Upcoming Pest Events | Trap Catches | Insects | Diseases

Upcoming Pest Events | Trap Catches | Insects | Diseases

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Upcoming Pest Events | Trap Catches | Insects | Diseases

Geneva Predictions:
Codling Moth
Codling moth development as of August 21: 2nd generation adult emergence at 98% and 2nd generation egg hatch at 85%.

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Insect model degree day accumulations:

DD45 since 1st Oriental Fruit Moth 2nd generation catch, July 5 (100% egg hatch @ 1235-1260):
APPLETON: 1109
KNOWLESVILLE: 1123
SODUS: 1035
WILLIAMSON: 1086

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Upcoming Pest Events | Trap Catches | Insects | Diseases

    Flyspeck disease on apples continued to cause problems for some New York and New England apple growers in 2005.  Last summer I published an article reviewing our current understanding of flyspeck development in northeastern United States (Scaffolds Fruit Journal 14[14], 20 June 2005; http://www.nysaes.cornell.edu/ent/scaffolds/2005/050620.html).  To summarize, flyspeck ascospore release begins about the time that apple trees reach petal fall.  Ascospores are relatively unimportant in sprayed orchards because scab fungicides prevent infections, but the ascospores initiate new infections on wild hosts in the orchard perimeters.  After 270 hr of accumulated wetting, counting from petal fall (hr-awpf), primary infections initiated by ascospores on wild hosts begin releasing conidia that blow into orchards, where they can initiate infections on apple fruit.  Another 270 hr of accumulated wetting (hr-aw) is required before the flyspeck becomes visible on fruit.  We have documented repeatedly over the past five years that flyspeck incidence on fruit left unprotected after early June increases rapidly soon after we reach 540 hr-awpf.  Dew periods must be included in calculations of hr-aw, and in some years dews contribute a significant number of wetting hours during August and September. 

   In the article cited above and in previous extension articles, I have suggested that Topsin M, Sovran, Flint, and Pristine would eradicate flyspeck infections on apple fruit that had not yet accumulated more than 100 of the 270 hr-aw required for lesion development on fruit.  That recommendation was based on my interpretation of previous field trials, and it meant that adequate flyspeck control should be expected if the first summer fungicide spray was applied anytime between 270 and 370 hr-awpf.  Unfortunately, research conducted in 2005 suggests that our model for spray timing needs some revisions.  The details of the 2005 trial have been published (see citation at the end of this article) and will not be repeated here, but the resulting changes in our understanding of flyspeck are outlined below.  Those who want only the practical recommendations without the confusing details can skip directly to the last section of this article.

Revised understanding of fungicide activity against flyspeck

   Our 2005 field trial provided evidence that none of our apple fungicides truly eradicate pre-existing flyspeck infections.  Instead, the fungicides appear to arrest fungal growth, thereby extending the incubation period for flyspeck.  Infections initiated in late June or early July before the first summer fungicide is applied may become “quiescent” until fungicide residues drop below the levels required to suppress fungal growth.  As fungicide residues dissipate during the interval between the last spray and harvest, some of these suppressed colonies can begin growing again and then appear on fruit prior to harvest, even when there is less than 270 hr-aw between the presumed end of fungicide protection and the time that fruit are harvested.

   As an example, consider a hypothetical case where the first summer fungicide was applied at 370 hr-awpf.  Some of the earliest flyspeck infections in that orchard would have a 100 hr “head start” toward the 270 hr-aw required for disease appearance.  If fungicide coverage was maintained throughout the rest of the summer, those early infections would remain suppressed right up through harvest.  However, if a heavy rain (more than 2 inches rainfall) occurred on 1 Sept. and removed all fungicide residues, then the suppressed flyspeck infections could resume growth and might appear after only 170 hr of additional wetting, counting from the end of the 1 Sept. rain event in this example.

      If fungicides suppress but do not eradicate pre-existing flyspeck infections, then we must grapple with other unresolved issues.  Do suppressed lesions really take off again where they left off as I’ve suggested in the example in the previous paragraph, or does post-infection application of fungicides set back lesion growth so that more than 270 hr-aw (pre-spray hours plus end-of-season hours) are required before the disease appears on fruit?  Do weather conditions following post-infection fungicide sprays affect survival of flyspeck infections?  How can we estimate when suppressed flyspeck colonies resume growth, since we have no accurate means of assessing when fungicide residues on fruit surfaces drop below suppressive levels?  I don’t have answers to these questions, but the answers may not be essential for designing control programs on a practical level.

Revised spray-timing recommendations for controlling flyspeck

   Given all of the evidence available to date, a conservative approach to controlling flyspeck can be outlined as follows: 

1. Fungicide protection against flyspeck should be initiated beginning at 270 hr-awpf and should be maintained until close to harvest, with fungicide coverage being renewed every 21 days or after 2 inches of accumulated rainfall, whichever comes first.
   
2. The 270 hr-aw incubation period for flyspeck on fruit can be viewed as a cumulative “grace period” for absence of fungicide coverage during the growing season.  If the first spray during summer is delayed to 370 hr-awpf (thereby using up 100 hr of the grace period), that may reduce the preharvest “grace period” to only 170 hr-aw for the period after fall rains remove fungicide protection prior to harvest. 
   
3. Growers who fill large storage rooms rapidly during harvest should recognize that flyspeck can continue to develop on warm fruit after harvest if fruit are wet.  I have no detailed data on flyspeck development during storage, but I would guess that 70 hr of the 270-hr incubation period might be completed after harvest in storage rooms, where high humidity and fluctuating temperatures caused by the addition of warm fruit each day can result in condensation on cooled fruit from previous harvests.  Growth of flyspeck on harvested fruit would cease as soon as fruit surface temperatures in the middle of the stack drop below the limiting temperature for flyspeck incubation, but I’m not certain what that temperature is (perhaps 45°F?).  If fruit remain wet and warm after harvest, then the grace period for accumulated wetting during the growing season might be only 200 hr because some of the grace period must be reserved for postharvest disease development.  Again, we have no experimental evidence pro or con, but I suspect that postharvest fungicide drenches will suppress flyspeck development in storage.  If that is true, then the full 270-hr-aw grace period would be available preharvest for fruit that will receive postharvest fungicide treatments.

Practical suggestions for late-summer control of flyspeck

   The bottom line is that in years favorable for flyspeck development, we can take fewer risks (i.e., we need tighter summer fungicide programs) than we had previously supposed.  In hot, dry seasons, one or two fungicide sprays will still provide complete control of flyspeck, but in wet years a final fungicide spray will be needed in September for varieties that will be harvested after September 20. 

   Severity of flyspeck in any given year may be influenced by the weather conditions the previous year because wet summer/fall seasons will give rise to more over-wintering inoculum in wild hosts.  The higher inoculum levels will result in greater disease pressure the following year.  Wet summers also give rise to situations during the growing season where fruit are unprotected due to fungicide wash-offs from thunderstorms or other rain events.  Those intermittent periods without fungicide protection are of little consequence in years with dry September weather, because they generally will not exceed the 270-hr-aw grace period required for signs of flyspeck to appear on fruit.  In a wet September, however, the cumulative effect of intermittent lapses during the growing season plus preharvest wash-off of fungicides can result in significant losses to flyspeck if no sprays are applied in September.

   Decisions on if and when to apply a September spray should be made after careful consideration of numerous factors:

1. Did the orchard in question have consistent fungicide coverage from 270 hr-awpf up through August, or were there significant periods where flyspeck infections could have been initiated during summer?  In a year when July and August are hot and dry, even a modest fungicide program terminating in mid-August will probably prove adequate, whereas a September spray may be more critical if the first summer spray was delayed or in years where frequent downpours eliminated fungicide protection between sprays.
   
2. Is the orchard in question a known problem block that is consistently exposed to high inoculum and/or slow drying conditions?  If so, apply a September fungicide spray to at least the orchard perimeter rows where inoculum levels are highest.
   
3. Are extended wetting periods predicted for the first 15-20 days of September?  Orchards with high inoculum or sketchy spray coverage during summer should be recovered in September prior to predicted wettings that might last 3-5 days (e.g., a hurricane coming up the east coast).
   
4. Does the orchard contain clustered fruit where coverage from August sprays may have been less than perfect?  If so, an extra spray in September may help to cover fruit that shifted position since the last spray in mid-August.

   Even if fungicides are applied at the correct times, control failures can occur due to poor spray coverage.  Using more water per acre and reducing travel speeds can provide improved coverage, especially for heavily cropped trees where fruit are clustered on limbs. 

   There has been little research on the value of spray adjuvants for improving fungicide activity against flyspeck.  However, a good spreader/sticker might improve fungicide coverage and retention for sprays applied in late summer.  Be aware, however, that using too much spreader can actually increase run-off from the fruit, thereby reducing fungicide residues.  A really effective sticker might prevent fungicides from redistributing to the back sides of fruit during subsequent wettings.  Thus, I am reluctant to recommend any specific adjuvants for late summer sprays because I’m not certain how they will affect flyspeck control.

Reference cited

Rosenberger, D.A. and Meyer, F.W. 2006. Post-infection control of flyspeck with new fungicides, 2005. Fungicide and Nematicide Tests (online.) Report 61:PF024. DOI:10.1094/FN61. The American Phytopathological Society, St. Paul, MN. http://www.apsnet.org/online/FNTests/reports/2006/PF024.pdf

This material is based upon work supported by Smith Lever funds from the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

Scaffolds is published weekly from March to September by Cornell University -- NYS Agricultural Experiment Station (Geneva), and Ithaca -- with the assistance of Cornell Cooperative Extension. New York field reports welcomed. Send submissions by 3 p.m. Monday to:

Scaffolds Fruit Journal
Editors: A. Agnello, D. Kain
Dept. of Entomology, NYSAES
P.O. Box 462
Geneva, NY 14456-0462
Phone: 315-787-2341 FAX: 315-787-2326
E-mail: ama4@cornell.edu

Online at <http://www.nysaes.cornell.edu/ent/scaffolds/>