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    Thousand Cankers Disease (TCD) is caused by a fungus (Geosmithia morbida) that is vectored by a bark beetle, the walnut twig beetle (WTB), Pityophthorus juglandis (Coleoptera: Curculionidae: Scolytinae). The disease was first recognized in 2008 and has caused the widespread death of walnut trees (Juglans sp.) throughout eight western states. As the beetle bores into a walnut tree to feed and reproduce, it infects the bark tissue with the fungal pathogen. G. morbida is considered a weak plant pathogen and requires a vector to become established. It appears that only mass attack by the beetle is sufficient to introduce enough pathogen to kill a tree. In the early stages of TCD, small cankers develop around the galleries of colonizing beetles. As the disease progresses, cankers become more diffuse and coalesce, interrupting the nutrient-conducting tissues of the tree and eventually killing the inner bark of affected branches and stems.

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    Ginzel, Matthew; Juzwik, Jennifer. 2014. Geosmithia morbida, the causal agent of thousand cankers disease, found in Indiana. HN-89-W. West Lafayette, IN: Purdue Extension, Department of Entomology. 2 p.

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