Meteorological conditions determine the thermaltemporal position of the annual Botrytis bunch rot epidemic on Vitis vinifera L. Cv. Riesling grapes

Abstract

Under Central European climatic conditions, bunch rot caused by Botrytis cinerea occurs virtually every season on Vitis vinifera L. cv. Riesling grapes. Statistical investigations based on at least three annual disease severity assessments in 7 seasons (20072013) aimed at (i) simulating the disease progress and (ii) identifying meteorological conditions with predictive value for epidemics. Methods and results: Sigmoidal regression models were used to describe the disease progress as function of thermal time. Coefficients of determination were > 0.97. The thermal time adjusted pace of the epidemic was almost constant in all seasons while the point of time when 5% disease severity was reached varied among years. Window pane analyses showed that relatively low temperatures and wet conditions during bloom as well as relatively high temperatures and low precipitation sums around/after veraison were associated with thermaltemporally late epidemics. Conclusions: Environmental conditions determine the timing of annual bunch rot epidemics. Analyses indicate a strong link between meteorological conditions around grape bloom (probably affecting fruit set and cluster structure) and the predisposition of the grape clusters to bunch rot.