Powdery Mildew

Powdery mildew is an important disease of grapes in Minnesota that reduces vine growth and yield if left untreated. It is caused by the fungus Uncinula necator, which overwinters in bark crevices and releases spores in the spring that infect green grape tissues. Symptoms include a white or gray powdery growth on leaves, shoots, and berries. Infection can cause berries to split open or remain uncolored. Proper site selection, resistant varieties, pruning, and a fungicide spray program starting early in the season are key control strategies.