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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11/13/2012

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

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

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

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

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

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

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

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

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.

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

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


12/03/2012

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

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

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

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

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

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

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

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


12/19/2012

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

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

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

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

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

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


1/02/2013

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

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

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

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

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

1/11/2013

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

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

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

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

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


4/09/2013

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

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

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

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

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

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

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