Experts Watching for Tiny Beetle That Threatens Walnut Trees
Iowa tree and bug experts are looking for the presence of a beetle that could cause problems with Iowa’s valuable black walnut industry.
Thousand cankers disease is specific to walnuts and has been confirmed in Arizona, California, Colorado, Idaho, New Mexico, Oregon, Utah, and Washington in the 1990s. Recently, the disease has been confirmed in Pennsylvania, Tennessee and Virginia. It has not been found in Iowa.
The disease is introduced into a tree by the walnut twig beetle that carries a fungus on its body. The plant pathogen is spread under the bark of walnut trees when the beetle creates its extensive galleries.
Multiple feeding sites inoculate the fungus in multiple places along branches, which causes cankers to develop, enlarge and coalesce to completely girdle each affected branch.
The tree dies within three to five years of showing symptoms, although the first damage may have occurred a decade before symptoms developed.
Tivon Feeley, forest health program leader with the Iowa Department of Natural Resources, said special traps specifically targeting walnut twig beetles have been placed all over Iowa near state parks, county parks, sawmills, and in communities.
The traps contain a pheromone card to attract the beetles. Once inside, the beetles die. The samples are examined for the presence of the walnut twig beetle. He said the traps are noticeable and that to prevent losing any insect samples, he asked that they be left alone.
Funding to conduct the surveys for the walnut twig beetle and thousand cankers disease is being provided by the Iowa Legislature through the Iowa Forest Health Initiative and from the U.S. Forest Service.
“Walnut twig beetles are really small and if someone would open one of these traps, we will likely lose any samples collected,” he said. Samples will be examined and any potential walnut twig beetles will undergo further testing looking specifically for the fungus.
“This is only a precautionary step. We have not found a walnut twig beetle in Iowa at this time, and it is important to note that not all beetles carry the fungus,” Feeley said.
“This is another example of why we say don’t bring in wood from out of state.”
The Iowa Department of Natural Resources is working with the Iowa Department of Agriculture and Land Stewardship, Iowa State University Extension and Outreach and the U.S. Forest Service.