Botrytis leaf blight: Silivery-white spots on onion leaves
Pathogen: Botrytis squamosa
Symptoms
Spots often surrounded by slivery-white ‘halo’. Active lesions are grayish-white colour. Small (1 to 5 mm) grayish-white oval shaped lesions. Older lesions tend to be brownish-white and desiccated (dehydrated or dried out). When numerous lesions are present the leaf tips begin to dieback, eventually affecting the entire leaf.
Disease Development
The fungus may over-winter in infected plant material or may survive in the soil as small, dark brown sclerotia. During moist periods with moderate temperatures, fungal spores are dispersed from sclerotia, infected leaves and debris to initiate infection. This disease can spread rapidly when environmental conditions are favorable for development.
Disease Management
Plant onions in single rows allowing at least 30 cm between plants to promote good air circulation and quick drying of foliage after rain; time irrigation to allow plants time to dry out sufficiently; apply appropriate fungicide sprays when plants have at least five true leaves and early symptoms of disease.
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