Downy mildew is a major disease for grapes in regions with warm, wet climates like the Midwest. It causes deformities and premature defoliation of grapevines, impacting fruit ripening and winter hardiness. The fungus overwinters in leaf debris and spreads via rain-dispersed spores, causing yellow-green lesions on leaves and gray, fuzzy berries. Proper site selection, resistant cultivars, good pruning and fungicide application are all important for disease control.