Controlling Powdery Mildew on Pumpkins and Squash

White, powdery coating on pumpkin leaves is powdery mildew, a common fungal disease. It spreads rapidly in warm, humid conditions. Fungicides like chlorothalonil (Daconil) can control it, but treatment must start early—when plants are 12 inches tall—and continue on a schedule. By late July, heavy infection may be too advanced to save the crop.

Prevent future outbreaks by spacing plants for airflow, watering at the base (not overhead), and choosing resistant varieties. Remove and destroy infected leaves at season's end to reduce overwintering spores.