Powdery Mildew

Marijuana Horticulture

by Jorge Cervantes

Identify

First indication f infection is small spots on the tops of leaves. At this point the disease has been inside the plant a week or more. Spots progress to a fine, pale, gray-white powdery coating n growing shoots, leaves, and stems. Powdery mildew is not away limited to the upper surface of foliage. Growth slows, leaves yellow, and plants die as the disease advances. Occasionally fatal indoors, this disease is at its worst when roots dry out and foliage is moist. Plants are infected for weeks before they show the first symptoms.

Control

Prevent this mildew by avoiding cool, damp, humid, dim grow room conditions, as well as fluctuating temperatures and humidity. Low light levels and stale air affect this disease. Increase air circulation and ventilation, and make sure light intensity is high. Space containers far enough apart so air freely flows between plants. Allow foliage t dry before turning off the lights. Remove and destroy foliage more than 50 percent infected. Avid excess nitrogen. Copper and sulfur-lime sprays are a god prophylactic.

Biological Control

Apply Serenade or spray with a saturation mix of baking soda and water.

Sprays

Bordeaux mixture may keep this mold in check. A saturation of baking soda spray dries to a fine powder on the leaf; the baking soda changes the surface pH of the leaf to 7, and powdery mildew cannot grow.