Leaf Spot
Septoria spp., Cercospora spp., Alternaria spp., Phyllosticta spp., Bipolaris spp.
Overview
A general term for various fungal and bacterial diseases that cause discrete spots or lesions on leaves. Spots may be circular, angular, or irregular, and often have distinct borders or halos. 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: Septoria spp., Cercospora spp., Alternaria spp., Phyllosticta spp., Bipolaris spp.. In regenerative gardens, prioritize sanitation, airflow, and unbroken soil cover over calendar spraying, and intervene early when symptoms appear.
Symptoms
Circular to irregular spots on leaves, often with tan, brown, or dark centers and distinct margins. Spots may coalesce, causing large areas of dead tissue. Premature defoliation in severe cases. 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
Ensure adequate spacing for air circulation. Avoid overhead watering. Remove fallen leaves and debris. Rotate crops. Use disease-free seed and transplants. 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-based or broad-spectrum fungicides. Remove severely infected leaves. Improve air circulation through pruning. Mulch to prevent soil splash onto lower leaves. 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.