INFLUENCE OF SUN EXPOSURE ON POWDERY MILDEW DEVELOPMENT

Powdery mildew is often most severe in portions of the vineyard and/or individual canopies that are subject to shading. Although this phenomenon is widely recognized, it has received relatively little formal study. Willocquet et al. (1996) showed that UV-B radiation negatively impacted both conidial germination and mycelial growth of Uncinula necator. They suggested that solar radiation is an important factor in the development of grape powdery mildew epidemics, and that training systems that increase exposure of the vines to sunlight could help to reduce disease development. Our field experience suggests that powdery mildew may be a particular problem not only in specific vineyard and canopy locations subjected to shading, but also regionally in seasons with reduced solar radiation resulting from prolonged periods of cloudy weather.