VIEW ARTICLE

Ecology and Epidemiology

Epidemiology of Grape Powdery Mildew: A Model. Mary Ann Sall, Assistant professor, Department of Plant Pathology, University of California, Davis 95616; Phytopathology 70:338-342. Accepted for publication 19 October 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-338.

A mathematical model is formulated to describe the increase of grape powdery mildew from bud break until fruit softening on leaves and fruit of cultivar Carignane. The purpose of the model is to examine the influence of seasonal weather patterns and timing of the initial occurrence of infections on the eventual colonization of grape leaves and fruit by the fungus. The basic structure of the model is derived from Vanderplank’s equation for disease development. However, in the powdery mildew model, plant growth is stimulated to allow changes in susceptible tissue during the growing season and is a function of ambient temperature. The basic infection rate (r) varies as a function of ambient temperature and moisture conditions. The model is validated by the close agreement of model results with epidemics observed on cultivar Carignane grapes in 1976 and on cultivar Emerald Riesling grapes in 1977. The most severe powdery mildew is predicted for years with warm spring weather and the least when spring temperatures are coolest. The level of infection at fruit softening is significantly reduced when initial infections occurred more than 2 wk after bud break.