Overwinters on diseased plant refuse in the soil. Lives on the leaf surface. Sends out hollow tubes into the plant to suck out nutrients. It is a fungal disease with a white to grayish powdery growth, usually on the upper surfaces of leaves. Small black dots appear and produce spores that are blown by wind to infect new plants.
Growth is enhanced by low light levels that accompany cloudy or foggy periods.
Cannot survive if there is a film of water on leaves or stems. The best time to examine plants is early in the morning while dew is on the leaves. The first symptom is sunken, water-soaked spots on leaves, either yellowish or grayish in color. Spots later become covered with a downy purplish mold growth which may eventually be blackened by a second fungus. Infected leaves become covered with a grayish-white powdery fungus growth.