Flower Bud Induction Header

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

Select date

 

11/28/2005

FLOWER BUD INDUCTION ADVISORY #1 for 2005-2006-11/28/05

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 is progressing for the coming year's bloom. Low temperatures first stop growth and then promote induction of flower buds as more hours of low temperatures accumulate (below 68 degrees F). A period of high temperatures in winter can then initiate bud differentiation which after sufficient days of warm springtime temperatures leads to bloom. The meteorologists predict that this winter in Florida will be a neutral El Ni ñ o year, average temperature and rainfall. Usually under these average conditions, enough hours of low temperatures below 68 degrees F. should accumulate to induce a moderate to 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 the previous year. Two or three lead to low carbohydrate levels for developing 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 850 hours below 68 degrees F. If the crop load is light, sufficient flower bud induction can occur after 700 to 750 hours of accumulated low temperatures. A warm period of 7 to 12 days, with maximum temperatures > 75 to 80 degrees F., can trigger growth (bud swelling) after a minimum of low temperatures have accumulated (500 hours below 68 degrees F). Fewer days and lower daytime highs in a warm period are required to stimulate growth of buds later in the winter when the accumulated cool temperature induction hours are high. Current and previous year's weather information relative to Florida citrus flower bud development can be obtained from the Florida Automated Weather System (fawn.ifas.ufl.edu) for locations near you. The 8 day forecast from the National Weather Service predicts Florida weather for several sites around the citrus belt and is linked to http://www.crec.ifas.ufl.edu/crechome/crecweather.shtml

Some flower buds will be induced in the range of 300 to 600 accumulated hrs < 68 degrees F. Warm events 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. This situation results in multiple cohorts of flower buds developing to different bloom dates. During the years from 1963 to 2004, multiple blooms occurred in over half of the years. Historically, the time period in which a early warm 7-12 day period can lead to some buds growing and then additional bud develop result in multiple blooms is roughly mid-November to mid-December. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is to promote water stress by stopping irrigation before these predicted warm periods occur. If the warm periods(s) are of the typical 7 to 10 day duration, a 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 of 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. The 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 recent years.

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. This 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. Some added information in color or bold lettering is intended to assist with interpretation. The level of potential flowering would be greater (orange line) with a light crop or less (green line) with a heavy crop for the same amount of hours of induction. 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. We are working to make the system available on-line shortly. In the meantime, the weekly advisories will update accumulating hours of related temperatures and other weather effects on flower bud induction. Methods for enhancing or reducing 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.

1999-2000_bloom 
Previous 4-year's results – In the winter of 2001-2002 cool temperature accumulation was very slow, 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. By late December in the winter of 2003-2003 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. 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 FASS October crop forecast for Florida ever. In 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 hurricanes.

Last year 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 current year's 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 could improve 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 fall flush, then more buds were available on last year's spring and summer flush for flowering if the fall flush came 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 210 million boxes of oranges and 30 million boxes of grapefruit, a significant recovery, before tree losses to canker and fruit losses to Hurricane Wilma reduced the crop potential again.

The new season's situation – Two cool periods have occurred this Fall. Sufficient cool weather has occurred to slow down or stop vegetative growth on mature trees, 320 to 630 hrs < 68 degrees F., from southern to northern districts. An additional 80 to 108 hours are predicted for the next 8 days. No steady warm period is predicted for these 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 8 day forecast.

The major concern for the next 20 days is the possibility of an extended warm period, 10 to 12 days with max. temperatures > 75 to 80 degrees F, in early to mid-December which would initiate differentiation of easily induced flower buds. Continued accumulation of cool temperatures or prevention of growth during a winter warm spell is important for a good start for the 2006-07 citrus crop. Therefore, keep irrigation amounts low to moderate (if fruit are still present) to minimize growth possibilities. 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 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).


 


12/05/2005

FLOWER BUD INDUCTION ADVISORY #2 for 2005-2006-12/05/05

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

Current Status: Cool temperature accumulation has now reached 420 to 760 hrs < 68 degrees F., from southern to northern citrus districts. Also, the National Weather Service (NOAA) predicts that there will be about 96 to 110 additional 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.

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 to the 2006-07 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.

By next week, it will be appropriate to consider a urea or phosphorous acid spray if a warm spell comes by Christmas and it is not possible to stop bud development by maintaining drought stress. Next week, I will review the protocol for those sprays and their timing at the beginning of a warm spell. Remember that materials and properly working sprayers are needed for these sprayers. Aerial application needs to be arranged in advance. ‘Plan ahead' A midweek advisory will be posted if a warm spell prediction develops on the NOAA forecast.

(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).


12/13/2005

FLOWER BUD INDUCTION ADVISORY #3 for 2005-2006-12/13/05

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

Current Status: Accumulated cool weather has now reached 490 to nearly 900 hr < 68 degrees F. from southern to northern citrus districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be 168 additional hours below 68 degrees F. during the next 7 days (max temperatures below 68 degrees F. for 1 week). This means that all areas will be at least in the moderate range of flowering potential by next week. The cooler districts should reach the first stage of the high range, exceeding 900 hours. 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 8 day forecast.

Up to now, cool temperature accumulation has been at a good, almost constant rate. Two more weeks of cool weather will place all districts in a good position. This requires the NOAA 8-day forecast to continue in the plus 100 hrs per week range until Christmas. Rainfall has prevented soil moisture from depleting to provide drought conditions which could inhibit flower buds growth. So a warm period in December will now stimulate the terminal buds on spring and summer shoots to initiate growth. A sufficient warm period is probably 5 to 7 days in the low-80s.

If we are in the 800 accumulated hours < 68 degrees F. range when a warm period starts, you may want to consider using a flower bud induction enhancing spray of either urea or phosphorous acid (PO3. 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). Trees with severe defoliation from hurricanes this summer followed by a strong fall flush may be good candidates for these sprays this winter since their buds may be harder to induce to be flower buds. Sprays can be applied at low volume, even aerial if with a good distribution system. Application time should be just as the warm period is starting, when daytime highs are in the 70 degree range, and may continue for up to a week. Sprayed trees will often bloom up to a week earlier than unsprayed controls.

If cool weather continues into early January, it will not be necessary to enhance flower bud induction. At that time, a GA spray may be advisable to reduce flowering in cultivars like mandarins. If cool weather is predicted to continue, I will discuss GA use next week.

Please email or phone if you have any questions albrigo@crec.ifas.ufl.edu or phone 863-956-1151).


12/19/2005

FLOWER BUD INDUCTION ADVISORY #4 for 2005-2006-12/19/05

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

Current Status:  Accumulated cool weather has now reached 600 to nearly 1050 hr < 68 degrees F. from southern to northern citrus districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be 110 to 140 additional hours below 68 degrees F. during the next 7 days. This means that all areas will be at least in the moderate-high range of flowering potential by next week. The cooler districts are in the high range, exceeding 900 hours. Some northern areas will reach the very high range by the end of this coming 8-day period. To view specific FAWN data for a location near you, 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 8-day forecast.

Up to now, cool temperature accumulation has been at a good, almost constant rate and is predicted to continue this week according to the NOAA 8-day forecast. One more week of cool weather after this week (until January 1 st ) will place all districts in an excellent position for heavy flowering if trees are healthy and had a moderate crop up to or after Hurricane Wilma. Rainfall has prevented soil moisture from depleting to provide drought conditions which could inhibit flower buds growth, but no extended warm period has occurred to cause an early bud growth problem.

See earlier advisories about planning for and using urea or PO3 sprays to enhance flowering. The need for using one of these sprays is greatly diminished. Growers may still want to consider using these sprays on weak (poor root system) or heavily bearing blocks, particularly in southern areas. If used, these sprays should be applied as the weather warms up at the first warm period, and you can have effective results until 3 or 4 days into the warm period. Usually, this provides a 7 day spray window for these applications. If cool temperatures last through the first week of January, it is much less likely that these sprays will be beneficial since a very good level of natural flower bud induction will have been reached.

With the high levels of induction hours that will have accumulated by Christmas, it is now time to worry about excessive flowering. Too many flowers in seedless cultivars (navels), hybrid blocks with a moderate to light crop and some strains of Rhode Red Valencia that set poorly result either in too much flower competition and poor set (navels and some Rhode Reds) or in excessive set (mandarin hybrids) and poor fruit size. A GA 3 spray is advised towards the end of the first warm spell that has 4 to 5 days exceeding 73 to 75 degrees F, note that these temperatures are now lower than stated previously because the intensity level of induction is now higher. The above cultivars are likely to have excessive flowering with few leaves associated with the inflorescence. GA 3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. Need for and best timing for a GA 3 spray in the various production zones will be assessed in coming advisories.

A new concern regarding winter management is the possibility of a freeze. Levels of cold hardiness are good now and should stay that way until a warm period occurs. This is an El Niño Neutral year, which increases the likelihood of a freeze. Generally, a hard freeze is most likely until we get pasted January 15 th to 20 th . If a warm period occurs before that date, some or all of cold hardiness will be lost if the buds start to swell and grow. Being able to apply drought stress is one way to prevent loss of cold hardiness. If winter rains stop and you keep soil moisture on the low side, you may benefit by shutting down irrigation if a warm period is predicted by a NOAA 8-day forecast.

The Web based Citrus Flowering Monitor System should be posted later this week. Check the CREC Homepage for an announcement and link to this tool perhaps by sometime tomorrow.

Please email or phone if you have any questions albrigo@crec.ifas.ufl.edu or phone 863-956-1151).


12/29/2005

FLOWER BUD INDUCTION ADVISORY #5 for 2005-2006-12/29/05

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

Current Status: Accumulated cool weather has now reached 800 to nearly 1300 hr < 68 degrees F. from southern to northern citrus districts, respectively. Also, the National Weather Service (NOAA) predicts that there will be 80 additional hours below 68 degrees F. during the next 7 days. This means that all areas will in the high to very high range of flowering potential by next week. The 8-day forecast has a warm period starting today. The NOAA forecast predicts 4 to 7 days of warm weather. To view specific FAWN data for a location near you, 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 8-day forecast.

Since all areas are at fairly high induction levels, this warm period should trigger differentiation of flower buds if soil moisture is adequate for growth. The flowering monitor system indicates that differentiation could have started in the Ona region. Except for Ft. Pierce , FAWN sites in citrus production areas have recorded only traces of rain over the past 14 days (FAWN), soil moisture may be depleted from lower rooting depths in most citrus producing area if restricted irrigation has been managed as we recommended earlier. If you stopped irrigation this week after using shallow irrigations in previous weeks, you may develop drought conditions for this warm period which could inhibit flower buds growth this week. This may be advisable if you want to maintain some cold hardiness for a potential freeze in mid-January or if you wish to delay bloom into mid to late March.

It is now time to worry about excessive flowering. Too many flowers in seedless cultivars (navels), hybrid blocks with a moderate to light crop and some strains of Rhode Red Valencia that set poorly result either in too much flower competition and poor set (navels and some Rhode Reds) or in excessive set (seedy mandarin hybrids) and poor fruit size. A GA 3 spray is advised towards the end of this first warm spell (4 to 5 days exceeding 75 degrees F), note that these temperatures are lower than stated previously because the intensity level of induction is now higher. The above citrus types are likely to have excessive flowering with few leaves associated with the inflorescence. GA 3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. The warm period will persist over New Year's weekend and GA sprays can be effective if used next week. Although flowering potential is probably high enough, if you plan to use either urea or PO3 to enhance flowering, you should apply those sprays immediately. Personally, I would try to slide through a possible warm period at this time by having my trees in drought stress. This is because of the chance of a hard freeze in January.

This is an El Niño Neutral year, which increases the likelihood of a freeze. Generally, a hard freeze is most likely until we get pasted January 15 th to 20 th . If a warm period occurs before that date, some or all of cold hardiness will be lost as the buds start to swell and grow. Being able to create drought stress is one way to prevent loss of cold hardiness. Since the chance of rain on Christmas day apparently occurred only in the Indian River, those who managed irrigation and have now shut down irrigation may prevent loss of cold hardiness over the New Years weekend.

The Web based Citrus Flowering Monitor System is now posted. The link to this tool is: http://orb.at.ufl.edu/DISC/bloom When the Window comes up, click on Run Model, fill in the site and other information and then click on the run model tab below this information. You should see a graph with black line indicating accumulated induction hours and a red line extension for the projected additional induction hours from the NOAA 8-day forecast. You can evaluate any site where FAWN has a weather station (The first pull down information window)

For the next 5 days, please email if you have any questions albrigo@crec.ifas.ufl.edu .


1/12/2006

FLOWER BUD INDUCTION ADVISORY #6 for 2005-2006-1/12/06

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

Current Status:  Accumulated cool weather reached 810 to 1250 hr < 68 degrees F. from southern to northern citrus districts, respectively, before the first warm period triggered differentiation of some flower buds starting about 22-27 December, depending on the citrus district. An additional 250 hours of cool weather accumulated before the second warm period that we are now experiencing. The NOAA 8-day forecast predicts cooler weather this weekend and then warming again next week. This should solidify the beginning of differentiation of most flower buds. Evidence of their swelling should be readily visible in the next two weeks, particularly terminal buds. To view specific FAWN data for a location near you, 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 8-day forecast.

Full bloom is predicted to be the first week of March, with a second wave of flowers by mid-March if most available buds were not induced by the Christmas warm period. If two flowering cohorts do occur, they probably will appear as a prolonged bloom over this two week period. Actual bloom date may change if abnormally warm (earlier bloom date) or cool (later bloom date) weather occurs.

On all healthy, non-hurricane damaged trees, flowering levels should be very good. Too many flowers in seedless cultivars (navels), hybrid blocks with a moderate to light crop and some strains of Rhode Red Valencia that set poorly results in too much flower competition and poor set (navels and some Rhode Reds). On the other hand, too many flowers usually results in excessive set and poor fruit size in seedy mandarin hybrids. A GA 3 spray is advised in these cases by early next week. GA 3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence.

Some growers may still be successfully managing soil moisture and have gotten through the Christmas and current warm periods with their trees under drought stress. When the 8-day forecast looks favorable for no freeze chance through January 25 th , it will be a good time to start irrigation and then to apply the first ground fertilizer for the year.

This is an El Niño Neutral year, which increases the likelihood of a freeze. Generally, a hard freeze is most likely until we get pasted January 15 th to 20 th . If a warm period occurs before that date, some or all of cold hardiness will be lost as the buds start to swell and grow. Being able to create drought stress is one way to prevent loss of cold hardiness.

The Web based Citrus Flowering Monitor System is now posted. The link to this tool is: http://orb.at.ufl.edu/DISC/bloom When the Window comes up, click on Run Model, fill in the site and other information and then click on the run model tab below this information. You should see a graph with a black line indicating accumulated induction hours and a red line extension for the projected additional induction hours from the NOAA 8-day forecast. The black to blue line moving downward with time indicates the progress of flower bud differentiation and bud development to a full bloom date on the x axis. You can evaluate any site where FAWN has a weather station (The first pull down information window), by going back one step to refresh the Run Model Window.

Please email or phone if you have any questions albrigo@crec.ifas.ufl.edu , 863-956-1151.