Thousand Cankers Disease (TCD ) results from the combined activity of a fungus, Geosmithia morbida, and the walnut twig beetle (WTB), Pityophthorus juglandis. TCD was originally described from scattered locations throughout western states. Now it appears that walnut twig beetle (WTB) and, by association, TCD, is present wherever susceptible walnut species grow in the west. In July 2010, TCD was reported in Knoxville, Tennessee, causing dieback on black walnut. The Tennessee infestation is believed to be at least 10 years old. This was the first report east of the 100th meridian, raising concerns that large native populations of black walnut in the eastern United States may suffer severe decline and mortality. We do not know the true distribution of this insect/disease association across the United States. While TCD has caused dieback and mortality across various climatic zones and among several walnut species, the extent of risk and impact to black walnut within its native range is still unknown.
Black walnut is a significant economic, social and environmental resource, and appears to be highly susceptible to TCD. Laboratory and field research with G. morbida have shown that all walnuts and butternut show significant amounts of dead bark tissue in response to controlled inoculations of the pathogen. The survival of butternut is already seriously threatened by butternut canker. The only other known host for WTB and G. morbida is wingnut (Pterocarya spp.)