Canker

Cankers are sunken, elongated lesions on branches and trunks, often appearing as wounds that fail to heal normally. You'll notice the tissue around the canker may have a rough, cracked appearance, and the wood beneath often shows discoloration ranging from cinnamon-brown to dark black. On some hosts like poplars and willows, cankers can girdle branches and cause the section beyond to die back. In Western Washington's cool, moist climate, these lesions can persist for years, creating entry points for secondary pathogens and gradually weakening your trees.

Canker diseases are caused by fungi that exploit wounds and stressed areas on trees. Cold injury, storm damage, pruning wounds, and environmental stress all create openings for infection. The fungus colonizes the cambium and conducts vascular tissues, cutting off nutrient and water flow. Management focuses on prevention and clean pruning practices: avoid wounding trees during the growing season; space seedlings and young trees well apart for good air circulation; don't over-fertilize or irrigate late in the season, which creates succulent growth more prone to damage; and when you must prune, do so during dormancy and sterilize tools between cuts to avoid spreading spores between plants.