A new and deadly disease is affecting black walnuts across the western United States. Thousand Cankers Disease (TCD) is actually an insect and disease complex. It is caused by a tiny insect, the walnut twig beetle (Pityopthorus juglandis), which carries spores from a Geosmithia fungus as it goes about its feeding and breeding activities. The fungus causes many small cankers, or dead spots, to form, hidden underneath the bark.
Eventually, the thousands of cankers coalesce and kill the main trunk of the tree.
For years, the walnut twig beetle was known only in the southwest where it fed on the twigs of the Arizona walnut. Because this walnut was resistant to the Geosmithia fungus, the beetle only damaged small branches and caused little damage to the tree itself. But beginning in the late 1990s, the walnut twig beetle expanded its range and is now found in several western states. As the beetle colonized new areas, it found black walnut that had been planted in many locations beyond its native range.
The Geosmithia fungus the beetle carried is deadly to black walnut, and to make matters worse, the beetle began attacking the main trunk of black walnut trees, resulting in death. TCD is also established in California walnut orchards.
K-State Research and Extension, the Kansas Forest Service and the Kansas Department of Agriculture are working on plans to keep this disease from becoming established in the state. The walnut industry in the eastern United States is also concerned that Kansas could serve as a gateway to the spread of this devastating disease to the rest of the country.
Quarantines will likely be developed in the coming months, said Charles Barden, extension forester at Kansas State.