How to Manage Pests

Pests in Gardens and Landscapes

Pest identification and confirmation—Downy mildew

Downy mildew gets its name from the downy masses of spores it produces on undersides of affected leaves. These downy growths initially may be confused with those of powdery mildew. However, the two diseases differ in several important ways. The white sporulation of powdery mildew covers much of both the lower and upper sides of the leaf. Downy mildews are favored by cool, moist conditions while powdery mildew are favored by warm, dry conditions. 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 there is in downy mildew infections.

Spores of downy mildew
Spores of downy mildew

Spores of powdery mildew
Spores of powdery mildew


Statewide IPM Program, Agriculture and Natural Resources, University of California
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