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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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11/11/2002

FLOWER BUD INDUCTION ADVISORY #1 for 2002-2003-11/11/02

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 

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.

It is the time of year to start following citrus flower bud induction conditions for the coming year's bloom. Cool weather stops growth and then promotes induction of flower buds as more cool weather accumulates. A warm spell can then initiate differentiation which after sufficient days of warm temperatures leads to bloom. The meteorologists say that this winter in Florida will be slightly cooler than normal, a weak El Nino year. Potentially, sufficient cool temperatures should accumulate, below 68 degrees F, to induce adequate flower buds for a good crop yield. Sufficient flower bud induction under Florida conditions is achieved when 850 to 1000 hours of accumulated cool temperatures < 68 degrees F occurs without interruption before a warm spell ( ie., 7 to 12 days with max. temperatures > 80 and min. temperatures >70 degrees F) triggers the beginning of bud growth. So far this year little cool weather has occurred to slow down or stop vegetative growth on mature trees, 150 to 175 hr < 68 degrees F in southern districts and 250 to 275 hr < 68 degree F in northern districts. This information is available on the Florida Automated Weather System as less than 65 and less than 70 degrees F (www.fawn.ifas.ufl.edu). A third cool spell of the Fall is predicted to start Wednesday or Thursday and continue for the following 5 or more days depending on location in the citrus growing areas ((www.crec.ifas.ufl.edu ), click on Research and Extension, then weather and 8 day forecast). The 8 day forecast from the National Weather Service predicts that our accumulated cool weather (below 68 degrees F) will be 275 to 320 hours in northern locations and 200 to 250 hours in southern locations 8 days from now.

The major concern for the next 60 days is the possibility of an early warm spell that will initiate differentiation of easily induced flower buds or push vegetative buds to grow. Some flower buds will be induced in the range of 300 to 600 accumulated hr < 68 degrees F. Warm events when only these levels of induction have occurred result in initiation of a weak flowering event, and therefore, many buds remain that can be induced by later cool spells resulting in multiple blooms occurring. When early winter bud break was not prevented in Florida (1963 to 2002 records), multiple blooms occurred in over half of the years. The time period in which a warm spell can lead to some bud growth and then result in multiple blooms is roughly Thanksgiving to Christmas. Extreme warm conditions existed last Fall and early Winter and resulted in the poor flowering and the low crop being experienced this year. Presently, the only management tool available to eliminate or reduce the chance of multiple blooms is to allow water stress to occur during these warm periods. The difficulty last year was that warm weather was continuous until December 18th. Allowing trees to be in water stress for this extended a period could lead to poor photosynthesis, little fruit growth or sugar accumulation and excessive fruit drop of the current crop, particularly for early maturing cultivars. If the warm spell(s) are of the more typical 7 to 10 day duration, mild water stress will have little impact on overall fruit development or quality. Mild water stress may be interpreted as leaf wilt observed by 10 or 11 am.

With the shallow root systems in bedded groves, it is relatively easy to reach sufficient stress to suppress growth by withholding irrigation for a few days. In deeper sandy soils, 2 or more weeks may be required for a fully saturated root zone to dry sufficiently for leaf water stress symptoms to appear. To minimize the time to initiate water stress, the soil should be allowed to dry out in late fall so that trees show wilt by mid-day. For bedded groves, minimum irrigation can then be applied as needed until a weather prediction indicates a warm spell is expected. At this time irrigation should be shut down. For deep sands, the soil needs to be dried out to wilt and then leave part of the lower root zone dry each irrigation until at least Christmas so that no growth can occur. This may be risky for Hamlin or other early maturing cultivars that tend to drop fruit near harvest.

If no rains interrupt a mild water stress condition of the citrus tree, buds will not grow in response to warm temperatures. Once a warm spell occurs and has passed with the trees under water stress, trees again can be watered to minimize fruit water stress. Although no weather prediction is guaranteed even by the meteorologist, rains in the winter usually come on the fronts of cool spells. Therefore, the chances of being able to apply water stress to prevent an early flower bud differentiation is reasonably good for most short duration warm spells. Each of this year's three cool spells, including the current predicted one, has had a rain prediction on the front of the cool spell.

The next few advisories will update accumulating weather effects on flower bud induction and provide timing information if water stress should be applied. As we reach appropriate moderate levels of flower bud induction, information concerning methods for enhancing or reducing flowering intensity (sprays of urea to enhance or GA3 to reduce) will be provided (see last years advisories for more information about these sprays). Much of what has been stated above has now been incorporated into a ‘Flowering Expert System for Florida Citrus'. Our new flowering decision support system (expert system) that is now in test with some growers will be discussed during two talks scheduled in the next two months. Factors controlling flowering, use of control strategies for stopping early flowering events, enhancing or diminishing flowering intensity and when to use these options will also be discussed. These two talks are November 12th at 11 am in the CREC Ben Hill Griffin Hall and on December 17th at 10 am in the La Belle, Collier County Extension Office Auditorium.



11/18/2002

FLOWER BUD INDUCTION ADVISORY #2 for 2002-2003-11/18/02

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 an update from the first advisory. Essentially all areas received heavy rains that saturated the root zone. However, a full week of cool temperatures are expected through next Monday, and therefore no bud growth will occur. Growers should follow the NOAA 8 day forecast (http://www.crec.ifas.ufl.edu/CRECHOME/crecweather.shtml) later in the week to see if a warm spell is predicted for next week. If so, sufficient cool temperatures will have accumulated that a weak initiation of flowering could start with the first significant warm spell. With a weak induction level, some apex buds may start to differentiate if sufficient soil moisture is present. Growers should allow trees to reach late morning wilt before starting to irrigate again. See last weeks advisory for general guidelines for irrigation depending on rooting depth after the current soil moisture is used by the trees.

Southern areas have accumulated about 200 hours below 68 degrees F and should reach the 300 mark by next Monday. Northern areas are at about 250 hours and should exceed 300 hours by next Monday.

Remember that the goal is to get to Christmas and/or above 900 hours below 68 degrees F before allowing initiation of flower bud differentiation. At that time flower bud enhancing sprays such as urea and increasing irrigation rate are appropriate. I will discuss those options in one or two weeks after we reach 600 hours below 68 degrees F.

Applying water stress for any warm spells that may occur before we reach those accumulated cool temperature goals, should minimize any early bud development and may also conserve freeze hardiness that the trees may have gained. At the same time, short periods of water stress (7 to 10 days) will have little adverse effects on fruit size or fruit droppage.

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


11/25/2002

FLOWER BUD INDUCTION ADVISORY #3 for 2003-2003-11/25/02

This is a further update on Florida weather conditions as they influence citrus flower bud induction. Most of the soil moisture in the root-zone from last week's heavy rains should now be dissipated. But irrigation should be used sparingly so that drought can be initiated by stopping irrigation if a warm spell occurs before Christmas. Another full week of cool temperatures is expected through next Monday, and therefore no potential for bud growth should occur this week. Growers should follow the NOAA 8 day forecast (http://www.crec.ifas.ufl.edu/CRECHOME/crecweather.shtml) later in the week to see if a warm spell is predicted for next week. If so, sufficient cool temperatures will have accumulated that a weak to low initiation of flowering could start with the first significant warm spell. With a low induction level, many apex buds may start to differentiate if sufficient soil moisture is present. Growers on deep sands should allow trees to reach mid-day wilt before starting to irrigate again. Trees in bedded groves should show wilt symptoms more quickly than those on deep sands. See the initial advisory for general guidelines for irrigation depending on rooting depth after the current soil moisture is used by the trees.

Southern areas have accumulated about 300 hours below 68 degrees F and should be above the 400 mark by next Monday. Northern areas are at about 350-400 hours and should exceed 450-500 hours by next Monday.

Remember that the goal is to get to Christmas and/or above 900 hours below 68 degrees F before allowing initiation of flower bud differentiation. At that time flower bud enhancing sprays such as urea and increasing irrigation rate are appropriate. I will discuss those options next week as we approach accumulation of 600 hours below 68 degrees F.

In the meantime, our goal is to stop irrigation before a warm spell occurs (7 to 10 days with highs above 80 degrees F and lows near 70 degrees). Stopping irrigation soon enough before the warm spell should allow water stress to develop before the warm spell which will minimize any early bud development. In addition to stopping bud development, drought stress may also conserve freeze hardiness that the trees have gained during the current flower bud induction period.

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


12/2/2002

FLOWER BUD INDUCTION ADVISORY #4 for 2002-2003-12/2/02

Florida weather conditions continue to favorable this year for good citrus flower bud induction.

Southern areas will have accumulated about 500 hours below 68 degrees F by next Monday. Northern areas should have exceeded 600 hours by next Monday. Remember that the goal is to get to Christmas and/or above 900 hours below 68 degrees F before allowing initiation of flower bud differentiation.

Irrigation should be used sparingly until Christmas so that drought can be initiated by stopping irrigation if a warm spell occurs before then. Although 2 warm days are expected, Tuesday and Wednesday, this coming week should have generally cool temperatures, and therefore no potential for bud growth should occur this week. Growers should follow the NOAA 8 day forecast (http://www.crec.ifas.ufl.edu/CRECHOME/crecweather.shtml) later in the week to see if a warm spell is predicted for next week. If so, sufficient cool temperatures will have accumulated that a low to low-moderate initiation of flowering could start with the first significant warm spell. I would expect the first 2 or 3 buds from the shoot apex would start to differentiate if sufficient soil moisture is present during any warm spell that might occur from now until Christmas. Growers on deep sands should allow trees to reach mid-day wilt before irrigating, using perhaps 2 irrigations per week of about one hour duration. Trees in bedded groves should show wilt symptoms more quickly than those on deep sands and be irrigated accordingly, but sparingly.

Our goal, until Christmas, is to stop irrigation before a warm spell occurs (7 to 10 days with highs above 80 degrees F and lows near 70 degrees). Stopping irrigation soon enough before the warm spell should allow water stress to develop before the warm spell which will minimize any early bud development. In addition to stopping bud development, drought stress may also conserve freeze hardiness that the trees have gained during the current flower bud induction period. Another advantage of avoiding the initiation of early flower bud differentiation (the start of a bloom event) is that this will delay bloom date. For processed oranges this later bloom date should result in higher acidity levels in the Fall so that normal harvest dates can be reached with good Brix/acid ratios.

If a warm spell occurs around Christmas or when about 900 hours below 68 degrees F have accumulated, flower bud enhancing sprays such as urea or PO3 are appropriate to apply followed by increasing irrigation rates to stimulate growth. Minimum rates for urea should be 25 lbs N per acre (28 lbs is preferred, 63 lbs urea). PO3 materials may be applied at 2.5 qts/acre of a 26-28 % product. Such sprays, especially urea, will usually advance bloom date about one week. The best timing should be just before the predicted warm spell and not later than a couple of days into the warm spell. These sprays can be applied with good aerial application or by ground in 30 to 125 gal/acre.

If the bloom intensity potential is high when a warm spell causes initiation of flower bud differentiation, then a gibberellin spray (20 oz per acre of 4 % GA) may be appropriate to minimize the flowers per inflorescence in order to get a leafy bloom with stronger ovaries. This is primarily important for seedless cultivars in any year and mandarin hybrid types that are coming into the on-year of an alternate bearing cycle. GA should be applied at the end of the warm spell rather than before as recommended for urea. An early winter GA spray could stimulate shoot growth of the swelling buds if another warm spell comes soon. These buds or young shoots would then be much more susceptible to a freeze. If we can get to Christmas without a warm spell, then this hazard is not an issue. GA should be applied in 100 to 200 gal/acre total spray volume.

For those interested in applying either urea for Valencia or other processing oranges or GA for seedless cultivars or mandarins, materials should be purchased now and spraying equipment maintenance taken care of or custom spraying needs to be contracted.

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


12/9/2002

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #5 for 2002-2003-12/9/02

Warning - The next 5 days will be relatively warm (low 80s) particularly across the southern half of the citrus zone. Although it may not be warm enough to initiate flower bud induction, the predictions are too close to initiating temperatures to take chances. It would be advisable to stop irrigating, if you haven't already, and allow some water stress to develop so that no growth is initiated at this time. The daily highs in the northern areas are predicted to be in the mid 70s. It appears that temperatures will get cooler again at the end of the week. If temperatures do cool off for a sustained period, look at 8 day forecast, then moderate irrigation can be resumed at the end of the week.

To date we have accumulated about 550 hours of inductive temperatures in the southern zones and over 600 in the northern-most zones. With the relatively warm week predicted, we will only accumulate another 100 hours this coming week. It would be desirable to accumulate another 200 to 300 hours after that before allowing the trees to initiate flower bud development. That should be accomplished by Christmas or New Years.

Until then, keep your eyes on the weather for warm spells and now also for freezes. Hopefully, we will not see one of those.

The next advisory should be posted early on Monday, 16 Dec. I may be late with the one following that, so watch the weather carefully on your own.

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



12/16/2002

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #6 for 2002-2003-12/16/02

First the bad news - So much for my hoping you could develop some water stress by withholding irrigation. If anything, some of you may have been experiencing flooding conditions with all the rain. Now the good news - Temperatures were not as warm as predicted even in the southern half of the citrus zone. It appears, from our model, that initiating temperatures did not occur. The next 8 days should be satisfactory for continuation of inductive temperature accumulating, without sufficient warm weather to cause the beginning of bud break. The southern part of the industry should experience not more than 2 or 3 days near 80 and then it should become slightly cooler by next weekend.

To date we have accumulated about 600 hours of inductive temperatures in the southern zones and over 750 in the northern-most zones. With the predicted temperatures for the coming week, we should reach inductive temperature accumulations of 650 to 700 hours in southern areas and 800 to 850 in northern area by the end of the coming week. If the following week (Christmas) remains cool, northern areas should exceed 900 hours while southern areas should reach 800 accumulated hours below 68 degrees F. If a significant warm spell does not occur by New Year's day, trees should be in excellent condition to push into flowering at the first warm spell after that.

At that time, growers of processed oranges should consider whether to push their trees or try to hold them back for another 2 to 3 weeks. If additional rainfall does not prevent the ability to develop some water stress, growers should test the effect of withholding irrigation in order to get by an early January warm spell and then push their trees with irrigation at the time of the next warm spell.

Growers should be prepared to apply urea or PO3 just before the start of the first significant warm spell if soil moisture continues to be plentiful and there is no possibility of preventing bud break by developing some water stress. Previous experience indicates that flowering enhancement and increased yields can be obtained by applying either product after 850 to 900 hours of cool temperatures have accumulated.

Look for another update on Monday or Tuesday of next week.

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


12/22/2002

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #7 for 2002-2003-12/22/02

This week, we have another 4 to 5 days with relatively warm (high 70s to low 80s) temperatures predicted for the southern half of the citrus zone. Like 2 weeks ago, it may not be warm enough to initiate flower bud differentiation, but it would be desirable to allow some water stress to develop so that no growth is initiated at this time. This assumes that little rain has fallen since week before last. There is a chance of rain predicted, but hopefully any rain will be towards the end of this warm spell. The high in the northern areas is predicted to be near 80 for one day only. These temperatures should not initiate flower bud differentiation. It appears that temperatures will get cooler again at the end of the week, but watch the weather forecasts.

To date we have accumulated about 720-740 hours of inductive temperatures in the southern zones, about 850 hours in central areas and 900 in the northern-most zones. Based on predicted temperatures, we should reach 800, 830 and 1000 hours in the southern, central and northern areas this coming week. At that time we will have acceptable flower bud induction levels in all but the southern areas, but it would be best if another week or two of cool weather occurred in all areas so that bloom date would be later in March.

For those planning to use urea or PO3 sprays on processing orange blocks, you should prepare to do that as soon as the next warm spell occurs and before mid-January. However, since most blocks have a light crop and induction levels are likely to exceed 1000 hours, good flowering should be expected whether you use flower enhancing sprays or not. Remember that these sprays, if used, need to be applied before the warm weather has occurred. Follow the NOAA 8 day forecasts linked to this website for prediction of the warm spell.

For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray may be useful at the end of the next warm spell that has 4 to 5 days exceeding 82+ degrees. These cultivars are likely to have excessive flowering with few leaves associated with the inflorescence. GA3 sprays should reduce the amount of flowering and increase the leaves in each inflorescence. Best timing for this sprays will be assessed as we see what temperatures are predicted each week.

See the next advisory before the new year.

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


12/29/2002

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #8 for 2002-2003-12/29/02

This week, we have another 3 to 4 days with relatively warm (high 70s to low 80s) temperatures predicted for the southern half of the citrus zone. Again, it may not be warm enough to initiate flower bud differentiation, but our model predicts that a bloom may have been initiated in some districts. With the increased level of induction that now exists, it would be desirable to allow some water stress to develop, particularly in the southern areas, so that no growth is initiated at this time. This assumes that little rain has fallen. If it is not possible to develop some water stress, urea or PO3 sprays are recommended this following week in the southern areas. The high in the northern areas again is predicted to be near 80 for one day only. These temperatures should not initiate flower bud differentiation. It appears that temperatures will get cooler again at the end of the week, but watch the weather forecasts.

To date we have accumulated about 800 hours of inductive temperatures in the southern zones, about 1000 hours in central areas and 1050 in the northern-most zones. Based on predicted temperatures, we should reach 900, 1050 and 1100 hours in the southern, central and northern areas this coming week. We will have acceptable flower bud induction levels in all areas, but it would be best if another week of cool weather occurred in all areas, particularly the southern regions, so that bloom intensity will be a little higher and bloom date will be later in March.

For those planning to use urea or PO3 sprays on processing orange blocks, you should prepare to do that as soon as the next warm spell is predicted and before mid-January. However, since most blocks have a light crop and induction levels are now approaching or exceeding 1000 hours, good flowering should be expected whether you use flower enhancing sprays or not. Remember that these sprays, if used, need to be applied before the warm weather has occurred. Follow the NOAA 8 day forecasts linked to this website for prediction of the warm spell.

Since our model predicts that initiation of a bloom may have started in one or two locations, urea or PO3 sprays may be particularly beneficial in the southern areas. With induction levels near 1000 hours and if temperatures exceed the predicted (3 or 4 days near 80 degrees) this week, initiation of flower bud differentiation is likely to occur. The week following New Year's Day will be a good week to spray if you intend to. This is particularly important if the 8 day forecast indicates warm weather next week.

For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray may be useful at the end of the next warm spell that has 4 to 5 days exceeding 82+ degrees. These cultivars are likely to have excessive flowering with few leaves associated with the inflorescence. GA3 sprays should reduce the amount of flowering and increase the leaves in each inflorescence. Best timing for this sprays will be assessed as we see what temperatures are predicted each week. This coming week does not appear to be warm enough to consider GA sprays yet, but again if temperatures exceed predicted in southern areas then next week may be a suitable time.

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


1/5/2003

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #9 for 2002-2003-1/5/03

This week, we have cool (highs <70s) temperatures predicted for all of the citrus zones. It should not be warm enough to initiate flower bud differentiation. Late in the week, high temperatures may reach the low 70s in the southern areas, but generally it will be too cold to get good uptake of either urea or PO3 sprays this week.

To date we have accumulated in excess of 900 hours of inductive temperatures in the southern zones, above 1100 hours in central areas and over 1200 hours in the northern-most zones. Based on predicted temperatures, we should reach 1050, 1230 and 1300 hours in the southern, central and northern areas this coming week. We will have acceptable flower bud induction levels in all areas at the end of this week.

As stated last week, our model predicts that initiation of a bloom has started in one or two locations. The predicted date of initiation of differentiation was 18 to 20 December with a predicted bloom date of 5 to 7 March. I also advised that urea or PO3 sprays might be applied to processing orange blocks with good crops in the southern areas if warm weather occurred. If those sprays were not applied, it will probably be too cold this week to apply foliar sprays. There is a long term forecast for a change in the jet stream and likelihood of colder weather after January 11th. If that occurs, no flower enhancement sprays are warranted. If, however, temperatures warm up next week, blocks with current heavy crops may still benefit from a spray.

For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray is advised at the end of the next warm spell that has 4 to 5 days exceeding 78 to 80 degrees. These cultivars are likely to have excessive flowering with few leaves associated with the inflorescence. GA3 sprays should reduce the amount of flowering and increase the leaves in each inflorescence. Best timing for this sprays will be assessed as we see what temperatures are predicted each week. This coming week will not be warm enough to consider GA sprays at this time.

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


1/17/2003

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #11 for 2002-2003-1/17/03

All areas now have had initiation of some flower bud differentiation. Our model still indicates that only one flowering wave of buds has started to push. It takes the model about 7 to 9 days to evaluate a warm temperature event and decide if it was sufficient to push (initiate) some buds to start growth. We probably still have 80 % of the potential flowering buds to be initiated, but some more may have been pushed this past week in the southern citrus areas.

This week, we have cold temperatures predicted for all of the citrus zones over the weekend, but the southern areas will have 5 days with highs in the 70s with 3 or 4 days in the mid-70s. These temperatures, if they occur, should start the bulk of the remaining flower buds to initiate growth. The duration of higher temperatures in the northern half of the citrus area will be only 2-3 days in the lower 70s and 2 days in the high 60s. This will be a good time to apply either urea or PO3 sprays in the northern areas if you were planning to do so. Again, the most likely blocks to benefit are those with heavy current crops and especially Valencias with a good crop. For central and north Florida, the predicted temperatures may initiate flower bud differentiation since the flower bud induction levels are so high.

To date we have accumulated in excess of 1150 hours of inductive temperatures in the southern zones, above 1350 hours in central areas and over 1400 hours in the northern-most zones. Based on predicted temperatures, we should reach 1300, 1500 and over 1600 hours in the southern, central and northern areas this coming week. We will have excellent flower bud induction levels in the southern areas and perhaps excessive levels (snowball bloom potential) in all other areas at the end of this week.

For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray is advised at the end of the next warm spell that has 4 to 5 days exceeding 73 degrees. These conditions should be met this coming week in southern areas if predicted temperatures occur. The above cultivars are likely to have excessive flowering with few leaves associated with the inflorescence. GA3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. Best timing for this sprays in central and northern zones will be assessed as we see what temperatures are predicted each week. We will report an assessment of appropriateness for this spray in the northern area on Friday of next week.

For those growers testing our flower bud induction intensity-bloom date model, you may find that the current version will not provide a second initiation of differentiation to bloom curve for northern areas or central areas that exceed 1500 hours of cool inductive temperatures. This is a programming problem because we did not anticipate inductive levels exceeding 1500 hours while there were still flower buds to have growth initiated. We are working on a patch that may be provided or discussed in these advisories. We will provide information about the second wave of flower bud growth for these areas one way or another.

Lets be bold. I predict that the minimum temperatures tomorrow morning likely will not reach the predicted lows. Although the jetstream dipped more strongly from North to South through the Midwest towards Texas yesterday, it has apparently stabilized so that air flow will continue to be mostly lateral, West to East, across the Gulf of Mexico. This should continue to moderate temperatures reaching Central and Southern Florida. Another good sign is that temperatures in the central to northern citrus stopped dropping about 11 am to noon and were holding fairly steady through 2 pm. Lets keep our fingers crossed.

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


1/24/2003

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #12 for 2002-2003-1/24/03

FREEZE ON FRIDAY - Temperatures generally were in the upper 20s to low30s. Most of the tree can withstand a short period at these temperatures after the cold weather that the trees have been subjected to. We don't know about the buds that have already started to swell. We rechecked on terminal buds at Lake Alfred yesterday. They now show that about 50 to 70 % of the terminal 3 buds had some swelling indicating start of growth. This compares to 10 to 20 % of these buds showing some bud swell when they were checked 2 weeks ago. Many of the buds in these shoot positions had enough additional growth from 2 weeks ago that they could be seen without use of a hand lens. We don't know how susceptible these buds were to freezing temperatures compared to the shoots and trees in general, which should have withstood temperatures as low as 21 to 22 degrees F. We will check some of these swollen type buds on Monday or Tuesday from more northern sites near Avalon and Tavares.

All areas now have had considerable initiation of some flower bud differentiation. Our model indicates this and shoot terminal bud examinations confirm this. Because of the very high accumulated cool temperature hours, many more buds down the spring and summer shoots than the first 3 buds on spring or summer shoots will be flower buds. If the projected warm spell projected for the end of next week extends for 3 or 4 days, many of these buds should start to grow (swell). That should constitute our second major wave of initiation of flower bud differentiation.

Later next week while temperatures in central and northern Florida are in the low to mid-70s will probably be a good time to get reasonable uptake of either urea or PO3 sprays. Again, the most likely blocks to benefit are those with heavy current crops and especially Valencias with a good crop. But remember that the very high levels of induction in central and northern areas reduces the likelihood that these sprays will provide a benefit this year.

To date we have accumulated in excess of 1300 hours of inductive temperatures in the southern zones, above 1500 hours in central areas and over 1600 hours in the northern-most zones. These are very high levels of induction for Florida before the initiation of a second flower bud differentiation wave. Weather forecasts make it likely that at least another cool week will occur raising those levels even higher.

For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray is advised at the end of the next warm spell that has 4 to 5 days exceeding 69 to 72 degrees, note that these temperatures are now lower than stated previously because the intensity level of induction is now higher. These conditions may be met this coming week in northern as well as southern areas. The above cultivars will have excessive flowering with few leaves associated with the inflorescence. GA3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. Best timing for this sprays in all areas will be after next week if temperatures are as high as predicted for the end of next week and these temperatures continue for 4 or 5 days. We will confirm that conditions are adequate to apply a GA spray at the end of next week.

For those testing our induction-flowering date model, we are just getting the model updated for the high induction levels being experienced. In any area that shows more than 1500 hours of temperatures less than 68 degrees F, the current version will not show the next and final initiation of flower bud differentiation along with the projected bloom date. Hopefully, we will have an adjusted version to download early next week. Alternatively, I will report those conditions and projected bloom dates for the major areas.

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


1/31/2003

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #13 for 2002-2003-1/31/03

REMINDER TO ALL RIDGE CITRUS GROWERS - NITRATE BMP PROGRAM - The permanent rules are now in place for the voluntary program administered by the FDACS Office of Water Policy. Even if you were signed up for the interim measure, you have to sign-up again in order to qualify for the liability exemption provided by the program. All of the information is available on the DACS Website of the Office of Water Policy, which is listed in the links provide by this Website (http://www.floridaagwaterpolicy.com/ ).

All initiation of flower bud differentiation should be complete during this warm spell. Because of the very high accumulated cool temperature hours and this significant warm spell, all remaining buds on last year's spring and summer flush that can be expected to be flower buds will have initiated growth now. This second wave of flower bud differentiation may not be as large as the first wave that was initiated in late December. A report from Ft. Pierce-Vero Beach indicates that as many as 6 buds down the shoot are already swelling from new growth. In a heavy flowering year, 8 or 9 buds down the shoot might be expected to become flower buds.To date we have accumulated in excess of 1500 hours of inductive temperatures in the southern zones, above 1700 hours in central areas and over 1850 hours in the northern-most zones. These are very high levels of induction for Florida before the initiation of a second flower bud differentiation wave.

For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray is advised Monday to Wednesday next week. The above cultivars will have excessive flowering with few leaves associated with the inflorescence. GA3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. As stated previously, the use of urea or PO3 to increase flowering is probably not necessary this year on even fairly heavily cropped blocks.

For those testing our induction-flowering date model, we expect to have the model updated late today for the high induction levels being experienced. In any area that shows more than 1500 accumulated hours of temperatures less than 68 degrees F, the current version will not show the now occurring and final initiation of flower bud differentiation along with the projected bloom date. Hopefully, we will have the adjusted version ready to download early next week. Alternatively, I will report those conditions and projected bloom dates for the major areas in a new advisory early next week. My guess is that we will have a major bloom wave peaking the first week of March and a smaller, second wave peaking the 4th week of March. We will see what the model says next week.

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


2/4/2003

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #13 for 2002-2003-2/4/03

Initiation of flower bud differentiation for second flowering wave is completed during this warm spell. The intensity of the second wave of flowers will be fairly heavy. Flowering in the first wave, full bloom projected to be 5 to 10 March, will be primarily in the first 3 to 5 terminal bud positions, while the second wave, full bloom projected to be last week of March, will be in the 4 to 8th or 9th bud positions. I expect flowering into these bud positions because of the high accumulations of hours less than 68 degrees F. Counts of growing buds from Hamlin trees near Clermont had 60 % or more buds not growing in positions 2 through 8 in samples taken on 1/31, just as the second wave of bud growth was starting. These samples taken after the freeze has some bud edges singed, but all buds were still healthy. In a lower central flatwoods citrus area, Hamlin buds from a sampled grove had fewer buds showing any growth than the Clermont grove. On the other hand, Valencia trees at this same site had more buds growing (60 % of first 2 buds and about 40 % of 3rd bud position). Even so, there are still more buds that should produce flowers than were started in the first wave.

At the time of initiation of differentiation in the second wave of buds, there were 1250 to 1290 hours accumulated in the southern zones, above 1500 hours in central areas and over 1700 hours in the northern-most zones. These are very high levels of induction for Florida before the initiation of a second flower bud differentiation wave.

For seedless cultivars, hybrid blocks with a light crop and some strains of Rhode Red Valencia that set poorly, a GA3 spray was advised for this week. The above cultivars will have excessive flowering with few leaves associated with the inflorescence. GA3 sprays (20 oz per acre) should reduce the amount of flowering and increase the leaves in each inflorescence. As stated previously, the use of urea or PO3 to increase flowering is probably not necessary this year on even fairly heavily cropped blocks. Also, it is probably too late to apply these products for flowering enhancement now.

Our induction-flowering date model is working again. Although it does not give the cool hours accumulated above 1500, it does project the second wave of initiation and predicts flowering dates. Cooperators should receive a CD with the revised program or information to a download site. The projected bloom dates by location as of now are: Tavares-3/19 & 4/4, Avalon-3/3 & 4/3, Lake Alfred-3/7 & 3/31, Ona-3/6 & 3/24, Ft. Pierce-3/12 & 3/29, Immokalee-3/11 & 3/30.

We would appreciate if everyone that is following these advisories would observe and report the average full bloom date(s) of their cultivars with information about location. How close are these projections to actual bloom dates that occur? Also, please report, if 2 bloom waves are observed, generally which buds on the shoots contributed flowers to each wave or if different parts of trees or different trees contributed to the early March and late March waves.

We will start spacing these advisories out to once every two weeks until bloom, with mostly reports of flower bud growth. If anyone observes a general bloom earlier than the first week in March, please let me know. This will help us to make corrections, if needed, for various factors in the bloom date prediction model. Watch for possible cold temperatures next week.

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


2/21/03

FLOWER BUD INDUCTION AND SPRAY TIMING ADVISORY #15 for 2002-2003-2/21/03

Estimated dates of full bloom

Our model predicts that full bloom for a first wave of bloom should be around March 8-9 in southern areas, March 3-4 in central areas and March15-18 in northern areas for round oranges. The model fits the data used to develop it within + or - 5 days. The model predicts that a second wave of flower buds should reach full bloom near the end of March. It appears on many trees that this second wave may have many fewer flower buds involved in it, since so many buds are pushing now. Observations in this area suggest that bloom dates might be a little ahead of the estimate. Hamlins and Valencias have terminal flowers at small pop-corn and lots of pin-head visible. Mandarins are clearly behind these in stage of development, as expected. Some weak trees in the Ft. Pierce area were in full bloom on Wednesday, but other trees were perhaps a week to 10 days from full bloom. I would appreciate observations of full bloom dates on healthy trees from anyone making those observations. Please email to: albrigo@crec.ifas.ufl.edu . Indicate the cultivar and general location of the grove with your estimate of full bloom date.. This will help us in fine tuning the model if needed.

Early bloom foliar nutritional sprays

The few blocks I have looked at have mostly mixed inflorescences with a good number of leaves and flowers. These have a better chance to set fruit than flower buds with only flowers. On the other hand we expect heavy flowering so a lot of competition should occur and foliar nutritional sprays may help to improve fruit set. For those planning to put on an early bloom foliar nutritional spray, we recommend application at 5 to 10 % open flowers. That may occur next week. If you have several blocks to spray, you may need to start early next week and perhaps finish in full bloom. Consider that mandarin blocks will bloom last and navels usually bloom a little earlier than other oranges in trying to develop the best schedule.

A number of people observed accelerated older leaf drop and some additional twig dieback when 2 to 2.5 qts of any of the PO3 products were mixed with KNO3 or other N-P-K products last bloom period. Until we know more about these tank mixes, it may be better to use either PO3 with low levels of other nutritionals at bloom or a traditional foliar N-P-K mix at 10 to 15 lbs of N/acre. No phytotoxicity problems were observed when PO3 products and KNO3 at 10 to 15 lbs per acre when applied at the postbloom timing.

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


 

3/27/2003

FLOWER BUD INDUCTION ADVISORY #16 for 2002-2003-3/27/03

POST-BLOOM UPDATE - Estimating dates of full bloom

Our flower induction-bloom date model first predicted that the full bloom date for a first wave of flowers would be March 12-13 in southern areas, March 6-7 in central areas and March15-18 in northern areas for round oranges. The model predicted that a second wave of flower buds should reach full bloom near the end of March. As the flower bud development progressed into early February, the program moved the predicted dates of bloom up about 5 or 6 days so that central areas were expected to be in full bloom about March 1st. Our observations around this area put the actual bloom dates closer to the original 6 to 10 March prediction. Southern area trees bloomed a little behind the central ridge as predicted. While some weak trees bloomed early, most trees were closer to the original predicted dates. We will have to observe flowering dates for a couple more years and compare these to predictions before we can conclude how accurate the program is. Last year, the predicted dates appeared to be very close to the actual dates and this year's predictions were still within a week.

For all of the citrus areas in the state, most available buds initiated differentiation and reached full bloom in the first flowering wave. This left almost no buds to respond to the second warm spell for a bloom in late March. I did see some branches and one tree in a Valencia block in Avon Park that had a noticeable amount of the second bloom. In south Florida near Immokalee, I saw groups of trees within some blocks that had mostly the second bloom wave and were in full bloom. These were the zones of poorest soil and may have been drought stressed during the first initiating warm spell in late December due to low available soil moisture at that time. Other than these cases, every other block or report has been of almost exclusive first wave flowering.

Flowering progressed rapidly by all reports and observations. Up to 15 bud positions had inflorescences on strong summer shoots. Most inflorescences had a few flowers with several leaves. The good balance of new leaves with the flowers was probably because the first wave of flowering was initiated to differentiate after about 840 hours of cool temperature accumulation rather than the 1300 or so that had accumulated by the second warm spell. At that later time, mostly generative inflorescences, without leaves, should have been produced. This was observed March 26th in the trees on poorer soil that had mostly the second wave of flowering.

So far, so good on development of the new crop. There was a good bloom with a good ratio of leaves to flowers. No one has reported any significant PFD in spite of rains during bloom. Weather during flowering and the first drop wave has been fairly cool with good soil moisture levels thanks to the rains. In general we should have large fruitlet numbers going into the later drop period. This will result in a heavier than normal May-June drop, but there should be more fruitlets remaining after that than usual. The one negative factor so far is that bee activity on citrus flowers was lower than expected. It may be that nectar levels or sugar concentration were lower than normal. Unfortunately, we were not monitoring these factors this year. Watch particularly for heavy drop of fruitlets the next 3 weeks in hybrids that require cross pollination. This would indicate that poor pollination and ovary fertilization occurred.

Last year at bloom, many people observed phytotoxicity from sprays combining PO3 with KNO3 and sometimes other products. We have done a test this year to see if the same susceptibility existed. We included a PO3 rate that was half again as much as recommended (3 lbs per acre rather than 2). Only a slight amount of burn was observed and this occurred only at the excess rate ( three lbs PO3/ac) and when KNO3 with or without urea was added to the spray mix. It appears that last year's sensitivity was a one year occurrence, but we are not sure why it happened. No sensitivity occurred last year when similar sprays were applied post-bloom.

I would appreciate observations of full bloom dates on healthy trees from anyone making those observations. Please email to: albrigo@crec.ifas.ufl.edu . Indicate the cultivar and general location of the grove with your estimate of full bloom date.. This will help us in fine tuning the model if needed.