Thousand cankers disease, caused by an interaction of the walnut twig beetle (Pityophthorus juglandis) and a fungus (Geosmithia morbida), is a threat to the health of eastern black walnut. Thousand Cankers Disease is eliminating black walnut along the Front Range of Colorado and poses a grave risk to this species in its native range in eastern North America should the insect/ Geosmithia complex be introduced.Īccepted for publication. The species is also important for nut production, wildlife habitat, riparian buffers, windbreaks and other ecosystem services. A second pathogen, Fusarium solani, was isolated from the margins of elongate trunk cankers during the final stages of decline, but not from cankers surrounding beetle galleries.

We propose the name Thousand Cankers to describe this disease because mortality is the result of bark necrosis caused by an enormous number of coalescing branch and trunk cankers. This is the first report of Geosmithia as a pathogen of black walnut. They have 4-6 concentric ridges on the upper surface of the pronotum. Identification: Adult beetles are very small (1.5 2.0 mm in length) and is three times long as it is wide. Not a great deal is known about the beetle’s life cycle, but it is believed that two or more generations may develop per growing season in warmer areas. juglandis and this insect introduces the fungus into healthy trees during gallery formation. Walnut twig beetle (Pityophthorus juglandis) Description: This insect has currently not been found in the state of Michigan. The walnut twig beetle (WTB) is a small bark-boring beetle (Pityophthorus juglandis) believed to be native to the southwestern US. Geosmithia was consistently recovered from the bodies of P. We report that this mortality is the result of a combination of an expanded geographic range of the walnut twig beetle ( Pityophthorus juglandis), its aggressive feeding behavior on black walnut, and extensive cankering caused by an unnamed Geosmithia fungus associated with the beetle.

Affected trees initially show a yellowing and thinning of leaves in the upper crown, followed by twig and branch dieback and ultimately tree death. Since 2001, widespread mortality of black walnut ( Juglans nigra) has been reported in Colorado, USA.