Flyspeck and Sooty Blotch: 

 New Problems and New Ideas 



Daniel R. Cooley, Wesley R. Autio, and James W. Gamble 



Departments of Plant Pathology and Plant & Soil Sciences, 

 University of Massachusetts 



For many years, if there was no primary 

 scab, apple growers would reduce drastically, 

 and in a few cases eliminate, summer fungi- 

 cides. Over the past four years, however, the 

 incidences of the summer diseases have in- 

 creased. The most dramatic increases have 



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 a 



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15 



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1982 1984 



1986 1988 

 YEAR 



1990 1992 



Figure 2. Summer-fungicide use in Massa- 

 chusetts IPM orchards. 



been seen in the diseases flyspeck (Zygophiala 

 jamaicensis Mason) and sooty blotch (Gloeodes 

 pomigena (Schw.) Colby), which often occur 

 together and blemish the surface of apples 

 (Figure 1). Initial infections of these diseases 

 start in mid-June, and new infections continue 

 until harvest. Initially, the IPM programs in 

 New England felt that these diseases were in- 

 significant, and in Massachusetts, growers who 

 successfully controlled primary apple scab ( Ven- 

 turia inaequalis) were advised that they did not 

 need to treat any more than 3 times from mid- 

 June to harvest. Over the period 1978 to 1986, 

 sooty blotch and flyspeck damage to fruit aver- 

 aged less than 0.06% in harvest surveys of IPM 

 blocks. Since then, incidence has climbed dra- 

 matically, ranging from 0.1% to 0.7%, on aver- 

 age, and in individual blocks reaching levels in 

 excess of 10%. 



At the same time, fungicide use in the sum- 

 mer has increased. In Figure 2, summer fungi- 

 cide use alone (after June 1 5) is shown. Over the 

 period 1982 to 1987, summer fungicide use was 

 falling in Massachusetts, as measured in IPM 

 cooperator orchards, from an average of 5 dos- 

 age equivalents (DE) to a low of less than 2 DE. 

 In the last 3 years, summer fungicide use has 

 risen, as shown in the graph. 



We think that the increase in sooty blotch 

 and flyspeck in recent years may be attributed 

 to 3 factors: 



• Consecutive years of abnormally warm, 

 wet weather in the Northeast; 



• Changes in fungicide use, specifically: 



a) a reduction in overall summer 

 fungicide use; 



b) reduction and eventual elimina- 

 tion of the most effective chemi- 

 cals (EBDCs) beginning in 1988; 



24 



Fruit Notes, Winter, 1991 



