Nectria Canker (European Canker)

Apple or pear develops elliptical, sunken cankers on year-old twigs around leaf scars, with concentric callus rings forming yearly. Neonectria ditissima enters via fall rain and leaf scars in coastal high-rainfall areas. Cut out cankers during dry weather and disinfect tools. Choose less susceptible cultivars like Golden Delicious.

Prune out cankered branches at least six inches below visible symptoms, making cuts into healthy wood. Sterilize your tools between cuts. Canker pathogens typically enter through wounds, so minimize pruning injuries and avoid working on trees when bark is wet. Maintain tree vigor through proper watering and avoid stress from drought or compacted soil, which makes trees more susceptible.