DIDYMELLA ASCOSPORES IN DERBY

The main Didymella ascospore season in Derby is June-September. 10 day running means for the years 1986-1988 have been compared with 10 day running means of rainfall and maximum temperatures. The high temperatu res reached in 1987 together with substantial rainfall were very favou rable for Didymella ascospore release. Diurnal periodicity showed that the expected night time pattern was only occasionally disturbed by da y time rainfall. Didymella ascospore liberation is greatly increased w hen both temperature and rainfall are high. Temperatures of about 20-d egrees in the period before rainfall appear to greatly increase the nu mbers of Didymella ascospores liberated. Air has been sampled for fung al spores in Derby for many years and there is evidence of an upward t rend in the June-September seasonal mean concentrations of Didymella a scospores since 1985 with no corresponding trend apparent in the corre sponding June-September rainfall totals. Seasonal mean concentrations for 1985, 1987, 1988 and 1992 were at least 82% higher than in earlier years. Short term fluctuations were correlated with June-July precipi tation. Between 1970 and 1991 the acreages of barley and wheat in Derb yshire changed little to 1981 but then more than doubled by 1991. The clinical implications of increasing Didymella ascospore concentrations in Derby and of agricultural changes in Derbyshire are discussed.