Downy Mildew

Marijuana Horticulture

by Jorge Cervantes

Identify

Sometimes called false mildew, downy mildew affects vegetative and flowering plants. Young, succulent foliage is a favorite starting place. Powdery mildew develops in temperatures below 76F. It appears as whitish-yellow spots on top of leaves creating pale patches. Grayish mycelium spawn is on leaf undersides, opposite the pale patches.

Downey mildew can spread very quickly, causing a lack of vigor and slow growth; leaves yellow, die back, and drop. The disease is in the plant system and grows outward. It is often fatal, spreads quickly, and can wipe out a crop. Avoid promoting this disease by not crowding plants. Keep temperatures above 76F and the humidity below 50 percent.

Control

Cleanliness! Use sterile growing medium. Remove and destroy affected plants, not just foliage.

Biological

Apply Serenade (Bacillus subtilis). Bordeaux mixture is also somewhat effective.