Effect of Temperature and Relative Humidity on Development of Cercosporidium personatum on Peanut in Georgia

In controlled environment experiments, a minimum of 4 hr of relative humidity ?95% per day was required for conidial production by Cercosporidium personatum, and the highest numbers of conidia were produced when lesions were subjected to daily periods of 16 or more hours of relative humidity ≥ 95%. The optimum temperature for spore production was near 20°C. In field studies, numbers of airborne conidia of C. personatum, the causal agent of peanut late leaf spot, were monitored with Burkard 7-day recording volumetric spore traps at Athens, Plains, and Tifton, Georgia, in 1986-1988. Trapping of conidia was initiated in mid-July to early August, when late leaf spot lesions were first detected. A diurnal periodicity in spore release was observed, with peak spore catches occurring between 10 a.m. and 6 p.m. Conidia were detected on most days during the trapping period. For the years and locations examined, duration of relative humidity ≥ 95% generally exceeded 5-hr duration each day and temperatures seldom dropped below 20°C, indicating that conditions in Georgia were generally favorable for spore production.