Thousand cankers disease (TCD) is caused by a fungus (Geosmithia morbida) carried by the walnut twig beetle (WTB; Pityophthorus juglandis). The fungus and beetle only infest walnut trees; the adult beetle constructs galleries in the phloem, where the fungal spores are introduced. Small cankers then form around the galleries, girdling the branches. The walnut twig beetle is native to Arizona, California, and New Mexico; however the beetle and fungus have been found in eastern states. In 2012 the fungus was found in Butler county, Ohio.
Adult beetles are small, approximately 1/16 inch long, and reddish-brown. Visually inspecting walnut trees for dieback is currently the best survey tool for detecting the disease. Symptoms of TCD vary, but commonly include thinning crowns, yellowing or wilted leaves in the crown and limbs that died recently.
The quarantine prohibits anyone from removing regulated materials from Butler County. Regulated materials include walnut nursery stock, unprocessed walnut lumber, or any other walnut material, such as logs, stumps, roots, branches, mulch, wood chips, and any firewood.
The quarantine does not apply to nuts, nut meats, hulls, processed lumber (bark-free and kiln-dried) and finished wood products without bark, such as walnut furniture, instruments and gun stocks.
Damage and Impact
Thousand Cankers Disease (TCD) primarily affects black walnut trees, as well as other species of walnut. The initial symptoms are yellowing and crown dieback, followed by cankering and rapid leaf wilt. The fungus causes circular cankers under the bark; the surface may have no visible symptoms. Heavily infested branches may have a dark stain directly above the canker. Infected trees typically die within 3-5 years. There is no known treatment for TCD.