Cercospora Leaf Spot
Cercospora spp.
Overview
A widespread fungal disease affecting many crops, causing circular to angular spots with gray to tan centers and reddish-brown to purple borders on leaves. Cercospora Leaf Spot spreads mainly by spores on wind, splash, tools, and crop debris. Humid, crowded plantings and overhead watering favor outbreaks in home gardens and food forests. Causal agent: Cercospora spp.. In regenerative gardens, prioritize sanitation, airflow, and unbroken soil cover over calendar spraying, and intervene early when symptoms appear.
Symptoms
Circular to angular leaf spots with gray to tan centers and dark reddish-brown or purple borders. Spots may coalesce into large necrotic areas. Premature defoliation reduces yield and quality. Compare several plants and note whether symptoms spread after rain, insect feeding, or wet foliage. Photograph undersides of leaves and cut stems when wilt is present to refine the diagnosis. Rule out simple drought, fertilizer burn, and herbicide drift before assuming a pathogen - abiotic injury often mimics disease.
Environmental Conditions
Humid
Prevention
Rotate crops. Use resistant varieties. Ensure adequate spacing. Avoid overhead irrigation. Remove crop debris after harvest. Mulch to reduce splash, clear season-end debris, and avoid working plants when wet. Design beds for airflow and diverse plantings that support beneficial insects without creating permanent humid pockets around susceptible crops.
Management
Apply copper or chlorothalonil fungicides. Remove severely infected leaves. Improve air circulation. Avoid working with wet plants. Prefer drip irrigation, morning watering, and open spacing so leaves dry quickly. Disinfect pruners between cuts on woody plants. Use copper, sulfur, or biological products only as labeled protectants when pressure is high - they rarely reverse advanced infections alone. Destroy (do not casually compost) highly infectious debris.