Powdery Mildew
Erysiphe spp., Podosphaera spp., Sphaerotheca spp., Golovinomyces spp., Leveillula spp.
Overview
A widespread fungal disease that forms a white to grayish powdery coating on leaf surfaces, stems, and sometimes flowers and fruit. Caused by various species of obligate parasitic fungi in the order Erysiphales. Powdery Mildew 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: Erysiphe spp., Podosphaera spp., Sphaerotheca spp., Golovinomyces spp., Leveillula spp.. In regenerative gardens, prioritize sanitation, airflow, and unbroken soil cover over calendar spraying, and intervene early when symptoms appear.
Symptoms
White to gray powdery patches on upper leaf surfaces, stems, buds, and flowers. Leaves may yellow, curl, and drop prematurely. Severe infections cause stunted growth and reduced yields. 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
Plant resistant varieties. Ensure adequate air circulation and spacing. Avoid overhead irrigation. Prune to improve airflow. Apply preventive sulfur or potassium bicarbonate sprays. 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 neem oil, sulfur-based fungicides, or potassium bicarbonate at first signs. Remove and destroy infected plant material. Milk sprays (1:9 ratio) can be effective. Biological controls include Bacillus subtilis products. 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.