Shot Hole Disease
Wilsonomyces carpophilus (Stigmina carpophila)
Overview
A fungal disease of stone fruits and ornamental Prunus species where leaf spots dry out and fall away, leaving circular holes that give the appearance of shotgun damage. Shot Hole Disease 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: Wilsonomyces carpophilus (Stigmina carpophila). In regenerative gardens, prioritize sanitation, airflow, and unbroken soil cover over calendar spraying, and intervene early when symptoms appear.
Symptoms
Small, reddish-brown spots on leaves that enlarge and develop tan centers. Dead tissue falls out leaving circular holes (shot holes). Spots on fruit become raised and corky. Twig cankers. Bud death. 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
Apply dormant copper spray before bud break. Prune to improve air circulation. Remove infected twigs. Avoid overhead irrigation. Plant resistant varieties. 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
Dormant copper spray in fall and/or late winter. Remove infected twigs and branches. Improve air circulation. Fungicide applications during wet spring weather. 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.