Symptoms
Angular yellow patches on upper leaf surface. Grayish-purple fuzzy growth on leaf undersides. Progressive leaf death from older to younger leaves.
Prevention
Provide good air circulation (proper spacing). Avoid overhead irrigation. Water early morning. Use resistant cultivars. Remove infected plant debris.
Treatment
Organic
Copper-based fungicide (Bordeaux mixture). Potassium bicarbonate spray. Bacillus subtilis biological control.
Chemical (last resort)
Apply metalaxyl or mancozeb. Alternate fungicide groups. Treat preventively in wet weather before symptoms appear.
Affects 6 crops
Sources
MARDI Plant Pathology Guide