How to Manage Pests

Pests in Gardens and Landscapes

Seasonal development and life cycle—Purple blotch

Stemphylium leaf blight and purple blotch are both favored by foggy and rainy weather; optimum temperature for disease development is about 73° to 77° F. The spores are airborne. In California, these diseases are often associated with downy mildew lesions on onions; they occur less commonly on garlic.

Stemphylium leaf blight lesion
Stemphylium leaf blight lesion

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