Onion leaves infected by this fungal disease develop white lesions surrounded by water-soaked halos. As the disease progresses, straw-colored slits may appear, and the leaves can collapse and present a “blasted” appearance. Onion leaf blight also attacks garlic and other plants in the onion family. Older leaves are more susceptible to the disease than younger leaves.
Cool, wet weather or periods of high humidity favor development of the disease. Spores overwinter on onion bulbs and leaves left in the soil. Onion leaf blight is relatively common east of the Rockies.
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