Weather conditions are a determining factor in the severity of this disease and it will, if left untreated, persist year after year. Powdery mildew will initially appear as light green to yellow spots. Typically spidery or threadlike white patches develop peppered with minute black fruiting bodies. The plant gives the appearance of having been dusted with flour or talcum powder. Powdery mildew is most likely to attack in the spring and the fall when the weather is cool and the humidity is high.
Most powdery mildew develops as thin layers of mycelium on the plant's surface.
Spores or resting bodies make up the bulk and are the primary means of dispersal. Powdery mildew spores are carried by the wind and rain to new hosts. Excess water on the plant's surface can kill spores and inhibit growth of mycelia, and both spores and mycelia are sensitive to extreme heat and direct sunlight. Control To lessen the chance of the disease occurring, plant in non-shaded areas. Space plants providing enough aeration and growing room.