Flower Bud Induction Header

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

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11/5/2015

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.

1999-2000_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.

See a previous background introduction for previous important yield responses to cool temperatures: FLOWER BUD INDUCTION ADVISORY #1 for 2012-2013. 
If you have any questions, please contact me (albrigo@ufl.edu


11/24/2015

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. 
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.

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.

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


12/1/2015

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


12/15/2015

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.

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


12/23/2015

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.

I will not post another advisory until after New Year’s.  If you have any suggestions or questions, please contact me (albrigo@ufl.edu)


1/4/2016

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.

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


1/19/2016

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.  Please let me know what you see in your area (albrigo@ufl.edu).

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.

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


1/26/2016

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.

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


2/1/2016

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.

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


2/8/2016

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.

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


2/10/2016

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.

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


2/23/2016

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


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


3/10/2016

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.

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