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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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11/1/2006

FLOWER BUD INDUCTION ADVISORY #1 for 2006-2007-11/01/06

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

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

Overview of flower bud induction in Florida –  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 El Niño year, lower than average temperatures and higher than average rainfall. Usually under these conditions, enough hours of low temperatures below 68 degrees F. accumulate to induce a good 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 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.

In the 2004-2005 winter citrus trees that were not in the path of the hurricanes had two years of good to heavy crops so a high level of induction was needed to produce adequate flower buds for the 2005-06 crop. If the block was in the path of one to three hurricanes, and the trees lost fruit but not many leaves, the trees needed slightly less inductive temperatures since bud carbohydrate levels improved some, but fruit losses were after most of the summer-early fall drain on carbohydrates had occurred. If many leaves were lost along with the crop, then trees were fairly low in carbohydrate and needed high levels of inductive temperatures to produce a good bloom.

If heavy fruit and leaf loss stimulated a strong early fall flush, then more buds were available from the previous year’s spring and summer flush for flowering , as after Hurricane Charlie, but the fall flush did not mature adequately if flush was produced after Hurricane Jeanne. Generally, enough fall-flush matured to provide flowering for a crop of about 200-210 million boxes of oranges and 30 million boxes of grapefruit for the 2005-06 crop, a significant recovery, before tree losses to canker and fruit losses to Hurricane Wilma reduced the crop again.

The 2005-06 winter had cool periods and sufficient cool weather occurred to slow down or stop vegetative growth on mature trees and then 800 to 1200 hrs < 68 degrees F. accumulated from southern to northern districts, respectively, for the first flowering wave in late February. An additional 200 hours occurred in many districts for a second cohort of buds to flower in early to mid-March. In some locations, flower bud development had sufficiently progressed for a February 13-14 frost to damage the more advanced buds. To view specific FAWN data for a location near you in the citrus growing areas for the induction weather or the frost temperature use (www.crec.ifas.ufl.edu ) and click on FAWN under weather or for NOAA’s 8 day forecast go to Weather Links on our CREC homepage and then 8 day forecast. Although last winter’s cold induction was good, poor tree condition after one or two years of hurricanes and the spring frost lead to a low crop, predicted at 135 million boxes of oranges.

Current status for 2006-07 winter - The light crop and general tree recovery without a hurricane should be promising for good flowering next spring. Although this is supposed to be an El Niño winter with cooler and wetter than normal weather, better than average cool temperature accumulation can occur only if warm periods do not interrupt the accumulation process. Currently, citrus locations have accumulated low temperatures < 68 degrees F of 150 to 300 hours from southern to northern areas, respectively. The next 8 days will be average for cool temperatures and another 80 to 100 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 December 15 or 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.

(Request for potential cooperators) – Although rains in past winters often negated attempts to use drought stress to delay bloom in many areas, last winter was a good year to obtain this effect and growers that applied prolonged drought stress in late winter delayed bloom and avoided the damage to open buds caused by the February freeze. We are still interested in tests to delay bloom by managing irrigation to delay initiation of flower bud growth. This may be accomplished by withholding or restricting irrigation to prevent growth during warm winter periods until mid-January has passed. If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under this protocol, please contact me (albrigo@crec.ifas.ufl.edu or phone 863-956-1151).



11/7/2006

FLOWER BUD INDUCTION ADVISORY #2 for 2006-2007-11/7/06

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 2006-07 winter - The light crop and general tree recovery without a hurricane should be promising for good flowering next spring. Although this is supposed to be an El Niño winter with cooler and wetter than normal weather, better than average cool temperature accumulation can occur only if warm periods do not interrupt the accumulation process. Through November 6th, citrus locations had accumulated low temperatures < 68 degrees F of 160 to 300 hours from southern to most northern areas, respectively. The next 8 day forecast calls for cooler temperatures and another 100 to 140 hours < 68 degrees F should accumulate. The most northern FAWN site has now accumulated 400 hours and by next week this total should exceed 550 hours. (These numbers look suspiciously like a week ago, but that is what the program says). 

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. Therefore, start to monitor and reduce irrigation amounts so drought stress can occur if a warm period occurs between November 15 and December 15 or 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. See last weeks background advisory for irrigation details.

(Request for potential cooperators) – Although rains in past winters often negated attempts to use drought stress to delay bloom in many areas, last winter was a good year to obtain this effect and growers that applied prolonged drought stress in late winter delayed bloom and avoided the damage to open buds caused by the February freeze. We are still interested in tests to delay bloom by managing irrigation to delay initiation of flower bud growth. This may be accomplished by withholding or restricting irrigation to prevent growth during warm winter periods until mid-January has passed. We may be able to help you monitor this effort. If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under this protocol, please contact me (albrigo@crec.ifas.ufl.edu or phone 863-956-1151).

Note: There may not be an advisory next week as I will be traveling. Look at FAWN, use the on-line monitor and the NOAA 8 day forecast.


11/22/2006

FLOWER BUD INDUCTION ADVISORY #3 for 2006-2007-11/22/06

Please review the background information in the first advisory if you have not already done so.

Current Status:   Cool temperature accumulation has now reached 320 to 600 hrs < 68 degrees F., from southern to northern citrus districts.  Also, the National Weather Service (NOAA) predicts that there will be an additional 100 or more hours below < 68 degrees F. during the next 8 days.  To view specific FAWN data for a location near you in the citrus growing areas, use (www.crec.ifas.ufl.edu ) and click on FAWN or for NOAA’s 8 day forecast go to Weather Links on our CREC homepage and then the NOAA 8 day forecast.  See this season’s first advisory for how to run the flower monitoring system yourself.

This week’s cool weather should bring buds to a moderately low to moderate flower bud induction level where an extended warm period, 7 to 10 days with max. temperatures > 80 degrees F, would stimulate the easy to induce buds to begin differentiation.  Continued accumulation of cool temperatures and prevention of growth initiation during a winter warm spell are important to a good start for flower formation for the 2007-08 harvest season.  Therefore, keep irrigation amounts low or moderate (if fruit are still present) to minimize growth possibilities. Prepare to stop irrigation all-together and keep groves relatively dry, keep track of induction hours in your area, and watch NOAA’s 8-day forecast for possible warm weather that could force initiation of bud growth.  Remember this protocol is advised at least until Christmas. 

‘Plan ahead’  In a week or two, the advisory will discuss options if a warm spell prediction develops on the NOAA forecast for the period before Christmas.

(Request for potential cooperators) – Although rains this past winter negated attempts to use drought stress to delay bloom in many areas and collection of meaningful yields was severely disrupted by the hurricanes, we are still interested in tests to delay bloom by managing irrigation to delay initiation of flower bud growth.  This might be accomplished by withholding or restricting irrigation to prevent growth during warm winter periods until mid-January has passed.  If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under this protocol, please contact me (albrigo@crec.ifas.ufl.edu or phone 863-956-1151).  We will visit some potential cooperators next week.


11/30/2006

FLOWER BUD INDUCTION ADVISORY #4 for 2006-2007-11/30/06

Please review the background information in the first advisory if you have not already done so.

Current Status:  Cool temperature accumulation has now reached 490 to 800 hrs < 68 degrees F., from southern to northern citrus districts. Also, the National Weather Service (NOAA) predicts that there will be an additional 100 or more hours below < 68 degrees F. during the next 8 days. To view specific FAWN data for a location near you in the citrus growing areas, use (www.crec.ifas.ufl.edu ) and click on FAWN or for NOAA’s 8 day forecast go to Weather Links on our CREC homepage and then the NOAA 8 day forecast. See this season’s first advisory for how to run the flower monitoring system yourself.

This week’s warm weather is of some concern as it might be warm enough for long enough to stimulate initiation of some bud growth since bud condition has now reached the moderately low to moderate flower bud induction level in most districts. An extended warm period, 7 to 10 days with max. temperatures > 80 degrees F, might stimulate the easy to induce buds to begin differentiation. This week is very close to the threshold. Follow the Flower Monitor Program closely for your area for the next 3 or 4 days to see if it shows the initiation of a flowering event. If you had stopped irrigation and soil was dry before the rains of the last 3 days, you might have helped to avoid as early initiation of growth. NOAA predicts that a cold front will reach us this weekend. Follow the NOAA’s 8-day forecast for possible extension of the warm weather (stalled or diverted front). Extension of this warm period would almost guarantee initiation of bud growth if soil moisture is adequate. It is particularly advised to not irrigate until this warm spell ends and then manage for some stress until Christmas to stop any early growth.

‘Plan ahead’ Next week, I will discuss options if another warm period prediction develops on the NOAA forecast for the period before Christmas and we have less than 800 hours of cool temperatures..

(Request for potential cooperators) – Although winter rains often negate attempts to use drought stress to delay bloom in many areas of Florida, we are still interested in tests to delay bloom by managing irrigation to prevent initiation of flower bud growth. This might be accomplished by withholding or restricting irrigation to prevent growth during warm winter periods until mid-January has passed. We have had a couple of volunteers that have agreed to cooperate and could use some more. If you are interested in putting a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under this protocol, please contact me (albrigo@crec.ifas.ufl.edu or phone 863-956-1151). We will visit your site to set up the tests.


12/8/2006

FLOWER BUD INDUCTION ADVISORY #5 for 2006-2007-12/8/06

Please review the background information in the first advisory if you have not already done so.

Current Status: Cool temperature accumulation has now reached 530 to 900 hrs < 68 degrees F., from southern to northern citrus districts.  Also, the National Weather Service (NOAA) predicts that there will be an additional 75 to 110 hours below < 68 degrees F. during the next 8 days.  The 8 day forecast does not indicate that any significant warming trend is anticipated to start in the next 8 days. However, trees are now ready to initiate bud growth if a week-long warm period did occur. 

To view specific FAWN data for a location near you in the citrus growing areas, use (www.crec.ifas.ufl.edu ) go to Weather and click on FAWN or NOAA’s 8 day forecast.  See this season’s first advisory for how to run the flower monitoring system yourself.

Last week’s warm weather was of some concern as it appeared warm enough and long enough to stimulate initiation of some bud growth since bud condition had reached the moderately low to moderate flower bud induction level in most districts.  As of today, the Flowering Monitor Program does not indicate the initiation of a flowering event in any area except Umatilla, which has 900 accumulated cool hours.  In 2 weeks we plan to check in other areas to see if there is any bud swell of the first two buds at the terminal end of last year’s summer shoots.  If there is, then the program is over-estimating the amount of warm weather needed to stimulate bud growth.  In the past the monitor program has been very accurate at predicting initiation of growth.  This would be the first test as to whether it in some cases it may underestimate the number of flowering events in a season.  You can check your trees in a couple of weeks to see if any bud swell is evident.  If there is, please email that information so we can adjust the model.

If you had stopped irrigation and the soil was sufficiently dry to prevent growth during this past week, you should not have any bud swell in two weeks.  You should continue to keep the soil relative dry and stop irrigating if a warm period is predicted by NOAA.  It is particularly advised to manage irrigation for quick initiation of drought stress until Christmas to stop any early growth. 

‘Plan ahead’  It is time to start thinking about flower induction enhancing sprays (urea or phosphorous acid (PO3)).  They will be most useful if a warm period is predicted from near to shortly after Christmas and the total hours < 68 degrees F. has not reach 800 hours if you have a moderate crop and 900-1000 hours if you have a heavy crop.  If you are anticipating spraying one of these products, be sure you have material on hand.  For urea, you need 53 to 60 lbs of urea available per acre you plan to treat.  For a PO3 product you need 3 pints to 2 quarts per acre depending on which product you use (60 % P (3pts) or if 26 % P (2 qts) product).  If a warm period occurs immediately following next week, it may be advisable to spray trees with a good to heavy crop no later than 3 to 4 days into the warm period.  Next week, we will update the advisability of spraying by area.  Of course southern areas have the least inductive conditions.

I visited several Hamlin blocks yesterday in the Auburndale area to observe some light and heavy crops under the same management.  The high variability in crop load this year from block to block is more usual than unusual.  Leaf color and available vegetative flush for next year’s flowers was reasonable on all of the trees.  The heavy cropped trees had significant amounts of inside fruit as well as exterior fruit, while light crop trees had only outside fruit, and frequently, they had outside areas with little or no fruit.  The light crop trees had a lot of late bloom fruit from summer flowering, indicating just how light the normal crop is.  We will receive yield data for these blocks from before the 2004 hurricanes to see if they were out of phase at the time of the hurricanes or the first year after.  More on this when we get the data and try to explain some of the long-term hurricane effects we are observing. 

(Request for potential cooperators) – We still are interested in having growers put a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under a soil water deficit protocol to try to consolidate and/or delay spring bloom. If you are interested, please contact me (albrigo@crec.ifas.ufl.edu or phone 863-956-1151).  We will visit your site to help set up the tests.

 


12/14/2006

FLOWER BUD INDUCTION ADVISORY #6 for 2006-2007-12/14/06

Please review the background information in the first advisory if you have not already done so.

Current Status: Cool temperature accumulation has continued at a favorable pace in spite of temperatures being higher than expected, particularly as this is supposed to be an El Niño winter.  According to the Flowering Monitor System the citrus districts have now accumulated  610 to 1050 hrs < 68 degrees F., from southern to northern areas.  Also, the National Weather Service (NOAA) predicts that there will be an additional 84 hours below < 68 degrees F. during the next 8 days.  The 8 day forecast does not indicate that any significant warming trend is anticipated in the next week. However, trees are now ready to initiate bud growth if a week-long warm period did occur and the buds may initiate growth if daily highs continue to be near 80 degrees F.  This is because nearly two weeks of such weather have already occurred.  To view specific FAWN data for a location near you in the citrus growing areas, use (www.crec.ifas.ufl.edu ) go to Weather and click on FAWN or NOAA’s 8 day forecast.  See this season’s first advisory for how to access the Flower Monitor System on the Internet.

This week, the Flowering Monitor Program still does not indicate the initiation of a flowering event in any area except Umatilla, which has 1050 accumulated cool hours.  Balm data appears to be in error (over 1000 cool hours) and therefore shows initiation of flower bud growth.  Next week we plan to check for bud swell of the first two buds at the terminal end of last year’s summer shoots.  You can check your trees before Christmas to see if any bud swell is evident.  If there is, please email that information so we can adjust the model.

If you had stopped irrigation and the soil was sufficiently dry to prevent growth during the past 2 weeks, you should not have any bud swell.  You should continue to keep the soil relative dry and stop irrigating if a warm period is predicted by NOAA.  It is particularly advised to manage irrigation by using small applications so that quick initiation of drought stress will occur if you stop irrigation.  This protocol should be considered to prevent growth until after Christmas .

‘Plan ahead’ It is time to start thinking about flower induction enhancing sprays (urea or phosphorous acid (PO3)).  These sprays will be most useful if a warm period is predicted from near to shortly after Christmas and the total hours < 68 degrees F. has not reach 800 hours if you have a moderate to low crop and 900-1000 hours if you have a heavy crop.  These conditions would most likely exist in the southern citrus growing areas.  If you are anticipating spraying one of these products, be sure you have material on hand.  For urea, you need 53 to 60 lbs of urea available per acre you plan to treat.  For a PO3 product you need 3 pints to 2 quarts per acre depending on which product you use (60 % P (3pts) or if 26 % P (2 qts) product).  If a warm period occurs immediately following next week, it may be advisable to spray trees with a good to heavy crop no later than 3 to 4 days into the warm period. 

(Request for potential cooperators) – If you are interested in delaying the main bloom date by putting a block or a few rows of grapefruit, ‘Hamlin’ or ‘Valencia’ trees under a soil water deficit protocol, please contact me (albrigo@crec.ifas.ufl.edu or phone 863-956-1151).  We will visit your site to help set up the tests.  Those that are following this protocol should continue to allow water stress when warm weather is predicted until the end of January.


12/8/2006

FLOWER BUD INDUCTION ADVISORY #7 for 2006-2007-12/20/06

Please review the background information in the first advisory if you have not already done so.

Current Status: According to the Flowering Monitor System the citrus trees (buds) have accumulated 620 to 1150 hrs < 68 degrees F., from southern to northern areas.  Also, the National Weather Service (NOAA) predicts that there will be an additional 130 hours below < 68 degrees F. during the next 8 days.  The 8 day forecast does not indicate that any significant warming trend is anticipated in the next week, but daytime highs will continue to be fairly warm for this time of year and an El Niňo year.. To view specific FAWN data for a location near you in the citrus growing areas, use (www.crec.ifas.ufl.edu ) go to Weather and click on FAWN or NOAA’s 8 day forecast.  See this season’s first advisory for how to access the Flowering Monitor System on the Internet.

This week, the Flowering Monitor Program still does not indicate the initiation of a flowering event in southern areas, but Lake Alfred and Umatilla do indicate bud growth with an early to mid-February bloom date estimate.  But trees in many areas have initiated bud growth after the warm weather from late November through mid-December. I have one report of bud swell on trees in 2 or 3 areas south of Lake Alfred.  I believe it may be a general condition in most areas.  Have you checked some of your trees to see if any bud swell is evident? 

Those two or three weeks of warm weather (highs just below or above 80 degrees F.) apparently were sufficient to initiate growth if soil moisture was available. At the time this bud growth started trees had accumulated from the mid-500s to 650 hours of cool temperatures.  This is on the low side for best flowering.   If you had stopped irrigation and the soil was sufficiently dry during most of the period from the November 16th rain until the December 14th rain occurred, you may not have any bud swell.  Particularly if you are in the southern areas, you should continue to keep the soil relative dry and stop irrigating if another warm period is predicted by NOAA during the next two weeks.  Manage irrigation by using small applications so that quick initiation of drought stress will occur if you stop irrigation.  Let me know if you don’t see any bud swell in non-irrigated blocks.

‘Plan ahead’ There is still time to use flower induction enhancing sprays (urea or phosphorous acid (PO3)).  Although in many or most cases the first wave of flower buds has started to grow, there will be further induction of other buds.  At the time of the next warm period, the level of flowering in those buds can be increased by one of these sprays.  The decision to spray should be based on how much additional cool weather occurs from December 14th until the warm period and if the total hours < 68 degrees F. has not reach 850 to 900 hours.  If total hours exceed 1000 hours or the additional hours from December 15th exceed 500 hours at the beginning of the next warm period, I would not spray.  For urea, you need to apply 53 to 60 lbs of urea per acre.  For a PO3 product you should apply 3 pints to 2 quarts per acre depending on which product you use (60 % P (3pts) or if 26 % P (2 qts) product). 


1/3/2007

FLOWER BUD INDUCTION ADVISORY #8 for 2006-2007-1/3/07

Currently, all citrus areas have flower buds swollen and in many cases young leaflets are pushing. The Flowering Monitor System indicates this growth started about 10-12 December and the projected bloom dates for this first wave of flowers is about February 7 to 9 if normal or warmer weather continues. This first wave was induced at about 600 to 800 accumulated hours below 68 degrees F from southern to northern districts. The most northern district may flower even earlier, late January. If you are in this area you should examine flower buds to see if the first two buds on summer shoots are expanded to the exposed leaflet stage. If they are not, then the bloom date may be a little later than projected by the Flowering Monitor System. After the initiation of the first wave another 200 to 250 hours of cool temperatures have accumulated. It is likely that another wave of flower buds will initiate growth at the end of this week as daytime highs are projected to continue at above 75 degrees F. The bloom date for this wave would probably be in early March. The total accumulated hours will be from 700 to 1100 hours depending on the citrus growing district. The lowest levels of induction will be in the southern districts, particularly the Indian River. In those districts with low total induction, trees with a heavy crop or weak re-growth after the hurricanes may benefit from a spray of urea or PO3. Review the last advisory for more information about these sprays. If you choose to treat some acreage, these sprays should be applied at temperature near or above 70 degrees F. and within the next 5 to 7 days. There are some anticipated side effects of this year’s weather and projected two waves of flowering that will be about 1 month apart and cause a prolonged bloom period. This will make psyllid control more difficult. Also with an El Nino year and higher probability for spring rains, some post bloom fruit drop may emerge by the second flowering period. See the extension information at http://www.crec.ifas.ufl.edu/extension/fungal/diseases.shtml for more details about this potential problem. (Questions?) – If you have any questions regarding flower bud induction and flower development, please contact me (albrigo@ufl.edu or phone 863-956-1151 ext 1207).


1/11/2007

FLOWER BUD INDUCTION ADVISORY #9 for 2006-2007-1/11/07

Currently, two waves of flower buds have initiated growth and some flower buds in the first wave are swollen and young leaflets are pushing from a few, most advanced vegetative buds (Fig 1 to 3).  The Flowering Monitor System indicates this growth started about 10-12 December and the projected bloom dates for this first wave of flowers is now February 4 to 5, if normal or warmer weather continues as it has this past week.  This first wave was induced at about 600 to 800 accumulated hours below 68 degrees F from southern to northern districts.  The most northern district (Umatilla) may flower even earlier, 21 January. 

After the initiation of the first wave another 200 to 250 hours of cool temperatures accumulated before the second wave initiated growth.  This wave of flower buds is projected to bloom in early March (March 2 to 5).  The total accumulated hours will be from 800 to 1050 hours depending on the citrus growing district.  The lowest levels of induction are in the southern districts, particularly the Indian River (only 600 hours for the first wave and 720 for likely second wave). 

Flower induction is essentially over.  Now we can wait and see if the bloom dates will really be as early as projected.  I only saw a scattered amount of buds with leaflets exposed, but the other buds will jump forward in development if we get another week of 80 degree weather.

Even if the 2 projected waves of flowering come later than early February and March, they will still be about 1 month apart and cause a prolonged bloom period.  This will make psyllid control more difficult.  Also with an El Nino year and higher probability for spring rains, some post bloom fruit drop may emerge by the second flowering period.  See the extension information at http://www.crec.ifas.ufl.edu/extension/fungal/diseases.shtml  for more details about this potential problem.

The crop potential for trees with a good current crop from the first wave of inducted buds will be weak, but the second wave had a moderate level of induction and maybe a medium crop can be anticipated overall for these trees.  For light cropped trees, a reasonably heavy crop should occur if we have finally gotten over the residual hurricane effects.  The real question is how many of each kind of tree do we now have? 

(Questions?) – If you have any questions regarding flower bud induction and flower development, please contact me (albrigo@ufl.edu or phone 863-956-1151 ext 1207).

 


1/17/2007

FLOWER BUD INDUCTION ADVISORY #10 for 2006-2007-1/17/07

Currently, two waves of flower buds have initiated growth and some flower buds in the first wave are swollen, pushing out young leaflets on the most advanced vegetative buds and some pinhead flowers are now visible in most orange cultivars.  The Flowering Monitor System indicates this growth started about 10-12 December and the projected bloom dates for this first wave of flowers are now February 2 to 6.  This first wave was induced at about 600 to 800 accumulated hours below 68 degrees F from southern to northern districts.  According to the model, the most northern district (Umatilla) may flower even earlier, 21 January.  The only good thing I can say about this early flush is that it is a small percentage of the available buds and hopefully, the second wave will have most of the flowering, at a reasonable date.

This second wave of flower buds is projected to bloom in early March (March 2 to 5).  The total accumulated hours will be from 800 to 1050 hours depending on the citrus growing district.  The lowest levels of induction are in the southern districts, particularly the Indian River (only 600 hours for the first wave and 750 for a likely second wave).

Flower induction is essentially over.  Now we can wait and see if the bloom dates will really be as early as projected.  Last week I doubted the model, but the few buds that are pushing are expanding rapidly.  I saw 2 or 3 inflorescences that were already an inch long with pinhead flowers.

Even if the 2 projected waves of flowering come later than early February and March, they will still be about 1 month apart and cause a prolonged bloom period.  This will make psyllid control more difficult.  Also with an El Nino year and higher probability for spring rains, some post bloom fruit drop may emerge by the second flowering period.  See the extension information at http://www.crec.ifas.ufl.edu/extension/fungal/diseases.shtml  for more details about this potential problem.

The crop potential from the first wave of inducted buds appears to be low, but the second wave has a moderate level of induction and maybe a medium crop can be anticipated overall for these trees.  For light cropped trees, a reasonably heavy crop should occur if we have finally gotten over the residual hurricane effects.  The real question is how many of each kind of tree do we now have?

Florida temperatures are projected to be cooler the next few days, but citrus bud development should still progress so that the level of flowering in the first wave can be more accurately evaluated by next week. 

Have you started your fertilizer program yet?  The atmospheric jet stream pattern is still mostly from West to East so there is little chance of a freeze, particularly as we will be past the 20th this weekend with no evidence of a severe cold front coming down on us from the North.  The main bloom should be about the first week of March.  Fertilizer should be in the tree 1-2 weeks before that date. 

(Questions?) – If you have any questions regarding flower bud induction and flower development, please contact me (albrigo@ufl.edu or phone 863-956-1151 ext 1207).


1/26/2007

FLOWER BUD INDUCTION ADVISORY #11 for 2006-2007-1/26/07

Flower bud induction is now stable and no changes in induction levels will occur. Currently, two waves of flower buds have initiated growth and some flower buds in the first wave are swollen, pushing out young leaflets on the most advanced vegetative buds and some pinhead flowers are now visible in most orange cultivars.  The Flowering Monitor System indicates this growth started about 10-12 December.   The first wave was induced at about 600 to 800 accumulated hours below 68 degrees F from southern to northern districts.  The projected bloom dates have moved up so that the first wave of flowers may occur next week, just before 1 February or even earlier.  The early flush still appears to be a small percentage of the available buds and hopefully, the second wave, end of February, will have most of the flowering. 

The bloom date for this second wave of flower buds has moved up from the 1st week of March (March 2 to 5).  The total accumulated hours will be from 800 to 1050 hours depending on the citrus growing district.  The lowest levels of induction are in the southern districts, particularly the Indian River (only 600 hours for the first wave and 750 for a likely second wave).  This week, flowers were evident on weak trees in the River District.  We traveled to some citrus near Alligator Alley, below Clewiston, and saw many open flowers on the weaker trees.  The healthier trees had pinhead to popcorn and some open flowers.  Again these trees did not have a large percentage of their buds at this stage but other buds were swollen.

Even if the 2 projected waves of flowering come later than early February and March, they will still be about 1 month apart and cause a prolonged bloom period.  This will make psyllid control more difficult.  Also with an El Nino year and higher probability for spring rains, some post bloom fruit drop may emerge by the second flowering period.  See the extension information at http://www.crec.ifas.ufl.edu/extension/fungal/diseases.shtml  for more details about this potential problem.  The flowering model does project that a third wave of flowering could happen by mid-March, further extending the flush-bloom period.

The crop potential from the first wave of inducted buds appears to be low, but the second wave has a moderate level of induction and maybe a medium crop can be anticipated overall for these trees.  For light cropped trees, a reasonably heavy crop should occur if we have finally gotten over the residual hurricane effects on tree canopy condition.  The real question is how many of each kind of tree do we now have?

Florida temperatures are projected to be cooler next week, but freezing temperatures are not predicted as far north as Leesburg, so hopefully none of the first wave of flowers will be lost.  The atmospheric jet stream pattern is still mostly from West to East so there is little chance of a freeze.

Have you started your fertilizer program yet?    The main bloom should be about the last week of February to the first week of March.  Fertilizer should be in the tree at least 1-2 weeks before that date.   Next weeks cold weather should not delay bloom very much.  Continued cold weather after next week could delay bloom, but probably not more than 1 to 1 ½ weeks.

(Questions?) – If you have any questions regarding flower bud induction and flower development, please contact me (albrigo@ufl.edu or phone 863-956-1151 ext 1207).


2/6/2007

FLOWER BUD INDUCTION ADVISORY #12 for 2006-2007-2/6/07

Flower bud induction is now stable and no further changes in induction levels should occur. The first wave of flower buds initiated growth in early December, but was a small number of the total available buds.  This wave of buds has flowered or is doing so now.  Overall, the induction level when these flower buds started their growth was low.  In the Central Florida area, the current cool weather has delayed this bloom a few days.  Some trees in all districts have more flowers in this wave than is the general case for healthy trees.  The stage of flowering is more advanced on these trees than on most trees with smaller amounts of open flowers also.

The bloom date for the second wave of flower buds is still projected to be around the 1st week of March.  The total accumulated hours is from 800 to 1050 hours depending on the citrus growing district.  Continued cool weather may delay the full bloom date, but probably not more than a week to 10 days at most.  Although more buds are starting to show swelling and bud break, there are still many buds on apparently suitable flowering shoots not showing any growth, although some are swelling.

This suggests that the projected third wave of flower opening may occur as projected in mid-March.  All areas would have over 1100 hours below 68 degrees F. for that flowering wave.

The crop potential from the first wave of inducted buds appears to be very low although more flowers were evident on trees in the more southern areas, the second wave now appears to be a moderate level of induction, but not enough buds are developing yet.  Hopefully, more flowers will develop in a third wave of flowering.  The projection of temperatures in the mid-70s later this week should cause more advancement and within the next two weeks we should be able to see most of the growing buds for this spring’s flush.  Then we can better assess our crop potential for the 2007-08 harvest season.

(Questions?) – If you have any questions regarding flower bud induction and flower development, please contact me (albrigo@ufl.edu or phone 863-956-1151 ext 1207).


2/14/2007

FLOWER BUD INDUCTION ADVISORY #13 for 2006-2007-2/14/07

Flower bud induction is now stable and no further changes in induction levels should occur. The first wave of flower buds initiated growth in early December, but was a small number of the total available buds.  This wave of buds has flowered.  Overall, the induction level when these flower buds started their growth was low.  In the Central Florida area, the current cool weather delayed this bloom a few days.  Some trees in all districts have more flowers in this wave than is the general case for healthy trees.  This wave will result in little fruit set on most trees.

The bloom date for the second wave of flower buds is still projected to be the end of February to the 1st week of March.  A total of 800 to 1050 hours accumulated for this flowering wave  depending on the citrus growing district.  Continued cool weather may delay the full bloom date, but probably not more than a few days at most.  Although more buds are starting to show swelling and bud break, there are still many buds on apparently suitable flowering shoots not showing any growth, although some are swelling.  Based on the trees observed in Lake Alfred, it appears that there will be buds available for the projected third wave of flower opening as projected for mid-March.  All areas have over 1100 hours below 68 degrees F. for that flowering wave.

In estimating the full bloom date remember that although a full bloom is projected for the majority of flowers at that stage, there is bud to bud variability and some flowers may open a week earlier or later than the average date.  Also look at several trees within and between blocks.  We have two Valencia blocks with very different proportions of flowering buds showing for the early March bloom.  One block has many more buds pushing than the other, but neither has all of the available spring or summer shoots showing bud growth.

The main concern for this week is the projected cold weather on Saturday morning.  If the projected low materializes on the Ridge and cold air drains to the low areas towards Arcadia and Immokalee, a large amount of the flush and flowers could be damaged.  The National Weather Service is projecting 30 and 33 degrees F for the lows Saturday morning in Lakeland and Winter Haven, respectively.  Everyone needs to keep a very close eye on the weather and evaluate multiple sources for low temperature projections.

(Questions?) – If you have any questions regarding flower bud induction and flower development, please contact me (albrigo@ufl.edu or phone 863-956-1151 ext 1207).


2/28/2007

FLOWER BUD INDUCTION ADVISORY #14 for 2006-2007-2/28/07

It looks like we will finally have the major bloom for 2007 in mid-March.  The projected full bloom date for this wave is from March 17 to 21 depending on the citrus area. Will these buds reach full bloom in 3 weeks?  The one anomaly in the ‘Flowering Monitor System’ is that Umatilla reportedly is past full bloom for all waves.  I would appreciate some reports from the area north of Tavares as to whether this third wave is more nearly at the same stage, early feather growth, as is evident in central areas.  Although more trees in the southern areas had substantial flowers in the earlier waves, trees examined this week from Lake Placid to Lake Alfred now have many buds breaking and new growth is mostly at the earliest feather stage with evidence of at least one flower mixed with the leaves in many of the buds.  Tree to tree and canopy to canopy location variability is large with some canopy areas having considerable second wave flowers near full bloom, while other trees and canopy locations have few of these flowers, but many buds pushing or at least visibly swollen.

I thought that the second wave would be the major bloom, but it is going to be the third wave.  This is good because on most trees, at least on the Ridge, we do not have enough flowers to provide an economic crop in the first two waves.  Obviously, we still have work to do in order to understand all of the factors interacting with induction temperatures to determine how many buds can break and grow as flower buds for a given temperature induction level.  A major factor determining flowering level is carbohydrates in the buds, but I had assumed that most trees, at least on the Ridge, are finally at adequate carbohydrate levels for a normal bloom after the 2004 hurricanes.  There probably are some additional factors still to be understood.

Information from previous advisories

Flower bud induction is now stable and no further changes in induction levels should occur. The first wave of flower buds initiated growth in early December, but was a small number of the total available buds.  This wave of buds has flowered.  Overall, the induction level when these flower buds started their growth was low.  In the Central Florida area, the cool weather delayed this bloom a few days.  Some weaker trees in all districts had more flowers in this wave than is the general case for healthy trees.  This wave will result in little fruit set on most trees.The bloom date for the second wave of flower buds was projected to be the end of February to the 1st week of March.  This is holding true.  A total of 800 to 1050 hours accumulated for this flowering wave depending on the citrus growing district.  Although more buds were growing in this second wave, there were still many buds on apparently suitable flowering shoots not showing any growth, although some were swelling.  Based on the trees observed in Lake Alfred, it appears that there will be buds available for the projected third wave of flower opening as projected for a mid-March bloom.  All areas have over 1100 hours below 68 degrees F. for that flowering wave.

In estimating the full bloom date remember that although a full bloom is projected for the majority of flowers at that stage, there is bud to bud variability and some flowers may open a week earlier or later than the average date.  Also look at several trees within and between blocks.  We have two Valencia blocks with very different proportions of flowering buds showing for the early March bloom.  One block had many more buds pushing than the other, but neither had all of the available spring or summer shoots showing bud growth.

(Questions?) – If you have any questions regarding flower bud induction and flower development, please contact me (albrigo@ufl.edu or phone 863-956-1151 ext 1207).


3/7/2007

FLOWER BUD INDUCTION ADVISORY #15 for 2006-2007-3/7/07

It definitely looks like we will finally have the major bloom for 2007 in mid-March.  The projected full bloom date for this wave is from March 16 to 20 depending on the citrus area. Will these buds reach full bloom in 2 weeks?  In the Lake Placid area, many of these inflorescence shoots are an inch long and large pinhead, but still green blossoms are visible.  On the central Ridge, the growth is shorter, but many buds have feather leaves and small pinhead flowers. These should expand rapidly.  Many shoots are showing this condition, with the most vigorous summer shots having fewer buds growing.  Although in some canopy zones, a lot of this growth is vegetative only, the majority of the new growth has one or more flowers now visible.

In central Florida, the second wave is just at full bloom or at the popcorn stage.  This is about a one week delay from the originally predicted bloom date.  On trees in the southern Ridge area, these blossoms are slightly more advanced.  Some trees have a fair amount of this stage, but in the locations I have seen it does not equal the flowering coming in the third wave for mid-March. Fruit from the first wave are about ¼ inch diameter.

By the middle of next week, we should be able to assess the blossom numbers in the inflorescences and establish the typical flower to leaf ratio.  New leaf production in mixed inflorescences is important to setting fruit through the May-June drop period.  How many buds on each shoot are flowering is a good indicator of what the overall crop potential will be.  We can revisit these issues next week.

(Questions?) – If you have any questions regarding flower bud induction and flower development, please contact me (albrigo@ufl.edu or phone 863-956-1151 ext 1207).


3/19/2007

FLOWER BUD INDUCTION ADVISORY #16 for 2006-2007-3/19/07

he major bloom for most trees in 2007 will be at least next week or a little later (25 to 30 March).  The projected full bloom date for this wave was from March 16 to 20 depending on the citrus area, but just as the second wave of flowers was about a week to 10 days late due to cooler weather, this larger wave will follow the same delay.  In central Florida, this last wave looks strong with flowers ranging in development from pinhead to a few in the popcorn stage.

In an average year, 80 % of the flowers occur in the first 4 terminal end bud positions (4 leaf axis).  It appears that many shoots have 5 to 7inflorescenses (buds) that will produce flowers, but of course some have none. This may be a bit above average and most of the buds have produced mixed inflorescences with a fair number of leaves.  This speaks well for the next crop to be back to normal.

Data from one Central Florida grower indicates that 4 Hamlin blocks had still not recovered to normal production with this 2006-07 harvest.  This was apparently due to lingering effects of the three 2004 hurricanes.  All of these blocks are producing a heavy flowering wave now that appears to be at normal levels and similar to most trees in this area.

At what level will next years crop be?  If we have good numbers of remaining mature trees after the hurricanes, canker, development and greening losses of grove, then we should be able to project our likely level of recovery.

(Questions?) – If you have any questions regarding flower bud induction and flower development, please contact me (albrigo@ufl.edu or phone 863-956-1151 ext 1207).


4/5/2007

FLOWER BUD INDUCTION ADVISORY #17 for 2006-2007-4/5/07

In the last advisory I stated that ‘The major bloom for most trees in 2007 will be at least next week or a little later (25 to 30 March)’.  In fact for most trees, full bloom has just pasted early this week.  That is about a 2 week delay from the model, partially due to cooler weather, but the result is clearly the major bloom for the year.  Bloom the first week of April has occurred before and the crop that develops will likely be later in maturing.  Further, there is good flowering inside most canopies as well as in the outer canopy.  If fruit set is normal, we should have a good to very good yield per tree.  Will fruit set be normal?

We are at the beginning of the hot, dry spring period that occurs every year.  In the past 30 years, there have been only a handful of cases where climatic conditions were extreme enough to change the normal pattern of fruit set.  Of course if you don’t irrigate during this period until the June rains start, fruit set will be significantly reduced (R.C.J. Koo, 1960s).

In 2 months we can revisit the situation and see if any unusual weather pattern occurred.  For now, provide good irrigation scheduling and if your trees are healthy, you should have a good crop this year.

(Questions?) – If you have any questions regarding flower bud induction and flower development, please contact me (albrigo@ufl.edu or phone 863-956-1151 ext 1207).


6/13/2007

FLOWER BUD INDUCTION ADVISORY #18 for 2006-2007-6/13/07

The major bloom for most trees in 2007 was in late March to early April.  Bloom the first week of April has occurred before and the crop that develops will likely be later in maturing.  Further, there was good flowering inside most canopies as well as in the outer canopy.

At bloom time, the major issue became ‘Will fruit set be normal?’  The answer is yes.  We should have a very good yield per tree, especially compared to the two previous years.

Examination of trees in the Auburndale-Lake Alfred area indicated that set is good, very little drop will occur from this point until neat harvest.  Just an occasional yellowing fruit was observed and mostly on Valencia trees.  Unfortunately, I have not observed set in more southern regions and the coast, but bloom was similar in all areas, late and heavy.  Fruit set in some southern areas may be adversely affected if irrigation was restricted due to water shortages.

Fruit size is golf ball for Hamlin and a little smaller for Valencia.  Grapefruit were of course bigger as were navel fruit.  The only trees that showed much set from earlier flowering waves were navels.  Fruit size may be a little behind some years, but the late bloom did allow early development in warmer than normal temperatures and the result was a fast start on fruit growth.

The major issues for what our  2007-08 harvest will be are hurricanes, freezes and how many mature trees we have left.  Temperatures (warm ocean waters) will favor major hurricanes, but it is anyone’s guess as to their path.  The winter temperatures and rainfall will follow a Neutral or La Nina pattern, which increases the chance of a freeze.  Barring one or more of these catastrophes, we should have a very good crop, but the tree census is still being worked on.  We haven’t had a good crop on our reduced tree numbers to see what the new medium and high production levels can be.  Some people have said that they expect a new high would be in the low 200 million box level.  The fruit set appears to be a little short of whatever the new potential is.

(Questions?) – If you have any questions regarding flower bud induction, flower development and fruit set,  please contact me (albrigo@ufl.edu or phone 863-956-1151 ext 1207).