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Thousand Cankers Disease

Geosmithia morbida
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Thousand cankers disease is a new threat that has been linked to the death of eastern black walnut trees in the United States over the last decade. The native walnut twig beetle (Pityophthorus juglandis) carries spores from an invasive fungus (Geosmithia morbid) that are introduced into the phloem of trees as the beetle constructs galleries through the bark.

The tiny walnut twig beetle creates numerous galleries beneath the bark of black walnut trees which introduces the fungus resulting in disease cankers. Large numbers of cankers form along infected branches and overtake the host tree, resulting in the diseases name – thousand cankers disease.


The full extent of thousand cankers disease is not known as this disease may be confused with other forms of natural mortality. Currently, thousand cankers disease can be found throughout the western United States. Other individual pockets have been reported in New England and in the American plains, as well as Texas and into Florida. The walnut twig beetle which carries the disease is found throughout southwestern United States and Mexico.

Impacts of Thousand Cankers Disease

  • Numerous cankers form across branches restrict the movement of nutrients through the tree.
  • Can kill trees within two to three years once it is infected.
  • The black walnut tree is a highly valued timber species in North America where it is used for high-end cabinetry and other products.
  • Nuts produced by the tree serve an important nutritional role for a wide range of wildlife.

How to Identify Thousand Cankers Disease

  • The disease occurs only on Black Walnut trees.
  • Main symptoms of the disease include dying branches, numerous cankers on branches and evidence of tiny bark beetles.
  • Adult beetles are very small, measuring only 1.5 – 2 mm long.
  • The beetle’s body is reddish-brown with 4-6 concentric rows of asperities (dot like ‘bumps’) on the prothroax (first segment on body).

What You Can Do

  • Learn how to properly identify the signs and symptoms of thousand cankers disease.

Resource Files


OFAH/OMNRF Invading Species Awareness Program. (2021). Thousand Cankers Disease. Retrieved from:
This factsheet may be reproduced for non-commercial purposes.

Header photo by Mary Ann Hansen,

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