Meteorological Factors Affecting Airborne Conidia Concentrations and the Latent Period of Podosphaera clandestina on Sweet Cherry.

Conidia of Podosphaera clandestina were trapped beginning about 1 month after bud burst and continuing through the majority of the fruit development period and beyond. The presence of airborne conidia generally followed a diurnal pattern, with peak concentrations occurring in late morning to early afternoon. The three general spore dispersal patterns described by Sutton and Jones for P. leucotricha were observed: diurnal dispersal with concentrations peaking about midday (type I dispersal); random dispersal in which the spore concentrations were not correlated with any measured meteorological parameter (type II dispersal); and dispersal associated with the onset of rain (type III dispersal). Positive correlations with wind speed and temperature, and negative correlations with relative humidity, were characteristic of days when spore dispersal was diurnal. Consistent correlations with meteorological parameters were not detected on days with random or rain-onset dispersal. The latent period of P. clandestina on cherry foliage was found to be shortest at 20 to 25°C and was influenced by temperature and incubation time.