Walnut Twig Beetle & Thousand Cankers Disease

Author(s): Laurie Stepanek
Wednesday, April 15, 2020
Walnut Twig Beetle under a microscope.

The Nebraska Department of Agriculture announced May 14th that walnut twig beetle, a carrier of a fatal disease of walnut trees, was discovered in Nebraska. This is the first confirmed detection of the beetle in the state.

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What is the Walnut Twig Beetle?

Removing beetle from infested tree
Thousand cankers disease has killed walnut trees throughout the western United States over the past two decades. Photo courtesy: Karen Snover-Clift, Cornell University, Bugwood.org

Walnut twig beetles are tiny brown insects that feed under the bark, causing twigs to die.

“The walnut twig beetle actually is not a serious pest,” said Rachel Allison, Western Forest Health Specialist for the Nebraska Forest Service.

“The problem is the beetles often carry fungal pathogens on their bodies, which can infect the trees they feed on. The resulting disease, known as ‘thousand cankers disease,’ causes trees to decline and die.”

Thousand cankers disease has killed walnut trees throughout the western United States over the past two decades. It was particularly devastating in the communities along the Front Range of Colorado, the majority of black walnut are now gone. The only walnut species native to Nebraska, the eastern black walnut, is highly susceptible to the disease. In addition to its use for timber, nuts and wildlife habitat, black walnut is commonly planted in community and rural landscapes.

Identifying Thousand Cankers Disease

Diseased trees initially exhibit yellowing foliage, followed by brown wilted foliage, branch dieback and tree death. Tree death occurs two to three years after initial symptoms appear.

“No diseased trees were identified in Gering,” Allison said. “However, trees may be infected for many years without visible symptoms.”

The twig beetles were captured in detection traps placed near walnut trees at the Monument Shadows Golf Course in Gering by Nebraska Department of Agriculture as part of their annual walnut twig beetle survey. More intensive detection efforts will be conducted in the coming weeks.

Nebraska Walnut Quarantine

The Nebraska Department of Agriculture implemented a quarantine prohibiting the movement of walnut wood into Nebraska in 2010. The walnut twig beetle and canker fungus are easily moved long distances in diseased wood. Regulated material includes walnut branches, logs, roots, firewood, green lumber, bark, wood chips and nursery stock. At this time there are no treatments available to control diseased walnut trees.

Restrictions on Moving Walnut
Walnut Twig Beetle
Image Courtesy: Steven Valley, Oregon Department of Agriculture, Bugwood.org