999-2000 Fall-Winter weather in Florida is expected to be influenced by a continuing La Nina event that affected Florida weather last Winter. Meteorologists predict that, overall, warmer and dryer than normal weather will occur in Florida, but that also means the chances of a freeze are increased. Warm average conditions suggest that inadequate cool temperatures for induction of citrus flower buds is likely. A prolonged period of cool temperatures (below 75 o F) with no tree growth is necessary for good flower bud induction to occur. Warm periods can initiate bud differentiation (growth) and discontinue the induction process. Last winter season at least four cool periods were followed by week-long warm periods. This led to the observed 4 blooms that occurred from January through late April to early May. Since a single prolonged cool period is less likely this year, methods to increase citrus flower bud induction may be useful.
The other natural process for flower bud induction in citrus is by drought stress sufficient to stop tree growth and cause induction to proceed. Drought stress is the primary process of flower bud induction of citrus in low land tropical climates. In some years, drought stress is operative under Florida winter conditions and also can be responsible for ‘June blooms'. If little rain occurs during a warm winter (more likely in this La Nina year), significant drought stress may develop without irrigation. Of course, if significant rain occurs drought stress will be diminished or not occur. Withholding irrigation for at least 30 to 40 days should be long enough to increase flower induction. Drought stress also can stop initiation of differentiation of potential flower buds if intermittent warm periods occur during the winter. Some growers avoided multiple blooms last year by keeping their trees drought stressed until they were ready to initiate flower bud differentiation in mid-January.
In spite of the general prediction for relatively warmer temperatures this year, the Fall has been cool and excellent induction temperatures are occurring in the 1st week of December. Through November 30th nearly 200 more hours below 700 F have accumulated than last year. This helps to stop growth and get the flower bud induction process underway. As IFAS did last year, the FAWN (Florida Agric. Weather Network) WebSite will provide additional information on accumulated hours of cool temperatures. The hours of temperatures below different thresholds can be viewed for each of 15 available sites by going to FAWN (linked through http://www.crec.ifas.ufl.edu) and to option 4 (select data).. In the four fields, choose the location, summary data and specify the dates to be included, then click on search. This will provide a summary of hours accumulated below different temperatures between the specified dates. You should choose October 15th or November 1st as your starting date. I will attempt to relate the cool temperature accumulation and warming spells to previous good and poor flower induction years as this winter progresses. Weekly advisory reports will continue until mid or late January, after which it is less likely that any attempts to alter flower bud induction will succeed. Since 7 to 10 day temperature and rainfall forecasts are available, we can anticipate when a given cool period will end. We will discuss more on the use of this information later.
Moderate drought stress may be maintained on flatwood bedded groves with the irrigation system shut down. By maintaining the water table just below the bottom of the water furrows, daily stress can occur with some recovery each night from moisture taken up by the tree roots that extend to near the bottom of the water furrow. If the water table is one or more feet below the water furrow, severe drought stress will occur if irrigating is stopped and their is no rain. Also, if severe root pruning occurred due to high water levels during the previous two years, then a water table at the bottom of the furrow may still result in a severe stress level. Visual observation of temporary leaf wilting can be a good indicator of proper stress. Wilting by 10 or 11 am and recovery over-night is ideal. Drought stress is much more difficult to develop on deep sandy soils due to the deeper rooting zone. Two or three weeks may be required on deep sands in order to reach an adequate level of stress to begin flower bud induction. Drought stress can be used on Valencia trees, trees already harvested or Hamlin trees that will be harvested during December. Trees with fruit intended for fresh market should not be subjected to severe drought stress. Valencias hold their fruit very tightly, but Hamlins for later harvest or Pineapple oranges are likely to experience excessive drop of the current crop if subjected to even moderate drought stress.
If one or more winter-time rain fronts negate the attempt to maintain water stress, the associated cool weather behind the front (a typical occurrence) may provide some cool temperature induction. The issue will be whether enough induction has occurred. Even in cool years of good induction conditions, winter sprays of stress-boosting chemicals can provide benefits by increasing flower bud induction and subsequently yields of at least Valencia trees on flatwood soils. Four years of tests on Valencia oranges on bedded grove sites have shown a consistent enhancement of total yield and pounds solids per acre from urea or potassium phosphite (PO3) sprays (Albrigo, Proceedings Florida State Hort. Soc., 1999, in press). Some grower tests using these materials have provided similar increased flowering and yield results on other cultivars as well as Valencia trees.
After some cool temperature induction or 30 days of drought stress, foliar sprays of either 50 to 60 lbs of spray grade urea per acre or 2.6 quarts of 28 % P as potassium phosphite per acre can enhance flower bud induction. Foliar sprays of urea or phosphorous acid products presumably work only if some induction has taken place from natural cold or drought stress. Lovatt, et al.(1988) demonstrated this for foliar sprays of low biuret urea. In our previous tests, the timing of this spray was between Christmas and January 5th. In years of strong El Nino or La Nina events, suitable timing may be earlier or later. In any case, the timing must be before significant high temperatures occur (3 or 4 days of maximums exceeding perhaps 85o F) which will start the flower bud differentiation process. It is currently still difficult to make precisely-timed recommendations, and we can not guarantee benefits. None-the-less, advisories on the accumulation of cool temperatures, generated from the FAWN weather system, and recommended spray timing for Winter sprays will appear on the Citrus Research and Education Center Web Page each Tuesday morning starting the week of December 13th. This website is at http://www.crec.ifas.ufl.edu (look under Grower Aids). This information will be forwarded to County Extension offices and other publishing sources. It should be noted that waiting for these written announcements may cause delays in management practices which may result in missing an important timing window.
If you are interested in applying either urea or phosphorous acid this winter as a test or on substantial acreage, you need to be prepared. The product must be on hand and the spray equipment available on short notice. Low biuret spray grade urea is needed (< 0.5 % biuret on a dry weight basis) or a suitable clean source of buffered phosphorous acid. If you plan to use an aerial applicator, they must use a micronair or similar distribution spray system and they must be booked in advance. This of course complicates timing. Ground sprayers can be used at low volume and fast speeds. Air blast sprayers will work at 50 to 80 gals per acre. Ultra low volume sprayers give good distribution in the outer canopy at 25 to 30 gals/acre. The amount of acreage you can cover will determine your priorities. Healthy trees that had (have) a good current crop should be a higher priority. Weaker trees may benefit, but have less capacity to carry a heavy crop. Navel and other low yielding cultivars (Ambersweet and some Rhode Red strains), that often over-flower, should not be treated to enhance flowering. We have some on-going experiments that suggest that GA3 at the same timing as the urea spray may be useful to reduce excessive flowering on these cultivars and create more mixed inflorescences with good leaf to flower ratios. We will report on these results in a later advisory. Look for our first weather advisory on December 14th.

FLOWER BUD INDUCTION ADVISORY #2 for 1999-2000-12/14/99

Please refer to the first advisory of this year (12-6-99) for general background information of factors affecting flower bud induction. So far this Fall-Winter, there has been better cool temperature induction of citrus flower buds than last year. For Lake Alfred through Sunday, there were 1100 hours below 75o F compared to less than 900 hours below 75o F last year to 12-12-98. This, however, is still more than 200 hours short of the cool temperature accumulation by 7 January last year when urea foliar sprays enhanced flower bud induction. At the current rate of cool temperature accumulation, it will take another 2 weeks to reach the level on January 7th last year. The National Weather Service (NWS) predicts that cooler weather is likely during the next 2 or 3 days and then highs again in the high 70s are expected for the remainder of the 8 day forecast. These predictions can be seen on their WebSite . Again like last year, we probably will be short of the 2800 hours below 75o F that occurred in the 94-83 season by the time 100 % of flower bud induction (FBI) had occurred. Based on summary data from FAWN weather stations, Lake Alfred has accumulated about 100 to 200 hour more inductive cool temperatures so far this year compared to Ft. Pierce or Immokalee. This is probably typical of the difference between South and Central Florida in most years.
An advantage in the accumulation of flower bud induction temperatures this year over last year is that, so far, no intervening week of temperatures above 85oF has occurred. These high temperature events occurred four times last year and resulted in 4 separate blooms. We do not know, however, if the temperatures of near 80oF maximum each day with a low of 60oF last week will trigger some flower bud differentiation. Some water stress during this period would have kept the trees in sufficient rest to prevent any flower bud growth. On flatwood soils, 3 or 4 days of withholding water without rain would create such a stress. On the induction side of the temperature responses, we also do not know yet if temperatures from 75o F to 70o F are as good as those below 70o F for induction, we suspect that they are not as good. Studies of specific value of different temperatures for induction are still underway.
If currently predicted or cooler temperatures persist for two more weeks (until Christmas), chilling accumulation would be about equal to last year at the end of the first week of January. That timing would have more probability for a response from enhancement sprays for flower bud induction. The current predicted spray timing is Christmas to New Year. If the current cool temperatures are not sufficient to stop flower bud differentiation from starting, bud swell (separation of the bud scales) will appear, can be observed and sprays would be too late. If the current temperatures are coupled with some water stress, the trees should remain dormant and allow some additional natural stress induction to occur before the preferred time for foliar sprays of urea or buffered phosphorous acid to enhance flower bud induction. However, any period with warmer than 85oF highs will assuredly start flower bud differentiation if there is no water stress to counteract the hot period.
Flower bud induction (FBI) sprays need to be applied no later than the beginning of a hot spell (defined as 85oF or higher daytime maxima). The current moderate cool period is predicted to last more than this week according to the NWS. If so, spraying should be scheduled just before the next predicted period of daytime highs in the mid to high 80s that is likely to last more than 2 or 3 days. These are best guesses only. Unfortunately, we do not have sufficient data to predict more accurately either our exact FBI status nor just how much warm temperature will start the differentiation process. Last year, every 5 to 7 day period of daytime highs in the mid to high 80s started the differentiation process of all buds with sufficient induction and more buds were promoted through induction with each additional cool period. Once the differentiation process is sufficiently started, a foliar spray cannot alter the determination of a buds status as vegetative or flowering. Based on last year, it appears that the foliar sprays were still effective as much as 2 to 3 days into a hot period.
Based on some higher than recommended spray rates used last year, it is even more likely than previously believed that the action of either urea or phosphorous acid at winter time is by enhancing stress induction of flower buds. The urea action may be by the phytotoxicity of the urea itself and the rapid release of ammonia in the plant tissues. Various forms of PO3 can be phytotoxic at high enough rates. The recommended rates of both are just below the threshold to cause tissue necrosis. The urea should be low in biuret because leaf tissues do not recover from biuret toxicity and remain yellow. Suppliers should provide a written analysis of biuret content (less than 0.5 % on a dry spray grade basis). Forms of PO3 should be free of heavy metals or other contaminates. Good sources of PO3 are essentially clear liquids, but an analysis of trace elements should be provided.
For urea, remember that the recommended rate is 25 to 28 lbs of N as urea/ac or 53 to 60 lbs of urea/acre. Six bags of urea (300 lbs) per 500 gal tank sprayed at 100 gal/ac is a simple guide. If you calibrate a speed sprayer to deliver 60 or 80 gal/ac, an acceptable volume to get good outer canopy coverage and maximize sprayer use, then 10 bags or 7.5 bags of urea per tank, respectively, will give the 60 lbs of urea/ac rate. In our previous studies with phosphorous acid, we used 2.6 quarts of an 0-28-26 liquid product. The current label of some products may be for 2 quarts per acre and by law is the limit you can apply.
At this time, it appears that any foliar sprays should be scheduled for 2 weeks from now or slightly later if cooler temperatures were to develop and persist. If trees are drought stressed before the next hot weather returns with no irrigation or intervening rainfall, an additional week or two of induction may be possible before sprays are applied. Severe water stress should not be allowed if the trees have a current crop, and the crop is intended for fresh market. Next weeks advisory will update temperature distributions, expected weather for the following 8 days, and a firmer recommendation for the timing window for winter sprays to enhance flower bud induction.

FLOWER BUD INDUCTION ADVISORY #3 for 1999-2000-12/20/99

Please refer to the first advisory of the year (12-6-99) for general background information of factors affecting flower bud induction. I have made 2 corrections in the earlier information. This is a La Nina Winter, but in one sentence it was written as El Nina. The other correction was on the formula of the phosphorous acid product used as a foliar spray. In later test, a 0-28-26 formula was used at 2.6 qts/ acre not a 30% P product. The earlier tests were with an 0-40-0 product at 2 qts/ac that was buffered with KOH on-site.
This weeks report might be titled ‘The Good, The Bad and The Ugly'. The good is that temperatures have continued to stay in the upper part of the effective induction temperature range. This is much better than the frequent jumps into the high 80s that occurred last year. Further good is that the 8 day forecast has some cooler days expected starting Wednesday. The bad is that the general rains (1 to 2.5 to inches, except none reported on FAWN for the Immokalee Center) eliminated any water stress that growers may have initiated during the last two weeks. This is not too bad since as expected, the rains are being followed by some cooler temperatures. The ugly part is that the extra hours of induction temperatures accumulated so far this winter are in the upper range of effective temperatures for flower bud induction. We don't know yet how effective this range of temperatures is. The total numbers, however, are becoming favorable.
For Lake Alfred through Sunday, there were 1258 hours below 75o F compared to 1058 hours below 75o F last year to 12-19-98. The below 70o F hours are only about 100 hours short of the cool temperature accumulation by 7 January last year when urea foliar sprays enhanced flower bud induction. At the current rate of cool temperature accumulation, it will take another week to reach the level on January 7th last year. The National Weather Service (NWS) predicts that cooler weather is likely after the next 2 days and should continue for the remainder of the 8 day forecast. These predictions can be seen on their WebSite (put link to Website here, thank you very much). Based on summary data from FAWN weather stations, all citrus locations are still about 200 accumulated cool hours ahead of last year. The expected window for a foliar spray of urea or phosphorous acid to enhance flower bud induction is anytime after next weekend until a warm front of several days in the 80s occurs.
Urea just prior to such a warm front can stimulate the start of differentiation and lead to an earlier bloom. The possibility of a January freeze should be considered in planning. If no warm spell occurs through the first week of January, it is advisable to wait until the second week of January to spray in order to minimize the start of differentiation and the associated loss of cold hardiness. On-the-other hand, the marginally cool temperatures so far this winter indicate that winter spray to enhance flower bud induction is likely to be beneficial in most cultivars except heavy blooming ones like navels and Ambersweet. The decision as to whether to spray or not will be difficult if a warming spell appears before the 1st week of January ends. After that, the stimulation of growth by a late winter spray (1st or 2nd week of January) will be after the most likely period for a hard freeze.
For those planning to use gibberellic acid on navels or Ambersweet, it is not yet legal to apply GA after December 31st. Therefore, sprays should be applied before January. We have posted a new information sheet prepared by Dr. Ed Stover and myself on this site (see under Grower Aids).. This is an update of our work with GA on these cultivars and the preliminary recommendations we can make at this time.
If currently predicted cooler temperatures persist for this week (until Christmas), chilling accumulation would be about equal to last year at the end of the first week of January. That timing would have good probability for a response from enhancement sprays for flower bud induction. The current predicted spray timing is Christmas to New Year or later if cool weather persists.. Any bud swell (separation of the bud scales) that has been observed will probably stay at that stage during the cool temperatures this week. The additional natural stress induction expected to occur this week and at least part of next week should increase the likelihood for foliar sprays of urea or buffered phosphorous acid to enhance flower bud induction. However, any period with warmer than 85oF highs will assuredly start flower bud differentiation as there is no water stress to counteract a hot period.
For urea, remember that the recommended rate is 25 to 28 lbs of N as urea/ac or 53 to 60 lbs of urea/acre. Six bags of urea (300 lbs) per 500 gal tank sprayed at 100 gal/ac is a simple guide. If you calibrate a speed sprayer to deliver 60 or 80 gal/ac, an acceptable volume to get good outer canopy coverage and maximize sprayer use, then 10 bags or 7.5 bags of urea per tank, respectively, will give the 60 lbs of urea/ac rate. In our previous studies with phosphorous acid, we used 2.6 quarts of an 0-28-26 liquid product. The current label of some products may be for 2 quarts per acre and by law is the limit you can apply.
At this time, it appears that any foliar sprays should be scheduled for next week or slightly later if cooler temperatures were to persist. If trees again become drought stressed before the next hot weather returns, with no irrigation or additional intervening rainfall, another two weeks of induction may be possible before sprays are applied. Severe water stress should not be allowed if the trees have a current crop, and the crop is intended for fresh market. Next weeks advisory will update temperature distributions, weather predictions for the following 8 days, and expectations for closing the timing window for winter sprays to enhance flower bud induction.
Enhancing Cropping of Low-Yielding, Heavily Flowering Citrus by Reducing Floral Initiation
Ed Stover, Citrus Extension Specialist, Indian River Research & Education Center
Gene Albrigo, Research Scientist, Citrus Research & Education Center
Many Florida blocks of Navel orange, Ambersweet, and Minneola tend to flower very heavily yet set poor crops. It appears that tree resources are wasted by extravagant flowering, compromising the trees' ability to set fruit, support early fruit growth, and carry fruit to harvest. Research in several citrus areas indicates that productivity of heavily blooming blocks may be increased by reducing flower formation. This approach has produced very encouraging results in Florida Navel and Ambersweet in two years of trials. While we don't have sufficient information to make strong recommendations, results have been so positive, that some citrus growers may want to try these methods on low-yielding but heavily-flowering groves on a limited scale. The purpose of this article is to provide an update for citrus growers on this promising technique.
A single winter GA spray to Ambersweet or Navel has increased boxes/tree by more than 22% in our trials.
How does this work?
GA (also known as GA3 or gibberellic acid) is a naturally occurring plant growth regulator that has a number of effects on tree and fruit development. GA is known to inhibit flowering in citrus, and when it is applied during the period of bloom induction, it typically reduces the number of flowers and increases the proportion of leafy inflorescences.
When should GA be applied to reduce flowering?
The period of flower bud induction in Florida citrus typically occurs from late November through mid-January in Florida. In 1997-98, we applied GA to Navel in Ft. Pierce on Dec 23, 1997 and Ambersweet in Okeechobee County on Jan 6, 1998. Flowering was reduced by about 40% in each trial and total yield was increased by 22% in Navel and 45% in Ambersweet. We have only looked at a range of GA timings for one year, and found that in that year, time of GA application markedly influenced both time of flowering and final crop harvested. Application of GA to Ambersweet on Jan 6, 1999 reduced and delayed flowering but had little effect on yield, however, application on January 23 accelerated flowering and greatly increased cropping, from a very poor 25 fruit / tree in controls to 275 fruit / tree. In Navel, yield increased following application on Dec 17, 1998 (42% increase) and Jan 6, 1999 (25% increase). Nov 23, 1998 and Jan 25, 1999 treatments to Navel reduced flowering and altered time of bloom but had no effect on yield. It appears that optimum time of GA treatment will likely depend on variety and time of cool temperature periods that induce flowering. Weekly advisories on flower bud induction status, and the best time to apply sprays that alter flower bud induction are posted on the web at http://www.crec.ifas.ufl.edu/crechome/groweraids.shtml. Best results may be achieved by following the 1999-2000 flower induction advisory on this website. For 1999-2000GA spray timing, we expect that a Christmas to January 5th window will be acceptable. Trials are beginning in Minneola, and we suspect that this late-blooming variety may need to be treated with GA about one week later than the earlier blooming Navel and Ambersweet.
Because of recent temperatures, our best guess is that Ambersweet should be treated with GA in early January 2000, while Navel should be treated in late December 1999. See website.
Where can GA be legally used to reduce flowering?
The current ProGIBB label permits application to Navel during December to reduce physiological disorders and permit a more orderly harvesting pattern. Therefore, application to reduce the physiological disorder of excessive flowering is permitted by the existing label. HOWEVER, THE EXISTING LABEL DOES NOT PERMIT ANY APPLICATION OF GA TO CITRUS IN JANUARY. The makers of ProGIBB are working with us to get special local needs labeling for this use and we will alert you when this is received. A full label for controlling flowering in citrus should be in place for 2001.
The existing label does not permit GA application to citrus in January. A special local needs exemption may be in place for January 2000. Please call your citrus agent for an update before any January GA sprays.
Where should you consider using GA to reduce flowering?
THIS IS STILL AN EXPERIMENTAL PROCEDURE! However, it is worth trying on limited acreage where trees routinely flower very heavily but produce very light crops. We have only tested this procedure on Navel and Ambersweet, but it seems likely to be effective on other bouquet bloomers as well. Trials on more varieties will be conducted in 1999-2000. Because treatments sometimes result in earlier flushing, there is a chance that winter GA may reduce cold-hardiness and we are also testing this possibility. If there are still fruit on the tree at application, you may experience undesirable regreening.
What rate should you use?
All of our trials have been conducted with 20 ounces of ProGIBB (4%) per acre applied at 125-175 gallons per acre with 0.05% Silwet L-77. Lower rates, gallons per acre and surfactants may be effective but we have not tested them. Lower rates of GA per acre will be tested in 1999-2000.
At 150 gallons/acre, this would be : 13.3 ounces of GA (4%) and 6.3 ounces of Silwet L-77 per 100 gallons
What will happen following winter GA application?
Some leaves may be knocked off of trees, especially where greasy spot has damaged foliage or temperatures are high at the time of application, however we have seen increased cropping even after some leaf loss. Fruit still present on trees may quickly and dramatically regreen. Bloom is likely to be reduced, will be associated with more leafy flush, and may be earlier or later and more concentrated than in untreated trees. In our experiments, final crop has been markedly increased by most treatments.
Please tell your citrus agent what you see following GA treatments to reduce flowering and enhance cropping. Your information will help us develop stronger recommendations more quickly.

FLOWER BUD INDUCTION ADVISORY #4 for 1999-2000-12/27/99

A best guess is that urea or phosphorous acid sprays can be applied starting this week for enhancement of flower bud induction. Thursday or later this week may have the advantage of higher temperatures to increase foliar uptake of the spray material. From a cool temperature accumulations status, this timing is essentially equivalent to last year through the first week of January when sprays were effective. Relative to last year's temperature profile, this year is better because no intervening hot (+ 85 degree F) periods have occurred, but this year, the additional cool temperatures have been in the 65 to 75 degree range, the upper range of temperatures thought to be inductive. So far this Fall-Winter, cool temperature accumulation for induction of citrus flower buds continues to be relatively low. Through Sunday, hours below 70 degrees F were between 900 and 1100 hours in the Central to South citrus districts, while hours below 75 degrees were between 1280 and 1410 hours. To the North, an additional 50 to 60 hours had accumulated below these temperature values. Since the cool temperature induction has been only moderate, flower bud induction is likely to benefit from stress enhancing sprays.
The current week has been of ideal temperatures for flower bud induction but not many hours below 60 degrees F occurred prior to that. The weather prediction for Thursday through Monday (December 30th - January 3rd) is for 78 -80 degree F highs. It is most likely that citrus trees will start flower bud differentiation of induced flower buds as soon as a period of 4 or 5 days with daytime temperatures in the 80s occurs. We do not know if the upcoming weekend with daytime highs of 80 degrees will trigger flower bud differentiation. January in this La Nina year is predicted to be above normal. Flower bud differentiation will start early in the month if the 80 degree weather continues. Sprays should be applied before an extended warm period begins.
In our tests last year, urea was effective in enhancing induction of flower buds at a equivalent accumulation of inductive temperatures. For this foliar spray treatment to be effective, it will need be applied before significant flower bud differentiation begins. The appropriate treatment window would be this week or later as long as a warm period does not occur. The 8 day temperature forecast looks favorable through Tuesday of next week. If daytime highs remain near or below 80 degrees F next week, sprays may still be effective based on last year's test results.
If you have re-established water stress after last week's rainy cold front, your trees can be held another 2 weeks until after the second week of January before spraying to enhance flower buds. Irrigation should then be resumed. This delay should help to avoid the stimulation of growth before the most likely freeze danger period has passed.
Several cultivars may benefit from reducing flowers, increasing leafy bloom and thereby getting higher fruit set. For navels, Ambersweet and other heavy flowering but low setting cultivars, application of GA sprays should be considered this week. See the accompanying extension advisory for further information on the use and benefits of GA sprays, but note that the legal window for application is only until January 1st.
In summary of the current status of flowering potential in Florida citrus, flower induction is probably low to moderate, but better than last year based on fairly continuous cool temperature accumulation. Foliar sprays of urea or phosphorous acid to enhance flower bud induction are likely to work if applied this week or early next week. If you have established water stress after last weeks cold front, the stress should be continued for one or two more weeks. Irrigation should then follow any enhancement spray. For heavy blooming cultivars, a GA application is appropriate late this week. These various procedures should provide a reasonable level of bloom within the normal bloom period. Currently, it appears that we should have a single bloom with only a slight chance that it will be prolonged due to a previous period when daytime highs were in the low 80s. People that had their trees water stressed at that time should not experience a prolonged bloom.
Further delay before using a flower induction enhancing spray may be beneficial due to additional accumulation of cool temperatures. But that delay increases the risk of shortening the period for effective spraying if warm weather continues next week or a warmer period occurs in the next 2 weeks. Delaying also increases the chance of a prolonged bloom and decreases the chance of stimulating an earlier bloom for fresh market cultivars.
For those that hold out another week, we will briefly update flower bud induction conditions next week. Further advisories will occur if there are unexpected climatic events in January. One advisory on bloom-time options for fruit set will be posted later.

FLOWER BUD INDUCTION ADVISORY #5 for 1999-2000-1/3/00

The progress of Florida citrus trees toward induction of citrus flower buds from cool temperatures was favorable early last week, but warmer days last weekend and continuing today and tomorrow may start flower bud differentiation. This is particularly true for South Florida and East Coast locations were low 80 degree F highs are expected throughout the week. If you have not applied a flower bud enhancing spray of urea or phosphorous acid and you planned to, the earlier this week you do so the better.
The cool temperature accumulation below 70 degrees F at Lake Alfred through yesterday is now 200 hours more than through Saturday 8 January of last year which was 875 hours below 70 degrees F and 1125 hours below 75 degrees F. This exceeds the hours related to the 75 % induction stage for the 94-83 season. Fort Pierce and Immokalee are 160 to 175 cool inductive hours, respectively, ahead of last year also. As usual, Tavares has been cooler than Lake Alfred and has about 50 more hours below 70 degrees F through yesterday.
It would appear that it is still likely to be a moderate to low flower induction year, unless the temperature range from 65 to 75 degrees F is more effective than anticipated. Enhancement sprays should be effective and should have been applied by last weekend. There still may be some benefit if sprays are applied in the next 2 or 3 days. Delays beyond that are not advised as earlier studies in Gainesville showed that flower bud differentiation started, even that far North, by January 15 to 20. We of course still have the possibility of another cold spell in mid-January to early February, which could lead to a second set of induced buds. If flower bud induction sprays were applied last week or early this week, it is less likely that a significant second bloom will occur even if another cool spell occurs.
In summary, induction by cool temperatures is on the moderate side and enhancement sprays may still be beneficial for flower bud induction if applied early this week. We should expect a fairly concentrated or slightly protracted bloom this year. Foliar nutrition or PFD control sprays during the bloom period should be easier to time because of a less protracted bloom period than last year.
This will be the final advisory for this Winter, unless another significant cold spell occurs. I hope they have proved useful and my best guesses are not too far wrong. I would appreciate email responses this Spring as to your observations of bloom intensity and spread, your enhancement sprays experiences, and if applied, did they appeared to help you bloom situation. My email is albrigo@crec.ifas.ufl.edu I will post an advisory closer to bloom time as to final assessment of bloom time and intensity and foliar nutritional options you may wish to consider.

FLOWER BUD INDUCTION ADVISORY #6 for 1999-2000-1/24/00

Significant advancement of flower bud induction is occurring in mid- to late January following an earlier warm spell. Over 1400 hours below 70 degrees F have occurred in South Florida (Immokalee and Ft. Pierce) and over 1650 in the Central and Northern districts. An additional 100 or more hours of inductive temperatures can be anticipated before a warm period starts on next Saturday. At the very least, we can now expect a prolonged bloom period or 2 separate blooms if the previous warm periods of low 80 degree temperatures initiated significant differentiation. Overall bloom should now be heavy, particularly in all blocks that had a light crop this current year.
It is very important at bloom-time to observe blocks treated in late December or early January with urea or PO3 to enhance bloom or GA3 to reduce bloom to see if they have a more concentrated, earlier bloom than comparable untreated trees. We have initiated urea and GA3 timing experiments to see what effect timings throughout January have on flowering distribution and intensity. We will report on those findings before the next bloom induction cycle. Any observations from growers about their experiences this year will be greatly appreciated.
Although a spray of urea this week will likely increase flower bud induction from the later January period of cool temperatures, the result may be an increased second bloom. For early market cultivars, this may not be an advantage. For processing oranges, flowering from this induction period should still result in a bloom during the normal span of bloom (late February to early April) and the resulting fruit should have satisfactory maturation, but a prolonged or heavy second bloom will increase the diverse maturation status of fruit on the tree and result in a poorer average fruit quality from a single harvest.
If the projected warm period starting next Saturday is extensive, bloom should come quickly. We will post an advisory regarding expected bloom date after February 5th.

FLOWER BUD INDUCTION ADVISORY #6 for 1999-2000-2/11/00

The evidence from Florida citrus trees is that we will likely have two blooms on most trees. I know you didn't want to hear that, but it is my best guess at this point. After the more than 1075 hours below 70 degrees F accumulated at Lake Alfred through January 2nd, we experienced 10 days in which temperature maxima exceeded 80 degree F. This amounted to 168 hours above 75 degrees F over a 13 day period. At the time we speculated about whether these temperatures were high enough to start and push flower bud differentiation along far enough to give us a separate bloom. As most trees are pushing buds to varying stages now, even though we have had cool weather, it is obvious that a significant bud break was initiated.

Since then more than 450 to 500 hours below 70 degrees F have been accumulated in the various citrus districts. This should cause more buds to be induced into flower buds. This cool period has lasted 26 days. A normal bloom lasts about 4 weeks. It would appear that little overlap of a second bloom with the first is likely as the first bloom had 2 weeks of warm temperature differentiation plus 3 ½ weeks of cool temperature development.
Growers who continued water stress through the 2 weeks of warm temperatures in early January may have prevented the differentiation that started the 2nd or 3rd of January. Other growers that used a urea or phosphorous acid (PO3) spray at that time may have enhanced the induced flower bud level so that a significant 2nd bloom will not be seen. Everyone involved in these programs should observe their trees carefully. Please report your observations as to bloom intensity and occurrence of any second bloom.

Using a rough model for differentiation and bloom development relative to temperatures, about 70 % of the process may have occurred in the most advance cultivars. Another two weeks of daytime highs averaging over 80 degrees F should put these cultivars at 50 % full bloom from the first wave of flower bud differentiation. This would be about February 26th to March 1st. The second wave should be about 25 to 30 days later assuming average daytime highs are 80 degrees. Watch for a second, April 1st, bloom, no fooling.That is enough guess work. When bloom does come, those with hybrids that require cross-pollination may find a new article useful. This article deals with bee preference within citrus cultivars and some advise on how to maximize efficiency of pollination for your target hybrid cultivars. A short popular version will be posted on this WebSite also under Grower Aids by early next week. The work was supported by the Florida Citrus Production Research Marketing Order.
Please report full bloom dates by email to help us with our predictive model. Also please report your observations on effects of drought stress and/or flower enhancement sprays.

FLOWER BUD INDUCTION ADVISORY #1 for 1998-1999-12/15/98

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS
The following information has been developed as part of the Decision Information System for Citrus.
L. Gene Albrigo, Horticulturist Emeritus
Citrus Research & Education Center, Lake Alfred, FL

So far this Fall-Winter, there has been very little cool temperature induction of citrus flower buds. Between the various citrus growing districts, there is probably very little difference in cool temperatures accumulated so far this year since daytime temperatures have been in the 80s. We are not close to 2 previous seasons (93-94 and 94-83) in which 1300 to 2800 hours below 75 degrees F, respectively, had occurred by the time 100 % of flower bud induction (FBI) had occurred. For Lake Alfred through Saturday, there was less than 600 hours below 75degrees F and even fewer hours in the more desirable range between 40 and 70 degrees F. Most induction to this point has probably been due to water stress. Even with micro sprinklers operated twice a week, growers are reporting daily wilting. The period of water stress induction may still be operative if your Sunday rainfall was less than 1/4 inch as reported for most FAWN stations in the major citrus areas. It would require more than ½ inch to have provided any stress release.

In two previous seasons, we have collected data on the amount of FBI as the Fall and Winter progressed. Insufficient data is available to develop a working model, but we can look at general trends as some aid in estimating our current status. The current cool weather accumulation this Fall-Winter is equal to that at which about 25 % of the maximum bloom induction occurred in 93-94 and 94-83, taking into consideration the least number of hours associated with 25 % bloom in those years. If the NOAA predictions are correct for this coming week, most of the temperatures should be in the effective FBI range. Even so, we will still have less hours of low temperatures accumulated than related to 50 % FBI in the 2 years of records. A second week of similar temperatures would bring us to about the 50 % level according to those previous years. If cool temperatures persist until then, we would be into the week after Christmas and have more probability of a response from foliar induction enhancement sprays. As long as cool temperatures continue, the trees should remain dormant and little bud differentiation is likely considering the low amount of inductive temperatures so far. However, any warm spell is likely to start flower bud differentiation. Of course many blocks of early cultivars like navels have flush and some bloom already. Two or three weeks of cool weather will bring on induction of a second bloom that may be small due to loss of potential buds to these Fall flushes.

FBI sprays need to be applied no later than the very beginning of a warm spell. This cool spell hopefully will last more than this week, spraying should be scheduled just before the next NOAA predicted warm spell of daytime highs in the high 70s or low 80s for 3 to 4 days. These are best guesses only. Unfortunately, we do not have sufficient data to predict more accurately either our exact FBI status nor just how much warm temperature will start the differentiation process. Once the differentiation process starts, a foliar spray cannot alter the determination of a buds status as vegetative or flowering.

It is likely that the action of either urea or phosphorous acid at this time is by enhancing stress induction of flower buds. The urea action may be by the rapid release of ammonia in the plant tissues, while PO3 in its various forms can be phytotoxic at high enough rates. The recommended rates of both are just below the threshold to cause tissue necrosis. The urea used should be low in biuret (less than 0.5 %) because leaf tissues do not recover from biuret toxicity and remain yellow. Suppliers should provide a written analysis of biuret content. Forms of PO3should be free of heavy metals or other contaminates. Good sources are essentially clear liquids, but an analysis of trace elements should be provided.

At this time it appears that any foliar sprays should be anticipated for 2 weeks from now or slightly later if cool temperatures were to

FLOWER BUD INDUCTION ADVISORY #2 for 1998-1999-12/21/98

A best guess is that for non-water stressed trees, urea or phosphorous acid sprays should have been applied Sunday December 20 or Monday December 21 for enhancement of flower bud induction. Even if timing is optimum, induction temperatures have been low and the possibility of getting results is unknown.
So far this Fall-Winter, cool temperature induction of citrus flower buds continues to be low. We have had only one week of ideal temperatures. The weather prediction for the next 4 days is for 80 degree F highs. The weather prediction for the next front, Christmas weekend, does not promise that cool weather will follow. January is predicted to be above normal.

It is not likely that we will get a cool spell soon enough to continue flower bud induction. It is most likely that the trees will start flower bud differentiation of any available flower buds. Based on last weeks advisory, you should have sprayed to enhance flower bud induction on Sunday or today if you are not holding your trees back with water stress.

We do not know if the action of either urea or phosphorous acid to enhance stress induction of flower buds can be effective once the flower bud differentiation process starts. If these sprays can be effective, it will be for only a very few days, probably 3 or 4 at most. We have seen a response one year when we may have been 3 or 4 days into the differentiation process. It is certainly an economic risk (wasted spray costs) to treat later than 1 or 2 days into this current warm spell.
If you have water stressed your trees as suggested in earlier advisories, you can expect to continue the induction process if you did not receive substantial rain in this latest front. Most areas report less than ½ inch, but some areas did receive higher rainfall. To assure continued water stress induction, a higher level of stress is advisable this week to insure that the flower bud differentiation process cannot start even with high temperatures favorable for growth. Using water stress is similar to conditions in the tropics, where flower development does not start until enough rain or irrigation releases the trees from drought stress. A minimum of one more week of water stress is probably advisable and 2 weeks would be better. For processing oranges, this is probably a good idea to assure sufficient bloom for a reasonable crop. It is likely that this will be a year in which some June bloom will occur because of low Spring fruit sets.

For early crops of fresh fruit (navels and grapefruit particularly), urea sprays may boost flowering and cause an earlier bloom which is favorable for higher prices even though crop load may be fairly low. Even with urea and some water stress, it is likely that the resulting bloom will still be light. If so, some enhancement of flower and fruitlet set will be in order in the Spring bloom period.

If the weather predictions are wrong, we may get another induction period for more flower buds and a second bloom within the regular bloom period. This would be a repeat of last year, but with the first buds starting differentiation about 10 days later than last year. Last year we had very good induction later in January and early February. The weather predictions do not appear favorable for that. If January is warmer than normal, we can expect an early, light bloom.
We (graduate student Juan Valiente and I) have developed a technique to excise defoliated shoots from the tree, treat them to prevent desiccation and decay and force the buds to grow out in an apparently normal manner within about 10+ days in a growth chamber. So far we have seen few flowers in the emerging inflorescences. On Friday, shoots were put in the growth chamber after the past week of cool temperatures. Unfortunately, it will be another 10 days before we can determine if a substantial increase in flower bud induction had taken place. This methodology, which is currently supported by citrus box tax money, will allow us to evaluate induction conditions in a timely manner so that we can better understand the process. Further, it can be used to evaluate if enhancement techniques are working at different time intervals during or shortly after the induction period.

In summary, for the current situation, flower induction appears to be low based on cool temperature accumulation. Enhancement foliar sprays of urea or phosphorous acid are not likely to work after one or two more days, if for that long. If water stress has been established and it was not broken by the Sunday front, the stress should be continued for one or two more weeks. Irrigation should then follow and enhancement spray. This may provide a reasonable level of bloom within the normal bloom period.

Next week we will further assess what is happening to our normal abnormal Florida weather, how it is impacting us and if it may be advisable to start a prolonged drought stress treatment on some blocks to induce a reasonable late bloom in April. Such a water stress period needs to be 35 to 40 days and approximately another 30 days are required for the flower bud differentiation process to reach full bloom. But first we need a better assessment of our current flowering potential status which we will try to provide next Monday.

FLOWER BUD INDUCTION ADVISORY #3 for 1998-1999-12/28/98

We are progressing toward cool temperature induction of citrus flower buds but that progress continues to be slow. The Weather Service has lowered their temperature predictions following the Christmas weekend front. We can expect some additional induction temperatures this week as the short-term prediction is now for normal temperatures. January may still be above normal.
Last year we had very good induction later in January and early February. The weather predictions do not appear favorable for that, but usually January is the coldest month, and we can hope for continued cool weather. As of December 26th, accumulation of cool temperatures had reached 680 hours below 70 degrees F since November 1st at Lake Alfred. In your area, accumulated hours of cool temperatures may be a little different if you access the FAWN weather system. Coastal and South Florida locations accumulate less cool temperature than Northern Ridge areas. The FAWN system also shows accumulated hours since October 1st rather than from November 1st .
This 680 hours at Lake Alfred is about equal to the hours in 1994-83 when 50 % of the eventual flower buds had been induced. If the current projected cool spell lasts until next weekend, we could have as much cool weather as when 75 % of the flower buds had been induced in 94-83. In the year previous to that, the accumulated cool temperatures were nearly one and one half times as much at the same stage of flower bud induction. At this stage of our studies, we do not understand why those 2 years were that different in hours of cool temperature at the same stage of flower bud induction. We have been estimating our current status on the least stringent year but further work is necessary to, hopefully, understand and develop a meaningful equation for the relationship of cool temperatures to flower bud induction. The amount of warm temperatures that intervene during the Winter as well as the amount of the previous or current crop load may be important as negative effects on induction for the coming crop.
The buds that were induced prior to the high temperatures last week most likely started flower bud differentiation. Based on previous years, the induction process may continue in buds that require more cool temperatures to reach a satisfactory state for differentiation to begin. Last year is a good example of this phenomenon which will result in 2 sets of flower buds with different average bloom dates. The question is how much additional cool temperatures are needed to get another significant bloom.
If you had water stressed your trees before the warm spell, as suggested in earlier advisories, you can expect the induction process continued if you did not receive substantial rain. The new cool front should bring the trees to a reasonable level of combined stresses by the end of this coming week. A spray of either urea (25 to 28 lbs of N/acre) or phosphorous acid (2.6 qts/acre of 30 % product) to enhance stress induction of flower buds can be effective. The best guess for spray scheduling is early in the week of January 3rd. Continued cool temperatures or maintenance of water stress could allow a further delay, but general flower bud differentiation usually occurs by January 10 to 15 or earlier.
In summary, flower induction still appears to be low based on cool temperature accumulation, but hours are increasing. Enhancement foliar sprays of urea or phosphorous acid are not likely to work on non-water stressed trees until after some additional cool temperatures accumulate. If water stress has been established and was not broken by the recent fronts, the stress should be continued for at least one more week. If an enhancement spray is used, a through irrigation can then follow to push flower bud differentiation and early bloom. However, if cool weather is expected to continue, bringing the trees completely out of water stress is probably not advisable until after January 15th because of potential of a freeze.
A final advisory will be provided next Monday, January 4th. This would normally be the end of the recommended period for flower bud induction enhancement sprays. Later at bloom, we will recap our studies of flower bud induction for this year.

The progress of Florida citrus trees toward induction of citrus flower buds from cool temperatures has been favorable this past week with only part of one day warmer than desired. This week should continue to be very favorable and apparently without any freezing temperatures. The projection for Lake Alfred through Saturday 8 January is to have accumulated about 875 hours below 70 degrees F and 1125 hours below 75 degrees F. This will exceed the hours related to the 75 % induction stage for the 94-83 season. If next week is again cool due to another projected storm system moving East, we could accumulate as many induction hours as in 94-83. However, in the 93-94 season we accumulated an additional 900 hours below 70 degrees F compared to the 94-83 season or what we project for this year. 

It would appear that it is still likely to be a low flower induction year. Enhancement sprays on certain types of situations appear still in order. Timing should be the end of this week or early next week, if weather projections are for continued cold weather into next week. Delays beyond that are not advised as earlier studies in Gainesville showed that flower bud differentiation started, even that far North, by January 20th. 

Enhancement foliar sprays of urea or phosphorous acid may be useful since induction temperatures are still low. Priority situations for enhancement foliar sprays are blocks with high yields in this current crop, particularly Valencias since the current crop is still on the trees. Hamlins and other cultivars with a good crop this past year, particularly if not yet harvested, are likely to benefit also. Low bearing cultivars such as some Rhode Red Valencia strains, Ambersweet and navels usually bloom heavier than needed. This year might provide less flower competition because of the low amount of induction. Some tests have shown increased yields when flowering was purposely reduced or when gibberellic acid was applied at petal fall to increase fruit set in these cultivars. 

Several groves throughout the State have bloom or young fruit in post bloom stages. In these groves, about 1/3 rd of the tree surface had an early light to moderate flowering. These trees probably responded in tree canopy areas with very easy to induce buds to a combination of drought stress and the little cool weather in October and early November. The second set of flowers, also from easy to induce buds probably started differentiation about 20-22 December during the 4 to 5 day period with high temperatures above 80 degrees F. The last set of flowers will come from buds induced during the current cold period. Their differentiation may start with less warm temperature than the previous set but still should require some high 70 degree weather. 
In summary, induction by cool temperatures is on the low side and enhancement sprays may still be beneficial for the last wave of flower bud induction. We should expect distinct blooms or an apparent protracted bloom this year. Foliar nutrition sprays during the bloom period may be difficult to time because of a protracted bloom period. It may be best to apply a single spray timed when the fruitlets from the earliest flowering are well into the post bloom period and the later flower buds are still in an early bloom stage. 

This is the final advisory for this Winter. I hope they have proved useful and my best guesses are not too far wrong. I would appreciate email responses this Spring as to your observations of bloom intensity and spread, your enhancement sprays experiences, and if applied, did they appeared to help you bloom situation. We would be interested in how well the very early, December, bloom set for those who had such blocks.