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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11/21/2013

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

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

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

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

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

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

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

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

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

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

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

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

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


12/03/2013

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

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

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

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

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

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

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

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


12/18/2013

FLOWER BUD INDUCTION ADVISORY #3 for 2013-2014-12/18/13

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

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: The weather has continued to be moderate with continued slow accumulation of inductive temperatures below the threshold for induction, <68 ° F. Currently,  415 to 750 cool hours have accumulated from southern to northern citrus areas.  An additional 50 to 100 hours from south to north are predicted to occur during the next week. The minimum hours in southern areas will therefore be above 475 hours of cool temperature induction at the end of another week (December 25th), which will be 300 hours below the minimum required for a good economic bloom if the current crop is low to moderate.  Central Florida areas, north of Sebring, should have accumulated 675 hours, 100 short of needed, while from Avalon north a minimum adequate accumulation of 800 hours of cool temperature induction should have occurred.  By Christmas with no more induction, it appears that bloom would be slightly less than adequate for next year’s crop in Central Florida and still deficient in southern areas.  However, cool temperatures are still forecast for a couple of days past Christmas and if these cooler temperatures continue until New Year’s Day even Central Florida would have adequate induction.  However, it is critical that you watch the weather for this Christmas to New Year’s period as a new advisory will not be posted until after the holidays.

With the higher induction levels that are now present, the buds will begin to grow if daytime high temperatures reach 80 ° F for just a few continuous days. Since cool temperatures are predicted to continue past next week, flower enhancing sprays may not be needed.  If a warm period that is forecast to last 5 or more days with maximum temperatures above 75-80 degrees F does occur before January 5th then with adequate soil moisture for growth, growers may consider applying a flower intensity enhancing spray of 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 (if 60 % P (3pts) or if 26 % P (2 qts)).  The chosen material should be applied in 80 to 125 gal of water/acre in the first 2 to 3 days at the beginning of the warm period. These products apparently increase the stress level and enhance the amount of flowering induced by the cool temperatures.  To follow the forecast, I recommend the Weather Channel which provides a 10 day forecast for a location near you, just type in a city in the location box.

Have you noticed that HLB affected trees with decline are flowering?  Look at medium defoliated branches to see if buds have flowers at pinhead stage.  Unfortunately these are not likely to produce useful fruit and they take away buds from next year’s potential crop.  The buds on these branches apparently were under stress, perhaps water stress, and received adequate flower bud induction.  With continual irrigation to minimize preharvest fruit drop these flower buds are growing.  Also I am sure you have noticed that Hamlin orange trees have accelerated their preharvest drop over the past 3 weeks.

Enjoy family visits over the holidays and try not to think too much about the misery of our citrus trees.  The next advisory will be the 6th or 7th of January.

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


1/09/2014

FLOWER BUD INDUCTION ADVISORY #4 for 2013-2014-1/09/14

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

Current Status:  The accumulated hours below the threshold for induction, <68 ° F, through January 8th were 700 to 1100 from southern to northern citrus areas.  Another 60 to 120 hours are predicted from south to north over the next 7 days. All citrus areas will have minimal (south Florida) to adequate (over 850 hours) induction levels after another 7 days. However this is about 100 to 200 hours (south to north) behind last year at this date.

Only the northern Florida citrus areas have initiation of flower bud development at this time (Avalon had initiation at 787 hours on December 20th with a projected full bloom date of February 26th).  At least another 300 hours have accumulated in this area and a second cohort of flower buds should start developing soon. Since cooler weather is usual in January the actual bloom date will probably be later, but still in early March, about normal. Across all the citrus production areas in Florida several days are predicted to be near 80 ° C or above during this coming week.  These temperatures are likely to initiate bud growth in most of the other citrus areas in Florida. At this time, I don’t recommend any flowering enhancement sprays, except perhaps in south Florida, since otherwise induction levels are good.

We slide by the first near freezing cold snap, but remember 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 artic air to rapidly travel south before it can warm up.  There are no immediate freeze warnings, therefore so far so good.

However, remember that applying spring ground fertilizer before the freeze hazard is over (last week of January) is not a good idea.  This is to protect from excessive fertilizer leaching if you need to use microjets for freeze protection.  Application in the first week of February is still enough time for fertilizer uptake by the trees for the spring flush and flowering, which looks on tract for no earlier than March 1st.

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


1/17/2014

FLOWER BUD INDUCTION ADVISORY #5 for 2013-2014-1/17/14

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

Current Status: This is a special report concerning the general bloom that is occurring now, at least throughout Central Florida.  It takes 45 to 60 days or longer for flower buds to develop to full bloom after growth is initiated.  Therefore the current bloom initiated growth in November at the latest.  This was before significant cool temperature induction had occurred.

At Lake Alfred, 208 and 406 hours below 68° F had accumulated by November 15th and 30th, respectively.  This suggests that the primary environmental induction factor was water stress.  There was a 35 day drought period after a 1.2 inch rain on October 7-8.  I am sure that most everyone was irrigating during that time, so normally this period would not have resulted in this large off bloom.

I believe this supports the idea that HLB affected trees are under water stress.  This stress likely occurs even with a normal irrigation program. We will be monitoring this and stress ethylene production this spring.

In the Immokalee area less cold and less rain occurred.  It should also have a general light bloom now.  Are you experiencing this light but general bloom?

Unfortunately this bloom uses up potential flower buds for the regular bloom period, while any fruit that matures from it will probably not be useful commercially.

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


2/3/2014

FLOWER BUD INDUCTION ADVISORY #6 for 2013-2014-2/03/14

NOTICE FOR CITRUS EXTENSION AGENTS & SPECIALISTS AND GROWER NEWSLETTERS

The following information has been developed as part of the Decision Information System for Citrus. 

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

Current Status: This is an alert concerning the probable first wave or cohort of bloom that in general is not predicted by the ‘Flowering Monitor System’.  In locations from Avalon north a first wave was predicted for late February full bloom.  However when queried by the model, all weather stations south of there did not indicate initiation of bud growth until the second cohort was predicted for Avalon.  Those predictions are for a full bloom of that cohort at the end of March to April 1st.

The lack of prediction of this first cohort may be due to marginal warm weather in late December, insufficient to trigger the model as it is now constructed.  But some growers have reported bud swell in southern areas suggesting that initiation of growth did occur throughout the state’s citrus industry around December 20th, the same as Avalon.  Unfortunately, the cool inductive hours <68° F, were not high at that time (463 in Immokalee and 659 in Lake Alfred) and another cohort of flowers is likely to occur from the second initiation that should result in a late March bloom.

If this scenario holds true, we should expect another extended bloom.

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


 

2/19/2014

FLOWER BUD INDUCTION ADVISORY #7 for 2013-2014-2/19/14

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

Current Status: Last advisory I discussed the lack of response of our model to the obvious current flower bud development and the stress induced bloom in January.   I recommend you bring up Avalon in the ‘Flowering Monitor System’ in order to get a truer picture of what is happening in your area.  Your area is likely to be a little ahead of Avalon. The prediction is for a full bloom of the current cohort by the end of February.  Remnants of the January bloom are overlapping into the beginning of this cohort.  A second regular cohort is predicted for the end of March to April 1st. If this scenario holds true, we should expect another extended bloom.  I am hoping that most of the available buds will flower in this cohort so that no buds will be available for a late March bloom.

For those of you trying to determine the cut off for spraying harsher chemicals for psyllid control, it is going to be difficult to determine when 10 % of the flowers in the current cohort are open since some of the first (stress induced) blooms are still opening.  At best less than 10 % open flowers will have passed by this weekend.

If there are very high flower counts in a 2 x 2 feet frame, you might try counting one square foot.  You can also take a ½ to ¾ inch diameter branch and count the total flowers and open ones on that branch.  It is relatively easy to keep track of where you are in the count on a branch if you are systematic as you move from the base through the branching.  A couple of these per tree side will be equivalent to a frame count.

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