In May 2008, walnut mortality observed in Colorado as early as 2003 was attributed to numerous cankers developing in association with insect galleries. The new disease complex is referred to as “thousand cankers disease” (TCD) and is considered to be native to the United States.
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. 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.
Various states conducted surveys in 2011, resulting in the detection of TCD in Pennsylvania and Virginia. Surveys in 2012 revealed TCD in North Carolina.
There is no federal regulation in place for TCD. In 2010, APHIS reviewed the geographic distribution of the known TCD-affected areas, considered its potential to become established throughout the United States, and assessed the effectiveness of available regulatory tools. The conclusion was that a Federal regulatory framework would have little long-term impact on the spread of TCD. This is due to the challenges of regulating the long-distance movement of an array of products and shippers, poor detection capability, and the apparent broad geographic distribution of TCD in the United States. However, APHIS does have regulations in place that address some of the known TCD pathways, including requirements for the importation of solid wood packaging and propagative material. APHIS also has other ongoing efforts to mitigate forest pest threats from the interstate movement of firewood, which is another pathway for the spread of TCD. In addition,several states have set up exterior quarantines. For further information about a specific state’s quarantine, please contact the State Department of Agriculture.
Pest and Disease Identification
Pest and Disease Management
National Policy Manager