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.
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Stemphylium
leaf blight lesion
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