The thousand cankers disease that is killing black walnuts in eight western states, including California and the Davis area, has found its way across the Great Plains and east of the Mississippi River; it has just been detected in east Tennessee.
A pest alert, distributed by the U.S. Forest Service and co-authored by Davis-based researcher Steve Seybold, is sounding the alarm.
The Tennessee Department of Agriculture (TDA) announced the discovery of thousand cankers disease on Aug. 5 in Knox County. This is the first detection of the disease east of the Mississippi River. A DTA forester discovered its presence in July.
Seybold, research entomologist with the U.S. Forest Service, Pacific Southwest Research Station, Davis, and a faculty affiliate of the UC Davis Department of Entomology, says the disease symptoms to watch for are branch mortality; numerous small cankers on branches and the main stem of the tree; and the entry and exit holes of the tiny bark beetles.
The disease, caused by the walnut twig beetle (Pityophthorus juglandis) in association with a newly described fungus with the proposed name of Geosmithia morbida, occurs only on walnut species. Eastern black walnut is one of the most susceptible species. “An infested tree usually dies within three years of initial symptoms,” he writes.
Seybold believes the disease could already be introduced more widely in eastern forests due to the widespread distribution of susceptible eastern black walnut, the favorable climate, and the capacity of the duo of pests to invade new areas and survive.
As of Aug. 5, the disease has now been confirmed in nine states: Arizona, California, New Mexico, Colorado, Idaho, Oregon, Tennessee, Utah and Washington.
For more information on the disease, see http://entomology.ucdavis.edu/news/walnuttwigbeetle.html.