TCD results from the combined activity of Geosmithia morbida fungus and the walnut twig beetle (WTB, Pityophthorus juglandis). The WTB has expanded both its geographical and host range over the past two decades, and, coupled with Geosmithia morbida, walnut mortality has occurred in California, Oregon, Washington, Idaho, Utah, Arizona, New Mexico, and Colorado. In July 2010, TCD was first reported east of the 100th meridian in Knoxville, Tennessee. This raised concerns that large native populations of black walnut in the eastern United States may suffer severe decline and mortality. Therefore, surveys were conducted in various states in 2011, and TCD was found in Pennsylvania and Virginia.
Black walnut is a significant economic, social and environmental resource, and appears to be highly susceptible to TCD. Black walnuts exhibit little to no resistance to the pathogen and its vector.
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There is no federal regulation in place for TCD; however, several states have set up exterior quarantines. This includes, but may not be limited to, Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, North Carolina, Nebraska, Ohio, Oklahoma, Pennsylvania, Virginia, and Wisconsin. For further information about a specific quarantine, please contact the State Department of Agriculture.