Onion Leaf Blight

Botrytis Squamosa

This fungal disease manifests itself as whitish spots or lesions on older leaves (younger ones are less affected). Eventually these become sunken and straw colored and may have lengthwise splits in them. The tip of the leaf commonly dies back also and the reduced leaf area results in smaller bulbs.

Onion Leaf Blight is most often a problem in cool (50 F to 75 F), wet weather when the leaves remain wet for extended periods.

Control Onion Leaf Blight by removing all onion crop debris (don’t leave any tops on soil) and any volunteer onions left behind or resulting from seed. You should also rotate your crops and make sure there is good air circulation. Some varieties have some resistance to it.

Image: Lindsey du Toit, Washington State University, Bugwood.org