Can We Predict Flyspeck Development? 



James C. Hall, Michael Frank, Arthur F. Tuttle, and Daniel R. Cooley 

 Department of Microbiology, University of Massachusetts 



Flyspeck, caused by Schizothyrium pomi 

 and sooty blotch, caused by a group of fungi 

 including Peltaster fructicola, Leptodontium 

 elatius, and Geastrumia polystigmatis are two 

 common summer diseases of apple in New 

 England. Recently, summer diseases have 

 become more problematic due at least in part to 

 the decreased use of fungicides such as 

 mancozeb and captan, attributable to 

 increased label restrictions, cost cutting, and 

 the implementation of IPM programs 

 (Rosenberger, Proc. New England Fruit 

 Meetings \02:b\-bl, 1997). In July and August, 

 growers are limited to a few fungicide 

 applications, generally using captan with or 

 without a benzimidazol. Growers could more 

 effectively control sooty blotch and flyspeck 

 within the confines of an IPM program if they 

 were able to time their sprays better so as to 

 correspond to infection and the eventual 

 appearance of these diseases. Specifically, a 

 more economical and effective application of 

 fungicides could be accomplished if growers 

 were able to predict the appearance of flyspeck 

 disease and sooty blotch. It would then be 



possible to replace a preventative spray 

 program with one or more eradicant sprays 

 timed to thwart the appearance of these 

 diseases. 



In North Carolina, Brown and Sutton 

 {Plant Disease 79:1165-1168) have developed a 

 model for the prediction of sooty blotch and 

 flyspeck disease symptoms on apples. The 

 model is based on leaf wetness data collected at 

 three different sites in North Carolina from 

 1987 through 1994, coupled with known 

 biological information about the fungi involved. 

 From these data, the researchers concluded 

 that the best estimate of flyspeck and sooty 

 blotch symptom occurrence was based on the 

 cumulative hours of leaf wetness during 

 periods of at least four hours duration, 

 beginning from the first rainfall at least 10 

 days after petal fall. Brown and Sutton chose to 

 include periods of at least four hours because 

 they had previously demonstrated that the 

 pathogens required about four to five hours of 

 constant wetting in order to germinate (Plant 

 Disease 77:451-455). Under these conditions, 

 the researchers found that flyspeck and sooty 



Fruit Notes, Volume 62 (Number 4), Fall, 1997 



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