Stemphylium blight: Lesions formation on leaves
Pathogen: Stemphylium vesicarium
Symptoms
Lesions are often more numerous on the sides of onion leaves facing the prevailing wind.The centers of lesions turn brown to tan, then dark olive brown and finally black as the fungus sporulates.
Disease development
Extended periods of leaf wetness from dew formation, rainfall or overhead irrigation during bulb formation and development can result in severe leaf blighting. Bulb size can be greatly reduced due to loss of foliage. Infection is usually limited to leaves and does not extend down to the scales of the bulb.
Disease management
Chemical control with fungicides is effective in reducing disease development. Long term rotation with unrelated crops may reduce losses. Also, good field drainage and reduced plant density may lessen disease severity.
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