Tree cankers: ID and tree-level disease risk

A canker is a sunken, dead area in bark or cambium caused by a fungal or bacterial pathogen. Cankers vary enormously in severity -- from cosmetic blemishes on otherwise healthy trees to girdling infections that kill large branches or entire trunks within a season. The key variable is not the.

A canker is a sunken, dead area in bark or cambium caused by a fungal or bacterial pathogen. Cankers vary enormously in severity — from cosmetic blemishes on otherwise healthy trees to girdling infections that kill large branches or entire trunks within a season. The key variable is not the disease itself but the tree's ability to compartmentalize the infection and wall it off from healthy tissue.

What a canker looks like

Per Penn State Extension, cankers share these features:

• Sunken or flattened area of bark: The cankered bark is depressed relative to surrounding healthy bark
• Discolored bark: Brown, dark, or orange-brown rather than the normal gray or brown of healthy bark
• Distinct margins: A clear boundary between living and dead tissue (though this boundary may be obscured in severe infections or weak-willed compartmentalizers)
• Cracked or loosening bark: Over time, dead bark cracks and peels; underneath, the wood may be stained brown or black

Per NC State Extension, the most reliable canker confirmation: cut away a small portion of bark at the boundary and look at the cambium. Living cambium is green; dead cambium is brown. If brown extends into the wood, the cambium is dead at that point.