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

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11/23/2011

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

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.

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.

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


12/09/2011

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.

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


12/20/2011

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.

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


1/11/2012

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.

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


2/28/2012

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. 

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


7/12/2012

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. 

This will be the last advisory for this year. If you have any questions, please contact me (albrigo@ufl.edu)