Thousand Cankers Black Walnut Disease

General Information

Species Name: Geosmithia morbida

Also Known As: Thousand cankers disease, TCD

Pathogen Type: Fungus

Organisms Affected: Walnut trees

Transmissible to Humans: No

Why is it a Concern? 

TCD has killed thousands of walnut trees in the United States since its identification in 2008. While several walnut trees are susceptible to TCD, black walnuts are particularly susceptible. Trees will die over several years after being infected with TCD. 

How is it Spread? 

TCD is spread by walnut twig beetles. The beetles gnaw into walnut trees to feed and reproduce, transmitting TCD while doing so. The transport of beetle infested trees and wood can spread TCD. 

TCD is present within the western United States. The walnut twig beetle was identified in Nebraska in 2024. 

Symptoms

Small Cankers

Small round or oblong cankers may occur on the outer tree bark where tree material is dying. Dark amber staining or cracking in the bark may or may not occur above the canker. 

Dead Branches

Leaves and foliage may turn yellow, become brown, and branches may die off. 

Beetles

Beetle exit holes and galleries may be present on dead and dying branches.

Photos

Tree bark with damage revealing green wood and decay, pointed at by a black and red pen.
Tree bark showing green and brown discoloration from damage or disease.
Green tree leaves under a clear blue sky with a sparse, leafless tree in the background.
Dark, circular plant stem lesion with green branches and blurry background.

Prevention and Control

Mechanical

Prune affected branches and properly dispose of them to reduce the spread of TCD. Ensure you are maintaining healthy trees with proper watering, fertilization, and pest management to reduce tree stress, therefore reducing susceptibility to TCD. 

Cultural

Transporting firewood can accidentally facilitate the spread of TCD and other invasive species. Don't move firewood and burn it where you buy it. 

Chemical

Please refer to the 2026 Guide for Weed, Disease and Insect Management in Nebraska.

What to Do if You Suspect TCD

If you suspect a tree on your property is infected by TCD, contact the Nebraska Department of Agriculture or Nebraska Forest Service. You can also report sightings to the Nebraska Invasive Species Council. 

References and More Information

Backyard Farmer

Colorado State University Extension

Missouri Department of Conservation

National Invasive Species Information Center

Nebraska Forest Service

Pennsylvania Department of Agriculture

USDA Animal and Plant Health Inspection Service

University of California Statewide Integrated Pest Management Program