Identifying and Treating Alternaria Blight on Cabbage

Symptoms

Circular leaf spots with raised, dark borders—resembling psoriasis—are classic Alternaria blight (Alternaria brassicicola). Starts on lower leaves; spots merge, leaves yellow and die. Plants may succumb if untreated.

Organic Control

1. Remove and destroy affected leaves immediately.
2. Spray copper sulfide (Bordeaux mixture) at first sign; follow label for pre-harvest interval.
3. Improve air circulation: space plants 18–24 inches, avoid overhead watering.
4. Rotate brassicas 3–4 years.

Edibility

Cut out infected areas; unaffected portions are safe to eat after thorough washing. Observe copper product waiting period before harvest.