Branch Canker

You'll notice sunken, dark brown cankers on branches of stressed trees, sometimes with a sharp border between the diseased bark and healthy tissue. Affected branches may show leaf scorch, wilting, or early leaf drop, especially if the canker girdles the branch completely. Smaller cankers appear as slight depressions, while older ones can be scarred and cracked or ringed with target-like patterns. Multiple fungi cause this problem, so diagnosis usually depends on what tree species is affected and what conditions preceded the canker.

Branch canker is an opportunistic disease that exploits stress, so preventing it means reducing wounding and keeping your trees vigorous. Trees under drought stress, frost damage, or construction impact are most vulnerable to infection through wounds or natural openings. Space plants for airflow, avoid unnecessary pruning wounds, and provide consistent deep watering during dry periods. Once a canker forms, prune the entire branch about one foot below the affected area and remove it from the site. White latex paint on southwest-facing trunks prevents sun-scald cracks that invite infection.