Eastern Black Walnut Trees Plagued by More Than Thousand Cankers Disease
Thousand cankers disease, characterized by decline and dieback in tree crowns, can lead to tree mortality of high-value eastern black walnut; however, other bark and wood-infesting insects and canker fungi can also cause dieback and death in the species. Forest Service scientists, in collaboration with colleagues from the University of Missouri and Purdue University, used stem-girdled trap trees as a detection method for the walnut twig beetle and then determined what other insect pests and fungal pathogens colonized stressed walnut. More than 16,000 bark and ambrosia beetles were collected from sampled portions of 106 study trees in 15 Indiana and 12 Missouri sites. Most of these were non-native, ambrosia beetles. The granulate ambrosia beetle, the black stem borer, and the fruit-tree pinhole borer were the most abundant. The first two species attack and kill stressed black walnut. A subset of the collected insects was assayed to determine the fungal species associated with each predominant insect species. Although the Thousand Cankers Disease fungus was not isolated, several other reported fungal pathogens and other species were. A related Geosmithia pallida fungus was detected on the granulate ambrosia beetle and fruit-tree pinhole borer, but it is not considered a pathogen of walnut.
|Bark and ambrosia beetles and their associated fungi colonizing stressed walnut in Missouri and Indiana||(publication)|
Forest Service Partners