Overwintering of Uncinula necator in Austrian vineyards

Studies on the overwintering of Uncinula necator in Austrian vineyards were carried out from 1994 to 1998. There was no evidence of mycelium overwinte ring in infected buds and only a negligible number of cleistothecia were fo und overwintering on bark. They were, however, discovered on canes in all t he vineyards examined. The density of cleistothecia on these canes was clos ely related to the fungicide treatment applied during the preceeding season and there were marked annual differences in density, which peaked in 1994 and 1995. The middle part of the canes was more frequently contaminated wit h cleistothecia than the basal or upper parts. U. necator cleistothecia are more frequent in Austrian vineyards than hitherto supposed and might be a source of primary inoculum for grapevine powdery mildew infections.