Thousand cankers disease

Michigan black walnuts are threatened by the thousands cankers disease, although the disease is not yet present in the state .There are few black walnuts, but they are important and valuable component of many woodlots and cities in the southern counties.

Thousand cankers disease (TCD) is a combination of a native twig beetle and an exotic fungus. Beetles introduce fungal spores during their normal course of tunnel construction. The fungus kills live tissue under the bark. A single black walnut may have many beetle entry wounds, each infected by the fungus, thus the name “thousand cankers disease”. The cankers interrupt the flow of fluids and eventually kill the tree,

Suspect twigs will have slightly sunken spots, often darker than the surrounding area. If the bark is scraped away, dark ovals on light-colored healthy tissue suggest TCD. In the center of the canker, a small hole or dark spot might be present.

The cankers might be more difficult to see on branches and limbs but they will likely be present. More advanced cases of TCD infection will have many of these cankers, making them easy to find. And, naturally, avoid moving firewood around!

In a more general view, the black walnut may show crown dieback, which can, of course, be caused by a number of things. However, further investigation may be warranted to learn if TCD is the cause.

TCD is not known to affect other species of “Juglans”, such as butternut. Butternut has its own problems. TCD has made the jump from western states, across the Great Plains, and has been found in several eastern states. The beetle was found in Indiana this past spring.

Most new infestations are found by non-professionals who are curious about tree health and stay informed about tree threats, such as the TCD. In Michigan, the “Eyes on the Forest” project is designed to help citizens learn about and find new infestations of particularly harmful exotic species.

Michigan State University Extension recommends to look out for this disease. Should anyone believe they’ve seen TCD, it should be reported. Reports can be made on the MISIN website or through the Michigan Department of Agriculture and Rural Development (MDARD). People can also contact their county conservation district, most of which are informed about the TCD and other exotic species threats. 

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