Canker
Nectria spp., Cytospora spp., Botryosphaeria spp., Diaporthe spp., Phomopsis spp.
Overview
A general term for localized dead areas on bark of woody plants caused by various fungi and bacteria. Cankers may girdle branches or trunks, causing dieback above the infection point. Canker 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: Nectria spp., Cytospora spp., Botryosphaeria spp., Diaporthe spp., Phomopsis spp.. In regenerative gardens, prioritize sanitation, airflow, and unbroken soil cover over calendar spraying, and intervene early when symptoms appear.
Symptoms
Sunken, discolored, dead areas on bark. Cracked or peeling bark around lesion margins. Gumming or resin exudation. Branch dieback above cankers. Fruiting bodies may be visible on canker surfaces. 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
Variable
Prevention
Maintain tree vigor through proper watering and nutrition. Avoid wounding bark. Prune during dry weather. Paint large pruning wounds. Plant adapted species for the site. 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
Prune out cankered branches well below the canker margin. Sterilize pruning tools. Improve tree vigor. Copper sprays may prevent new infections. Remove severely infected trees. 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.