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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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11/01/2007

FLOWER BUD INDUCTION ADVISORY #1 for 2007-2008-11/01/07

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 
Citrus Research & Education Center, Lake Alfred, FL 

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).  A period 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 a La Nina year, higher than average temperatures and lower than average rainfall.  Even under these conditions, enough hours of low temperatures below 68 degrees F. usually accumulate to induce a reasonable level of flower buds.  Conditions that can interfere with good flower bud induction include: 1) several warm periods interrupt the induction process or 2) the previous crop was exceptionally high or 3) leaf loss from hurricanes or other causes (canker) was excessive and tree recovery was not complete.  Two or three lead to low carbohydrate levels in developing buds which reduced their ability to become flower buds.

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   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 (400-500 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 year’s (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.shtml.  This is the easiest way to see if a warm period, which could trigger flower bud growth, is predicted.

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 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 is roughly mid-November to mid-December.  Then additional flower buds develop later resulting 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 of cool periods.  Sufficiently cool temperatures will 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.  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 the greener shaded bands should be broader (require more hours for the same level of flowering).  If the current crop is lighter or tree condition better, then the bands should be narrower as the level of potential flowering would be greater at lower total cool temperature hours. Although this representation does not appear on the working screen, recommendations (bottom text box) 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 and may be accessed at: http://orb.at.ufl.edu/DISC/bloom.

1999-2000_bloom 
Weekly or bi-weekly advisories will follow this preliminary one 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 low (640 hours accumulated), 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 small crop occurred (2002-03 crop).  By late December in the winter of 2002-2003, we had 850 hours of uninterrupted cool inductive temperatures with a low current crop on the trees. The following warm period initiated almost all the buds on all of the spring and summer flush to differentiate and bloom in early March.  Still 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 October Florida citrus crop forecast by the Florida Agric. Statistical Service ever (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 crop.  Since then, we have had Hurricane Wilma in 2005, a long period of tree recovery from the 2004 and 2005 hurricanes plus tree losses from canker eradication.  Until this year, flowering levels have been low probably because of continued tree recovery after the multiple hurricanes.  This past year accumulated hours below 68 degrees F were more than acceptable by the second warm period (over 1000 hours) but it was not until the third warm period with over 1150 hours accumulated that the major flowering wave was triggered.  This high level probably indicated 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 last year’s flower induction cycle.

Current status for 2007-08  winter - The heavier crop and general tree recovery without a hurricane should lead to average flowering next spring, unless an unusual event occurs.  Although this is supposed to be a La Nina winter with warmer and dryer than normal weather, average cool temperature accumulation if warm periods do not interrupt the accumulation process.  Currently, citrus locations have accumulated low temperatures < 68 degrees F of 45 to 150 hours from southern to northern areas, respectively.  The next 8 days will be below average cool temperatures and another 140 to 168 hours should accumulate. Continued accumulation of cool temperatures and prevention of growth during a winter warm spell are important for a good start for the 2007-08 citrus production.  Therefore, start to monitor irrigation amounts so drought stress can occur if a warm period occurs between November 15 and Christmas, depending on the rate of cool temperature accumulation and reaching an acceptable level of 800 hours.  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.

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


11/21/2007

FLOWER BUD INDUCTION ADVISORY #2 for 2007-2008-11/21/07

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 
Citrus Research & Education Center, Lake Alfred, FL

Please review Advisory #1 for this year if you have not done so.  Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data.

Current status for 2007-08 winter - The general continued tree recovery since the 2004-05 hurricanes should be promising for good flowering next spring if cool weather accumulation is favorable.  Although this is supposed to be a La Nina winter with warmer and dryer than normal weather, average or better cool temperature accumulation can occur if warm periods do not interrupt the accumulation process.  Through November 20th, citrus locations had accumulated low temperatures < 68 degrees F of 225 to 375 hours from southern to most northern areas, respectively.  The next 8 day forecast calls for relatively cool temperatures and another 100 to 140 hours < 68 degrees F should accumulate.  The most northern FAWN site has now accumulated 380 hours and by next week this total should exceed 530 hours. The warmer southern areas will have about 340 hours. These values are behind last year at this time by about 100 hours.

Continued accumulation of cool temperatures and prevention of growth during a winter warm spell are important for a good start for the 2007-08 citrus production.  After next week we could have bud growth initiated if a warm period occurred as these values will approach those needed to have buds that are easy to stimulate into growth.  Therefore, start to monitor and reduce irrigation amounts so drought stress can occur if a warm period occurs between now and Christmas.  With the better crop this year, an acceptable level of cool temperature accumulation would probably be at least 800 hours.  Maintenance of water stress during this period is an alternative to having sufficient cool temperatures for flower bud induction.  The last two years field trees held under some water stress had more flowers than trees irrigated during the winter.  A La Nina year favors the ability to maintain water stress as it should be dryer than normal.

At the very least, 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. See last week’s background advisory for irrigation details.  There are two useful Websites to follow weather forecasts.  The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click.  Alternative, an 8 day forecast can be viewed by going to www.crec.ifas.ufl.edu and click on resources> weather> 8-day forecast.  Remember during this critical period to view FAWN, use the on-line monitor site provided in the first advisory and the NOAA 8 day forecast.  Trees should be slightly stressed if a warm period is predicted (7-10 days with maximum temperatures above 85 degrees F.) in order to prevent bud growth.

If you have further questions, please contact me (albrigo@ufl.edu or phone 863-956-1151).


12/05/2007

FLOWER BUD INDUCTION ADVISORY #3 for 2007-2008-12/05/07

Please review Advisory #1 for this year if you have not done so.  Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data

Current status for 2007-08  Winter - Although this is supposed to be a La Nina winter with warmer and dryer than normal weather, average or better cool temperature accumulation can occur if warm periods do not interrupt the accumulation process.  Unfortunately so far, this year is behaving like an average La Nina winter.  Through December 4th, citrus locations had accumulated low temperatures < 68 degrees F of 340 to 550 hours from southern to most northern areas, respectively.  The next 8 day forecast calls for cool nights, but moderate daytime temperatures with another 100 to 140 hours < 68 degrees F accumulating.  The most northern FAWN may accumulate another 150 hours by next week and exceed 700 hours. The warmer southern areas will have about 450 hours. On 12 December, these values will be further behind last year by about 160 to 300 hours from the southern to northern citrus areas. 

Even though cool temperature accumulation is lower than last year, the trees will have reached induction levels at the end of this cool period that make the buds very vulnerable to stimulation of bud growth by a warm period.  A week with daytime highs in the mid-80s would probably promote growth of the terminal-most 2 to 3 buds.  If that next warm period comes before New Year’s, it is very important for soil moisture to be low so that bud growth is suppressed by mild drought conditions.

Therefore, you should be monitoring and reducing irrigation amounts so drought stress can occur if a warm period is predicted and occurs between now and Christmas.  Since the next few days will be relatively cool, be careful not to over water.  The trees don’t need much soil moisture at this time.  With the better crop this year, an acceptable level of cool temperature accumulation would probably be at least 800 hours. The trees are not likely to reach that level of cool temperature induction.  Maintenance of water stress during this period is an alternative to having sufficient cool temperatures for flower bud induction.  The last two years field trees held under some water stress (no irrigation) had more flowers than trees irrigated during the winter.  A La Nina year favors the ability to maintain water stress as it should be dryer than normal.  If there is no rain, you may need to bump soil moisture up periodically with light irrigations.  Do not apply normal, full volume irrigations until it is time to purposely stimulate bud growth, sometime in January at the earliest.

By now you should have groves with relatively dry soils in the lower rooting depths from withholding heavier irrigations. Keep track of induction hours in your area and watch for the next advisory. See the initial background advisory for more irrigation details.  There are two useful Websites to follow weather forecasts.  The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click.  Alternative, an 8 day forecast can be viewed by going to www.crec.ifas.ufl.edu and click on resources> weather> 8-day forecast.  Trees should be slightly stressed if a warm period is predicted (7-10 days with maximum temperatures above 85 degrees F.) in order to minimize bud growth.

In the next advisory we will review the use of foliar urea or phosphorous salts (PO3) at the beginning of a warm time period in order to enhance flowering intensity when cool temperature induction is inadequate.  This may be very useful this year, particularly in southern regions, if rains raise soil moisture levels at lower rooting depths and warm weather occurs before Christmas.  The background and last year’s advisory may be reviewed for more information.

If you have further questions, please contact me (use only albrigo@ufl.edu until the next advisory)


12/20/2007

FLOWER BUD INDUCTION ADVISORY #4 for 2007-2008-12/20/07

Please review Advisory #1 for this year if you have not done so.  Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data

Current status for 2007-08  Winter - This is a La Nina winter with warmer and dryer than normal weather, and so far, this year is behaving like an average La Nina winter.  Through December 19th, citrus locations had accumulated low temperatures < 68 degrees F of 490 to 760 hours from southern to most northern areas, respectively.  The next 8 day forecast calls for cool nights, but moderate daytime temperatures with another 80 to 110 hours < 68 degrees F accumulating.  The most northern FAWN may reach a satisfactory 850 hours of temperatures < 68 degrees F. The warmer southern areas will only have about 575 hours of temperatures < 68 degrees F shortly after Christmas.  This is probably 150 to 200 hours short of a good minimum for a satisfactory flowering level on trees with a good current crop.

Although most areas received rainfall this past week, FAWN data indicates that only northern areas reportedly received soil saturating amounts.  The cool temperatures this week should have allowed soil drying so that drought conditions may exist again when a warm period starts.  It is advisable to continue dry soil conditions for at least another 2 to 3 weeks while cool inductions temperatures continue to accumulate.  If a warm period (7 days above 83-85 degrees F) occurs before then with adequate soil moisture for growth, growers should consider applying either 53 to 60 lbs of foliar urea/acre in 80 to 125 gal of water, 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) product).  This should be applied in the first 2 to 3 days at the beginning of the warm period..

See the initial background advisory for more irrigation details.  There are two useful Websites to follow weather forecasts.  The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click.  Alternative, an 8 day forecast can be viewed by going to www.crec.ifas.ufl.edu and click on resources> weather> 8-day forecast.  Trees should be slightly stressed if a warm period is predicted (7-10 days with maximum temperatures above 85 degrees F.) in order to minimize bud growth.  This practice should continue if possible until we reach 750 to 800 hours below 68 degrees F or a warm period starts after a saturating rain at which time urea of PO3 should be applied to enhance the level of flower induction.

Keep track of induction hours in your area.   Because of the holidays, the next advisory will not be posted until after New Year’s Day.  If you have further questions, please contact me (use only albrigo@ufl.edu until the next advisory)


1/02/2008

FLOWER BUD INDUCTION ADVISORY #5 for 2007-2008-1/02/08

Please review Advisory #1 for this year if you have not done so.  Besides background, it provides web sites to run the Flowering Monitor System on-line and other related links for weather data.

Will favorable weather last for two more weeks?  If so, we will have a decent flower bud induction period for next year’s crop.

Current status for 2007-08  Winter –This is a La Nina winter with warmer and dryer than normal weather, and so far, this year is behaving like an average La Nina winter.  The good aspect is that no prolonged warm period has occurred and therefore we are still accumulating flower bud induction.  Through December 30th, citrus locations had accumulated low temperatures < 68 degrees F of 615 to 935 hours from southern to most northern areas, respectively.  The next 8 day forecast calls for cool nights, a possible freeze but moderate daytime temperatures with another 95 to 120 hours < 68 degrees F accumulating.  The most northern areas will exceed 1000 hours of temperatures < 68 degrees F. The warmer southern areas will have about 720 hours of temperatures < 68 degrees F by next week.  This is probably 100 hours short of a good induction level for satisfactory flowering on trees with a good current crop.

Perhaps of some interest is that according to the Citrus Flowering Monitor System, Citra has two flowering waves developing for mid and late February blooms.  This clearly indicates that other areas will have trees responding to moderate temperatures with bud growth in the near future.  Buds will probably begin to push if 4 or 5 days in the low 80s occur. 

Some areas received rainfall this past week, and more may occur on the cold front approaching now.  The cool temperatures this week should allow soil drying before a warm period starts.  It appears that we can get another week of induction after this coming week, particularly if no additional rains occur.  If however a warm period (5 to 7 days above 80 degrees F) starts early next week with adequate soil moisture for growth, growers in the more southern regions should consider applying either 53 to 60 lbs of foliar urea/acre in 80 to 125 gal of water, 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 (2qts) product).  These sprays should be applied in the first 2 to 3 days at the beginning of the warm period.

As to the freeze potential for tomorrow, conditions are favorable for temperatures to be above those predicted by NOAA.  There is only a moderate dip in the Jet Stream, the dip is west of the Eastern states, but the temperatures over southern Texas are cold.  There is a northern draft on the eastern side that may draw warmer temperatures out of the Gulf.  That could also bring clouds to help.  Maybe this is just looking for the best hope for high 20s to low 30s in the citrus belt, but watch the Jet Stream and today’s highs!

There are two useful Websites to follow weather forecasts.  The Florida Agricultural Weather Network (FAWN) now has an easy access function to the NOAA 4 day forecast, just type location and click.  Alternatively, an 8 day forecast can be viewed by going to www.crec.ifas.ufl.edu and click on resources> weather> 8-day forecast.  A link to Weather Underground is also available.  Trees should be slightly water stressed if a warm period is predicted (now 5-7 days with maximum temperatures above 80 degrees F.) in order to minimize bud growth.  This practice should continue if possible until we reach 750 to 800 hours below 68 degrees F or a warm period starts after a saturating rain at which time urea or PO3 should be applied to enhance the level of flower induction.

If flower bud growth were to start in early January, we could expect a March 1st bloom.  If you have some interest in having a later bloom, this can be accomplished if you can maintain some drought stress until late January, past the 20th.  This of course depends on rainfall and temperatures, but would bring about a late March bloom with more flowers and a later maturation of the crop.  Think about it for some Valencia blocks.

 Keep track of induction hours in your area. If you have further questions, please contact me (863-956-1151 or albrigo@ufl.edu)



1/8/2008

FLOWER BUD INDUCTION ADVISORY #6 for 2007-2008-1/8/08

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 
Citrus Research & Education Center, Lake Alfred, FL

Currently, all central to northern citrus areas have flower buds initiated and growing.  The flowering Monitor System indicates this growth started about 20-22 December and the projected bloom dates for this first wave of flowers is about February 28 to 2 March if normal or warmer weather continues.  This first wave was induced at about 800+ accumulated hours below 68 degrees F from Sebring to northern districts.  Another 200 hours has accumulated and a second wave of buds will be initiated to flower shortly.

For Immokalee and Ft. Pierce the model does not indicate that bud growth has started, but I expect bud growth initiation will start this week.  Currently trees have been exposed to 730 to 760 hours of inductive temperatures.

In these areas with low total induction, trees, particularly with a heavy crop, may benefit from a spray of urea or PO3.  Review the last advisory for more information.  These sprays should be applied at temperature near or above 70 degrees F. and within the next week.

If you have any questions, please contact me (albrigo@ufl.edu or phone 863-956-1151).


1/18/2008

FLOWER BUD INDUCTION ADVISORY #7 for 2007-2008-1/18/08

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 
Citrus Research & Education Center, Lake Alfred, FL

Currently, all central to northern citrus areas have flower buds initiated and growing.  Southern areas such as Ft. Pierce and Immokalee probably have bud growth also, but the Flowering Monitor System does not indicate that this has happen, even though there are now 880 to over 900 hours below 68 degrees F in those areas. The Flowering Monitor System indicates this bud growth started about 20-22 December in most areas and the projected bloom dates for this first wave of flowers is from February 22 to 27 if normal or warmer weather continues.  This first wave was induced at about 640 to 800+ accumulated hours below 68 degrees F from Sebring to northern districts.  Another 200 hours has accumulated and a second wave of buds is initiated, and they should reach peak flowering March 11 to 14th.

Trees, particularly with a heavy crop and in areas with low total induction, , may still benefit from a spray of urea or PO3,but that time will probably be past one week after the next cold front goes by.  Review the 5th advisory for more information.  These sprays should be applied at temperatures above 70 degrees F.

Some blocks over-flower and set poorly.  Some Valencia selections have this problem, and mandarin blocks with a light crop also are good candidates for a spray of 10 ppm GA3 at 125 gal/acre.   The best timing for this spray is probably the end of next week if temperatures warm up to above 70 degrees F. 

If you have any questions, please contact me (albrigo@ufl.edu or phone 863-956-1151).


2/11/2008

FLOWER BUD INDUCTION ADVISORY #8 for 2007-2008-2/11/08

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 
Citrus Research & Education Center, Lake Alfred, FL

Currently, all citrus areas have flower buds initiated and growing.  Southern areas such as Ft. Pierce and Immokalee have bud growth that started at 830 to 840 hours below 68 degrees F. Most areas had two waves of bud break and the second usually started at about 1000 hours.  The Flowering Monitor System indicates this bud growth started about 22 December to early January in most areas and the projected bloom dates for this first wave of flowers is from February 27 to early March for most areas.  The second wave is projected for mid-March. The bloom dates have shifted forward about 6 days from the model projections made soon after bud differentiation started. Data for Avalon appears to be incorrect for the bloom dates as projected for now and the second in late February. The bloom projection lines are also out of proper alignment. 

It is now time to ride out flower bud development and note when peak blooms do occur in relationship to the projections.  Stressed limbs and trees, notably HLB affected trees, may be in full bloom.  Trees with easily seen flowering are suspect for stress problems.  Healthy trees with a reasonable crop are showing a few pinhead inflorescences.  Navels, other oranges, grapefruit and finally mandarins are advancing in that order towards full bloom.

Although most trees had good canopy recovery last spring, they may have still been affected by the hurricanes since in most cases the major bloom did not occur until the last flowering wave, after 1150 hours of inductive temperatures.  The first (almost no flowers) and second (light flowering) waves occurred after 800 and 1000 hrs of inductive temperatures, respectively.  In previous years, we would have expected most of the flowering to occur in the first two waves, not essentially all in the third. 

Hopefully, flowering waves will be back to normal with the first two waves this year having significant flower numbers from the mid-800 to 1000 hours of inductive temperatures.  You should watch these flowering waves to see if they both have significant numbers of flowers develop.   If they do, the result should be good flowering levels for all trees except those that had a very heavy crop this harvest season.    There have been additional cool hours, so all is not lost if the first two waves do not show normal behavior.

If we haven’t lost too many trees to diseases this year and tree health continues to improve, the next crop could exceed this season’s.  Unfortunately, many blocks in the south may have lost more than 10 % of their trees to HLB.  I’ll try to assess tree numbers, flower numbers and potential crop next advisory in late February, about the time projected for the initial bloom. 

If you have any questions, please contact me (albrigo@ufl.edu or phone 863-956-1151).


3/4/2008

FLOWER BUD INDUCTION ADVISORY #9 for 2007-2008-3/4/08

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 
Citrus Research & Education Center, Lake Alfred, FL

Currently, the flowering process is underway. In most cases, it appears that the first wave of flowers is fairly light as it was last year.  It is also the result of about the same level of cool temperature induction as last year (830 to 840 hours below 68 degrees F). There is considerable tree to tree variation and the exact date of this wave being in full bloom is difficult to judge.  It does appear that it occurred in February but maybe not as early as the Flowering Monitor Program was predicting in early February.  However, in January the prediction was for the last week of February.   The second wave of flowering buds is much larger and the differentiation of this group of buds started after 1015-1020 hours of cool induction.  The full bloom date of this second wave is projected for the end of this week. This flowering wave should make a reasonable crop from observations locally, in Sebring and grower reports.

There is a possible 3rd wave to come at the end of March to early April.   If this materializes, it will be from about 1200 hours of cool induction.  This would be about the level that led to the heaviest bloom last year. From what I see, I think that most of the buds are pushing and this possible last wave will not be very strong and maybe will occur only on some trees. 

It is hard to believe that there may still be a carryover effect from the hurricanes but at 830 inductive temperatures hours again there is only a fairly light bloom.  In previous years, we would have expected stronger flowering at this induction level.  At least this year, the second wave of flowers is strong enough apparently to minimize heavy flowering in a third wave of flowering buds.. 

In 2 weeks we can look at a final summary of the flowering this season and assess our crop potential

If you have any questions, please contact me (albrigo@ufl.edu or phone 863-956-1151).


3/27/2008

FLOWER BUD INDUCTION ADVISORY #10 for 2007-2008-3/27/08

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 
Citrus Research & Education Center, Lake Alfred, FL

Although the flowering process is almost over, there are still some popcorn flowers and occasionally even a new inflorescence at pinhead stage.  The date of full bloom has turned out to be later than projected by the ‘Citrus Flowering Monitor’ system’.  I would say full bloom date was a week later than those predicted and closer to March 12 in Lake Alfred and March 18 in Sebring.  Observations and the model agree that full bloom was later in Sebring than Lake Alfred.  Usually, they have been reversed and less than 6 days apart.  In most cases, overall flowering is better than last year.  So far so good, but there still fruit set and growth to go.  Usually, these factors are fairly steady and don’t contribute very much to yield variation.

It is hard to believe that there may still be a carryover effect from the 2004-05 hurricanes but the predicted 2007-08 yield per mature tree equivalents (MTE) supports that the effect was still in place this year.  The lateness of the heaviest flowering wave was a clue, but went unheeded by yours truly.  Based on the NASS-Fla. Citrus Statistics projections and assuming a 5 % loss of trees from the 2006 tree inventory, early-midseason cultivars are producing about 3.75 boxes per MTE and late cultivars 2.85 boxes per MTE this season.  MTE is calculated based on tree age and average yields of that age compared to full size (mature) trees.  For 40 years, the MTE yields have been 3.8 to 5.5 and 2.9 to 4.3, respectively, for early-mids and late cultivars.  As you can see, this year’s yields are at the bottom of the ranges for each harvest range. 

So what does next season hold in store for us!  If you don’t mind my behaving like an economist and making some assumptions, here might be the scenario:  We had a bloom equal to or slightly better than last year; Since bloom was still primarily in a later than expected wave of flowering, the trees are still not completely happy and will not set nor size fruit at their upper potential; We lose another 5 % of trees to disease and development; The remaining bearing trees come in just below or at an average yield per tree.  This means that yield next season can be greater than this season, but any increase in Florida’s yield next season should be more than offset by an expected decrease of 10 to 20 % in Brazil’s production. 

This is the last planned advisory for this year.  If you have any questions, please contact me (albrigo@ufl.edu or phone 863-956-1151).