EFFICACY OF SPRAYS APPLIED AGAINST POWDERY MILDEW (ERYSIPHE NECATOR) DURING A CRITICAL PERIOD FOR INFECTIONS OF CLUSTERS OF GRAPEVINES (VITIS VINIFERA)

Erisyphe necator is one of the most destructive pathogens of grapevines and is normally controlled by seven and more fungicide treatments until veraison of grapes. Two fungicide regimes comprising either 3 or 7 sprays per season were compared in a German vineyard between 1999 and 2010. The trials always included: (i) 3 fungicide sprays, one before flowering, the second during blossoming and the third at berries diameter 2 mm [so called "Open Window Period" (OWP) sprays]; (ii) 7 sprays which included OWP sprays of (i) plus one spray before and three afterwards. The trials were carried out with a single line tunnel-sprayer in 4 replicates, each comprising 12 vines of highly susceptible varieties. Experimental rows were separated by untreated rows on both sides. Although in most years, natural initial inoculum was present, in 2008-2010, the initial inoculum was supplemented with artificial infections on the separating untreated spacer lines. Even under extreme disease pressure, 3 sprays in OWP had nearly the same and always more than 90% of the preventive effect of seven sprays.