How to Manage Pests

Powdery mildew on lettuce—Erysiphe cichoracearum

Powdery mildew usually appears first as yellow spots on the upper leaf surface of older leaves; these spots develop the characteristic powdery growth and symptoms spread to the undersides of leaves and stems. Affected leaves may turn completely yellow and die.

Identification

Powdery mildew is often confused with downy mildew. Both downy mildew and powdery mildew produce whitish collections of spores on the leaf surface, but similarities end there. In powdery mildew the white sporulation covers much of both the lower and upper sides of the leaf; downy mildew spores appear mostly on the undersides of leaves. Downy mildew spores are produced on branched stalks that look like little trees, whereas powdery mildew spores occur in chains on a single stalk. Areas affected with powdery mildew enlarge in a circular pattern, spreading a white, dusty growth over the whole leaf; there is no clear veinal delineation as in downy mildew infections. Powdery mildew thrives in warm weather; downy mildew is a cool-weather disease.

Solutions

Powdery mildew rarely becomes serious enough to require treatment.

For more information, see the Powdery Mildew Pest Note.