How to Manage Pests

Pests in Gardens and Landscapes

Powdery mildew—Sphaerotheca fuliginea and
Erysiphe cichoracearum

Two species of fungi can cause powdery mildew on cucurbits: Sphaerotheca fuliginea and Erysiphe cichoracearum. S. fuliginea is the more common. E. cichoracearum can, however, be common in areas with cool springs and summers. All cucurbits are susceptible to powdery mildew, but the disease is less common on watermelon than on other cucurbits. Powdery mildew first appears as pale yellow spots on stems, petioles, and leaves. These spots enlarge as the white, fluffy mycelium grows over plant surfaces and produces spores, which give the lesions a powdery appearance. Affected leaves become dull, chlorotic, and may wilt in the afternoon heat; eventually they become brown and papery. Plants may die.

Life cycle


Control weeds and follow good sanitation practices. Avoid overhead sprinklers. A few resistant varieties are available. Applications of sulfur may be needed. Good coverage of undersides of leaves are required. Note that some cucurbit varieties are sensitive to sulfur.

For more information, see the Powdery Mildew Pest Note.

Powdery mildew on cucurbit leaves
Powdery mildew on cucurbit leaves

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