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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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11/10/2008

FLOWER BUD INDUCTION ADVISORY #1 for 2008-2009-11/10/08

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 

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 an ENSO-neutral year, average temperatures and rainfall.  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.  None of these adverse conditions appear to be in play for the coming seasons flower bud 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   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 an easy way to see if a warm period, which could trigger flower bud growth, is predicted for your specific area in Florida.

Some flower buds will be induced in the range of 350 to 450 accumulated hrs < 68 degrees F.  Warm events 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 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.  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 colored bands should be narrower as the level of potential flowering will 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 and required more hours for the peak bloom to occur, 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 flowering and crop per tree was still low resulting in only 166 million boxes of oranges.  This low yield 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 the previous year’s flower induction cycle.

Current status for 2008-09 Winter - The light to medium crops and general tree recovery without a hurricane should lead to a flowering response next spring more typical of citrus in Florida, unless an unusual event occurs.  This is supposed to be a ENSO-neutral winter with average cool temperature accumulation if warm periods do not interrupt the accumulation process.  Currently, citrus locations have accumulated low temperatures < 68 degrees F of 225 to 400 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 2009-10 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 over 750-800 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 or phone 863-956-1151)


11/24/2008

FLOWER BUD INDUCTION ADVISORY #2 for 2008-2009-11/24/08

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

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 2008-09 fall-winter – Improved tree condition of non-HLB affected trees since the 2004-05 hurricanes should be promising for good flowering next spring if cool weather accumulation continues.  Through November 23rd, citrus locations had accumulated low temperatures (< 68 degrees F) of 400 to 600 hours from southern to most northern areas, respectively.  The next 8 day forecast from NOAA calls for relatively cool temperatures and another 100 to 120 hours below 68 degrees F should accumulate.  The most northern FAWN site for citrus has now accumulated 622 hours and by next week this total should exceed 700 hours. The warmer southern areas will have about 500 hours. These values are ahead of last year at this time by over 150 hours, but last year was about 100 hours below the previous year.

If moderately cool weather continues for three more weeks, 2 weeks into December, the accumulation of cool temperatures in the southern areas would be marginally acceptable for an economic crop and acceptable (800 hours below 68 degrees F) for all other citrus areas in Florida.  At the same time prevention of growth during a winter warm spell is very important over the next 3 to 4 weeks in order to prevent initiation of bud growth too early.  Cool temperature accumulation is now at the level that bud growth of terminal buds could be easily initiated if a warm period occurred.   Therefore, continue to monitor and reduce irrigation amounts so drought stress can easily and rapidly occur if a warm period occurs between now and mid-December to Christmas.  Maintenance of water stress during this period also is an alternative to having sufficient cool temperatures for flower bud induction.  In recent studies, field trees held under some water stress had more flowers than trees irrigated during the winter. 

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 additional irrigation details.

The other side of winter conditions is concern for a freeze.  In this Neutral ENSO winter, freezes are more likely.  So far the early and continued cool weather should provide reasonable cold hardiness in the trees.  The Jet Stream flow is still mostly lateral from West to East across the southern half of the US so rapid Arctic Express cold air movement into Florida is not likely.  Check the Weather Underground on the CREC Weather links for easy access to Jet Stream patterns.

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.  In order to prevent bud growth, trees should be slightly stressed if a warm period (7-10 days with maximum temperatures above 85 degrees F.) is predicted.

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


12/16/2008

FLOWER BUD INDUCTION ADVISORY #3 for 2008-2009-12/16/08

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

Current status for 2008-09 fall-winter – Cool weather accumulation has continued at a good rate to the point that the induced buds are now very easy to stimulate into flower bud growth and differentiation.  The flowering monitor program indicates that the easy to induce buds have started to differentiate in the more northern locations (Avalon at 800 hours and Umatilla at 820 hours).  Other areas of the state may follow suit if temperature highs stay at 80 degrees F or higher for several days this week.  Through December 16th, citrus locations had accumulated low temperatures (< 68 degrees F) of 720 to 1000 hours from southern to the most northern areas, respectively.  The next 8 day forecast from NOAA calls for relatively cool temperatures and another 80 to 100 hours below 68 degrees F should accumulate.  The current values are acceptable for commercial crops in all areas except Ft. Pierce and more southern East Coast locations.  In another 8 days, the East Coast area should have an acceptable level of cool temperature accumulation also.

The northern areas have projected first bloom wave dates of February 2nd (Avalon) and February 6th (Umatilla) which, if correct, are very early and would put the flowers at risk to a potential frost.  Since the accumulated cool temperatures are in the 800s, the first wave of flowers should be the major wave for all of the citrus production areas.  During the past 3 years the trees have not responded by having their major bloom from this many hours of cool temperature accumulation.  If they do respond this year with the major bloom from the first initiation-differentiation wave, then the trees have probably finally returned to normal after the 2004-05 hurricanes.

The cool temperature accumulation is so good that I would advise trying to minimize growth through moderate drought maintenance rather than applying urea or phosphorous acid sprays to enhance flowering.   This is the most economical option as it saves spray and materials cost as well as some irrigation costs.  In all cases where the current crop is low to moderate, the return flowering should be very good without help.  Even if the current crop is a fairly heavy another two weeks should put induction levels at a high level, exceeding 1000 hours.

It is not advisable to start pushing growth of the trees as 1. An early February bloom is not desirable, and 2. Irrigating might reduce the cold hardiness level which should still be fairly good with the consistent cool temperatures experienced so far this fall and winter.  

The freeze hazard will be fairly high from now until January 15th.  In this Neutral ENSO winter, freezes are more likely.  The Jet Stream flow is still mostly horizontal from West to East across the southern two-thirds of the US so rapid Arctic Express cold air movement into Florida is not likely.  Check the Weather Underground on the CREC Weather links for easy access to Jet Stream patterns and watch it carefully over the next month for any significant change to a southern dip that can easily lead to freezing temperatures in Florida.

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 freeze period to view FAWN, use the on-line monitor site provided in the first advisory and the NOAA 8 day forecast and watch the Jet Stream pattern.  In order to prevent bud growth now that trees are at a high level of induction, trees should be slightly stressed if a warm period (5-7 days with maximum temperatures above 80 degrees F.) is predicted.

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


1/5/2009

FLOWER BUD INDUCTION ADVISORY #4 for 2008-2009-1/5/09

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 2008-09 fall-winter – Cool weather accumulation continued at a good rate to the point that the induced buds were easy to stimulate into flower bud growth and differentiation.  Sufficient warm weather occurred before Christmas in December for bud differentiation to start in all districts.  The flowering monitor program indicates that these easy to induce buds had started to differentiate from 2 December in the more northern locations (Avalon at 800 hours and Umatilla at 820 hours) until about 11 December in southern areas .  Many areas  of the state now have a second wave of bud growth with the start of that differentiation occurring just before Christmas.  Citrus locations had accumulated low temperatures (< 68 degrees F) of 695 to 1000 hours from southern to the most northern areas, respectively, when the first wave of differentiation started.  For Central to northern areas the second wave of buds had over 1000 hours of cool induction at the time of differentiation.  The southern areas should have a second wave of flower bud differentiation starting shortly.  The current values of flower bud induction are very acceptable for commercial crops in all areas.

The projected first bloom wave dates are from week one in February (Ft. Pierce, Ona, and Umatilla) to the second week in February for all other areas except Lake Alfred and Avalon.  The ‘flowering monitor system’ projects full bloom dates of 23 to 26 January for these two locations and bud swell is evident at Lake Alfred, but I don’t see any reason for bloom this early and assume that bloom at these two areas should fall in line with other areas to their north and south.  Therefore bloom at these locations also should be the first week of February.  Still this would be an early bloom and leave the trees very susceptible to a frost.  So far the Jet Stream pattern is favorable for minimizing our risk to a freeze, but there is a deep trough in the Jet stream over the Pacific Northwest that we should watch carefully to be sure it does not slide to the east (http://www.wunderground.com/US/Region/US/JetStream.shtml).

Since the accumulated cool temperatures for the start of the first differentiation are in the 700-800 range, the first wave of flowers should be the major wave for all of the citrus production areas.  However during the past 3 years (since the 2004 hurricanes) the trees have not responded by having their major bloom with only this many hours of cool temperature accumulation.  If they do respond this year with the major bloom from the first initiation-differentiation wave, then the trees have probably finally returned to normal after the 2004-05 hurricanes.

The cool temperature accumulation is very good, but I would advise trying to minimize growth through moderate drought maintenance rather than applying urea or phosphorous acid sprays to enhance flowering.  The bud development is past when these sprays should help and maintaining some drought stress is the most economical option as it saves spray and materials cost as well as some irrigation costs.  In all cases where the current crop is low to moderate, the return flowering should be very good without help.  Even if the current crop is fairly heavy the total induction level is high, exceeding 1000 hours.  Further, it is not advisable to start pushing growth of the trees as 1) an early February bloom is not desirable due to frost hazard and it would lead to early fruit maturation and poorer fruit quality, and 2) irrigating might reduce the cold hardiness level which should still be fairly good now if a freeze were to occur in the next two weeks.

The freeze hazard is usually fairly high from now until January 20th.  In a Neutral ENSO winter like this year, freezes are more likely.  As stated earlier, the Jet Stream flow is still mostly horizontal from West to East across the southern two-thirds of the USA but rapid Arctic Express cold air movement into Florida could occur if the Jet Stream trough moves to the eastern USA.

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 freeze period to view FAWN, use the on-line monitor site provided in the first advisory and the NOAA 8 day forecast and watch the Jet Stream pattern.  In order to prevent or delay bud growth now that trees are at a high level of induction and have some bud differentiation, trees should be slightly stressed if a warm period (5-7 days with maximum temperatures above 80 degrees F.) is predicted.

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


1/15/2009

FLOWER BUD INDUCTION ADVISORY #5 for 2008-2009-1/15/09

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.  This advisory was a quick update since cold weather was predicted for the weekend

Freeze potential according to Albrigo – The Jet Stream trough did move east from the Pacific Northwest and was bringing cold temperatures deep into Texas.  However as of today, the Jet Stream is turning East in North Texas and Oklahoma, maybe the Gators scared it north.  Warmer air is being drawn from the Gulf and lowest temperatures are now projected to be above the freezing point in most of the citrus growing area of Florida

Current status for 2008-09 fall-winter – We now have up to 3 flowering waves predicted.  Both in Lake Placid and Lake Alfred, there is a light wave of flower buds at pinhead stage.  There was more in Lake Placid, and they were more advanced than at Lake Alfred as of yesterday.  This first wave is much lighter than would be expected for 700 to 800 hours of cool temperatures so trees may still be behind their condition prior to the hurricanes.  We do now have a second wave projected in the south with 900 hours of induction and up to 3 waves projected from Sebring north with 1000 and 1200 hours respectively.  The first wave on most trees I have seen does not look significant and the major flowering should be expected in the later waves, which should come in mid-February and early March.  The dates of full bloom may be delayed if cool weather continues. 

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


3/6/2009

FLOWER BUD INDUCTION ADVISORY #6 for 2008-2009-3/6/09

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 the 2008-09 bloom and the 2009-10 crop – The 3 flowering waves have or are occurring as predicted.  However, the bloom dates were set back significantly by the relatively continuous cooler weather in January and February.  We now should have the major bloom waves the first two weeks of March and third week of March for Central Ridge, near the normal bloom date in recent years.  We have noticed that if cool weather occurs after the flower buds are growing and showing some extension the dates of full bloom are delayed.  Further development essentially stops until warmer temperatures occur again. The flowering monitor system does not reflect this late cold weather effect.

The first wave of flower buds was very light and these flowers froze in colder areas.  This flower loss will not have any impact on crop potential as flower numbers were very low. However, on trees that lost most of their mature leaves from freeze damage, heavier new vegetative flushes will compete with flower set of the later bloom waves resulting in a decrease in fruit set.  Hopefully, the flowering intensity of the second and thirds flowering waves will be heavy enough to still have reasonable fruit sets.  The second wave, with 900 to 1000 hours of cool temperatures, is blooming now (white pinhead to popcorn in the Central Ridge. Often this wave is mostly flowers (generative) with few leaves associated with the inflorescences.  There appears to be much better leaf development in the third wave of developing flower buds on trees that I have seen in Lake Placid, Lake Wales and Lake Alfred.  In our area, these flowers are at the small, green pinhead stage. The lack of leafy bloom in the second wave will depress fruit set, but the more leafy third wave is often substantial in numbers and should have a good set. Between these two flowering waves it looks like flowering intensity will be high enough to provide at least an average crop. After the fruit set period, by mid-May, the fruit set can be evaluated and a final advisory will be posted.

Freeze effects on bloom – A few things to remember about freezes and flowering:  Freezes do not enhance flowering intensity, in fact temperatures near freezing, probably up to near 40 degrees F, are too cold to add to the flowering intensity.  Developing more flowering intensity is a slow process and requires substantial hours of cool temperatures.  If leaves quickly drop off after a freeze, then little shoot damage has occurred and flowering will usually be normal.  If leaves dry up and remain attached to the twig, wood (cambial) damage has occurred and flower buds will not develop normally, usually die after initial push.  It usually takes more than 6 weeks to actually see how much wood damage occurred.

Watch these next two flowering waves, particularly the third wave for its intensity and leafiness.  If it is substantial in your blocks and the weather during bloom is good for bee activity, expect a good crop.  An advisory should be posted about mid-May to summarize our crop potential.

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



6/12/2009

FLOWER BUD INDUCTION ADVISORY #7 for 2008-2009-6/12/09

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

Summary for the 2008-09 bloom and the 2009-10 crop – The 3 flowering waves occurred as predicted.  However, the bloom dates were set back significantly by the relatively continuous cooler weather in January and February.  The major bloom waves were the last two, with the last occurring the third to fourth week of March for the Central Ridge, similar bloom dates to last year.  We have noticed that if cool weather occurs after the flower buds are expanding the dates of full bloom are delayed.  Further development essentially stops until warmer temperatures occur again. The flowering monitor system does not reflect this late cold weather effect.

The first wave of flower buds was very light and these flowers froze in colder areas.  This flower loss did not have any impact on crop potential as flower numbers were very low. However, on trees that lost most of their mature leaves from freeze damage, heavier new vegetative flushes competed with flower set of the later bloom waves resulting in a decrease in fruit set.  However, there were not many trees with heavy leaf loss so this situation is only important if it was your trees. Hopefully, the flowering intensity of the second and thirds flowering waves was heavy enough to still have reasonable fruit set on these trees.

The second wave of flowers, after 900 to 1000 hours of cool temperature induction, was mostly generative inflorescences with few leaves associated with the flowers. There was much better leaf development in the third wave of developing flower buds and this had the most intense flowering.  The third wave responded to 1214 hours (Lake Alfred) of inductive temperatures.  Therefore theses buds were difficult to induce which accounts for their higher leaf to flower ratio.  This leafy third wave should have been responsible for most of the fruit set.  From the second and third flowering waves total flowering intensity was high and sufficient to provide at least an average crop.

Weather was relatively cool during flowering and initial fruit set (low 80s to 88 in Immokalee from 18 March to 10 April) which delayed drop of the young fruit.  This resulted in a heavier drop during the May-June drop period.  The weather in late April and early May was back to normal with near 90 to low to mid-90s the first week of May.  The May-June drop occurred under normal conditions of hot, dry weather.  The last part of this drop wave occurred under an unusually early and long rainy period, but this rain probably was too late to alter the amount of drop very much.  Still, it no doubt was beneficial, particularly for good early fruit growth.  Some Indian River areas had difficulty meeting irrigation needs, which may have reduced fruit set on trees in these areas..

Overall, we should have at least a normal crop load for the trees we have left.  The question is how many mature trees do we have left, particularly in the southern third of the industry where huanglongbing took out larger numbers of trees this past year.  This year HLB may have a significant effect on industry-wide yield.  In my opinion, minus the tree losses, we should have a total crop similar to last year.

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

 



6/12/2009

FLOWER BUD INDUCTION ADVISORY #7 for 2008-2009-6/12/09

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

Summary for the 2008-09 bloom and the 2009-10 crop – The 3 flowering waves occurred as predicted.  However, the bloom dates were set back significantly by the relatively continuous cooler weather in January and February.  The major bloom waves were the last two, with the last occurring the third to fourth week of March for the Central Ridge, similar bloom dates to last year.  We have noticed that if cool weather occurs after the flower buds are expanding the dates of full bloom are delayed.  Further development essentially stops until warmer temperatures occur again. The flowering monitor system does not reflect this late cold weather effect.

The first wave of flower buds was very light and these flowers froze in colder areas.  This flower loss did not have any impact on crop potential as flower numbers were very low. However, on trees that lost most of their mature leaves from freeze damage, heavier new vegetative flushes competed with flower set of the later bloom waves resulting in a decrease in fruit set.  However, there were not many trees with heavy leaf loss so this situation is only important if it was your trees. Hopefully, the flowering intensity of the second and thirds flowering waves was heavy enough to still have reasonable fruit set on these trees.

The second wave of flowers, after 900 to 1000 hours of cool temperature induction, was mostly generative inflorescences with few leaves associated with the flowers. There was much better leaf development in the third wave of developing flower buds and this had the most intense flowering.  The third wave responded to 1214 hours (Lake Alfred) of inductive temperatures.  Therefore theses buds were difficult to induce which accounts for their higher leaf to flower ratio.  This leafy third wave should have been responsible for most of the fruit set.  From the second and third flowering waves total flowering intensity was high and sufficient to provide at least an average crop.

Weather was relatively cool during flowering and initial fruit set (low 80s to 88 in Immokalee from 18 March to 10 April) which delayed drop of the young fruit.  This resulted in a heavier drop during the May-June drop period.  The weather in late April and early May was back to normal with near 90 to low to mid-90s the first week of May.  The May-June drop occurred under normal conditions of hot, dry weather.  The last part of this drop wave occurred under an unusually early and long rainy period, but this rain probably was too late to alter the amount of drop very much.  Still, it no doubt was beneficial, particularly for good early fruit growth.  Some Indian River areas had difficulty meeting irrigation needs, which may have reduced fruit set on trees in these areas..

Overall, we should have at least a normal crop load for the trees we have left.  The question is how many mature trees do we have left, particularly in the southern third of the industry where huanglongbing took out larger numbers of trees this past year.  This year HLB may have a significant effect on industry-wide yield.  In my opinion, minus the tree losses, we should have a total crop similar to last year.

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