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

Select date

 

2/16/2017

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.



2/15/2017

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.

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


1/17/2017

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.

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


1/3/2017

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.

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


12/20/2016

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.

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


11/29/2016

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


11/15/2016

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.  

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


11/1/2016

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.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).