Thousand Cankers Disease

This Pest Alert developed by the USDA Forest Service Northeastern Area State and Private Forestry provides basic information about disease symptoms, the fungus associated with the disease, and the walnut twig beetle that carries the fungus.

Publication highlights:

• Geosmithia morbida is the fungus that causes these cankers
• the walnut twig beetle (Pityophthorus juglandis) carries the fungal spores that infects plant tissue
• the beetle has not caused significant branch mortality by itself
• the fungus and beetle only occur on walnut species
• the first confirmation of the beetle and fungus within black walnut's native range was in Knoxville, TN in 2010
• symptoms include:
• yellowing foliage leading to branch mortality
• circular to oblong cankers under the bark that kill the cambium
• numerous tiny entrance and exit holes on dead or dying branches

The potential damage of this disease to eastern forests could be great because of the widespread distribution of eastern black walnut, the susceptibility of this tree species to the disease, and the capacity of the fungus and beetle to invade new areas and survive under a wide range of climatic conditions in the west.

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