How to Manage Pests

Pests in Gardens and Landscapes

Downy mildew—Pseudoperonospora cubensis

Downy mildew attacks all cucurbits, although cucumber is the most commonly infected. It appears first as small, pale green to yellow, angular spots delimited by leaf veins that give the foliage a mottled appearance. Eventually the spots coalesce and the leaf will turn brown. During moist weather, the lower surface of the leaf may be covered with a white to purple growth. Older leaves become infected first.

Identification

Solutions

Spores of the downy mildew fungus are carried by air currents or by rain-splash or sprinklers. A wet leaf surface is required for infection. Avoid using overhead sprinklers. Spacing plants to reduce canopy density and humidity will reduce spread. Some varieties of cucumber, melons, and watermelons may show resistance.

Downy mildew on cantaloupe leaf
Downy mildew on cantaloupe leaf


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