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 the 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. Downy mildew produces spores mostly on the undersides of leaves and only after rain or very heavy fog. Spores disappear soon after leaves dry out. Powdery mildew does not require water on the leaf surface for spore formation, and the powdery growth appears on both sides of leaves. Powdery mildew thrives in warm weather whereas downy mildew is a cool weather disease. Dry, desiccating winds and clear, warm days inhibit growth and spread of downy mildew.

Fuzzy spores on underside of leaf
Fuzzy spores on underside of leaf

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