Flyspeck

        Flyspeck has been a problem in numerous Maine orchards in recent years.  The wet weather in fall 2005 provided conditions for increased flyspeck inoculum on border row host plants going into spring 2006.  The wet weather in May, and especially in June 2006 gave flyspeck a good start for establishing new conidia-producing colonies.  July and August have not been nearly as wet as June, but still had higher than normal amount of rain.  Thus, the flyspeck inoculum level at this time could be above normal.

 

        Flyspeck should not become a problem where the final fungicide application is made late enough so that less than 270 leaf wetness hours accumulate between fungicide depletion and harvest.  The flyspeck fungicide spray timing estimates at http://pronewengland.org/AllModels/MEmodel/RADARME-MonmouthLate.htm#FLYSPECK can help account for recent and forecast weather in identifying the earliest safe final spray date.

 

        As of today, the estimates are that a full-dose application of strobilurin (Flint, Sovran, Pristine), captan, or half-dose captan + Topsin M made prior to August 21 will lose efficacy by August 27 or earlier.  Starting from August 27, average wetness hours accumulation would reach the required 270 hours for flyspeck colonies to become visible by October 2.  Of course, earlier final fungicide spray dates with an earlier depletion date naturally have an earlier date when flyspeck could begin appearing.

 

        McIntosh harvest timing so far looks like it will be about normal this year, reaching into the last week of September.  If you had solid flyspeck protection through June-August, and if your final fungicide application was after August 12, AND if September wetness hour accumulation is normal, then McIntosh harvest should be winding down before the first flyspeck infections that start after fungicide coverage wears off will have had enough time to begin appearing.  That scenario leaves later harvested cultivars at risk of having flyspeck appear before harvest.  It also assumes that apples going into storage do not stay warm enough or wet enough for flyspeck development after harvest.  And it assumes that there were substantial gaps in fungicide coverage in July and August, and/or if September is wetter than normal, then flyspeck colonies could begin appearing even before the end of McIntosh harvest.

 

        The long term forecast is for increased chance of higher than normal temperatures in September.  Warm temperatures in September favor increased flyspeck development.  The optimum temperature for flyspeck growth is in a range from about 61 – 75F, with peak growth around 68F.  Average mean daily temperature in September is around 58F.  So above normal September temperatures would provide more favorable growing conditions for flyspeck.  

 

Of course, it is moisture that really drives flyspeck risk.  The outlook for the remainder of August is for above normal chance of rain.  The long-term rain forecast for September is neutral.

 

Another major factor driving flyspeck risk is site characteristics.  Thick canopy trees in a location with poor air drainage and high humidity have much greater risk than small open trees on a windy site.

 

        “Low risk” sites without a history of flyspeck problems might not need fungicide renewal after the August 20 rain to prevent flyspeck problems for September harvest apples.  For “medium risk” sites with some history of flyspeck, or for October-harvested applies, the outlook  leans more towards needing to renew coverage to reduce risk of flyspeck problems.  For “high risk” sites with a history of flyspeck problems, there is good reason to renew fungicide protection after coverage applied prior to August 21 wears off.    

 

        If you gamble on a “not-wet” September and do not renew fungicide coverage, it would be wise to keep watching the weather for the next couple of weeks and be ready to respond if wet conditions prevail and you change your mind about the degree of flyspeck risk.

 

         Dr. David Rosenberger at Cornell University has published an article reviewing current thinking on flyspeck management.  The full article will soon be available at  http://www.nysaes.cornell.edu/ent/scaffolds/2006/060821.html .   The concluding section from that article is shown below:

 

“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 and/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 and 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.”

 

 

Insects

 

        Where the final insecticide application was made prior to the August 20-21 rain, there is potential for apple maggot to become a problem.  Apple maggot are more of a problem on earlier maturing cultivars, and conversely on the latest maturing cultivars that are the only fruit egglaying sites left as other cultivars are harvested.  Apple maggot numbers vary so much between orchards that it is not possible to speculate on a general recommendation at this point.

 

        Where late season codling moth or lesser appleworm have been a problem in past years, now is good timing for a final application to control second generation larvae before they infest calyx ends of apples.

 

        Second generation white apple leafhopper nymphs should be appearing now.  A number of Maine orchards had substantial numbers of first generation white apple leafhopper back in June.  If you see more than 3 nymphs per leaf, then there is a chance of crop injury through foliar feeding or from WAL honeydew staining the fruit.  Preventing ‘picker nuisance’ may require a lower threshold.  

 

You may be able to control WAL by spot treating if the infestation is limited to a certain section of the orchard.  Sevin, Assail, Calypso, Avaunt, Pyganic or a pyrethroid used for apple maggot and codling moth will also provide excellent white apple leafhopper control.  SpinTor is not effective against WAL.  Imidan is poor against WAL, but still might give enough control to meet your objectives. 

 

Timing is a key to successful WAL control.  None of the insecticides are as effective against adults as they are against the nymphs, so this is the time to make a decision about whether 2^nd generation WAL require treatment.    

 

- Glen

 

 

Glen Koehler
Pest Management Office
491 College Avenue
Orono, ME  04473
Voice:  207-581-3882
Email:  gkoehler@umext.maine.edu
Web:  PRONewEngland.org
Fax:  207-581-3881

TDD 1-800-287-8957

 

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