A Technical Report from The Bartlett Tree Research Laboratories
Thousand Cankers Disease (TCD) is a fatal disease affecting several types of walnut trees (Juglans spp.) with significant mortality observed in black walnut (Juglans nigra). Walnut trees become infected by TCD as a result of the boring activity of the walnut twig beetle (Pityophthorus juglandis) which spreads a fungus, Geosmithia morbida, to susceptible hosts. The fungus is weakly pathogenic, and it takes many beetle attacks to eventually kill trees. Although extensive black walnut mortality has been reported in the western U.S. since the 1990s, it has only recently been associated with this beetle-fungus complex.