Canker is a general term used to describe a number of different diseases that cause unsightly wounds on the stems and branches of trees, usually as the result of fungal or bacterial infection. Cankers are rarely life-threatening, but can cause death of branches if the damaged tissue completely encircles a branch. Equally, deep cankers will weaken the stem or branch and can predispose the tree to damage by the wind. Some fungal cankers can be treated with fungicides.
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This apple canker (Nectria galligena) threatens to encircle this apple sapling, and will likely be terminal.
