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Thousand Cankers Disease

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Canker on a Southern California walnut seedling. Curtis Utley, CSUE,

Bugwood.org

Thousand cankers disease (TCD) ravages black walnut trees, which are recognized

as some of the rarest, most valuable hardwoods in North America. The disease is

caused by a harmful fungus (Geosmithia morbida) spread by walnut twig beetles (
Pityophthorus juglandis).

As they gnaw into trees to feed and reproduce, small, cankerous-looking wounds

develop on branches and trunks. Cankers swell as the disease progresses, disrupting

plant tissue and eventually killing the inner bark of affected branches and stems.

TCD was identified in 2003, and since then, has decimated millions of black walnut

trees in California, Oregon, Washington, Idaho, Utah, Arizona, New Mexico, and

Colorado.

What To Look For

There are three major symptoms that indicate a black walnut tree has TCD. Here's

what to look for:

Dead branches

The earliest symptom is yellowing foliage that progresses rapidly to brown

wilted foliage, then finally to branch mortality.

Small cankers

The harmful fungus causes distinctive circular to oblong cankers on the

outer tree bark, which eventually kill plant tissue. The surface of the bark

may have no symptoms, or a dark amber stain or cracking of the bark may

occur directly above a canker.

Bark beetles

Tiny entrance and exit holes may be visible on dead and dying branches.

Bark beetle galleries, patterns left by the insects, are often found in

multiple layers within the cankers in the vascular tissue. In the final stages

of disease, even the main stem may exhibit beetle attacks and cankers.

Report Plant Pests and Diseases

Have you seen this pest or signs of pest damage? Immediately report your findings.

Find your State plant regulatory official

Find your State plant health director
Controlling Thousand Cankers Disease

APHIS' Response

There isn't a Federal regulation in place for TCD. In 2010, APHIS reviewed the

geographic distribution of the known TCD-affected areas, considered its potential to

spread across the nation, and assessed the effectiveness of a regulatory framework.

The conclusion: Federal regulations would have a minimal long-term impact on the

spread of TCD because of poor detection capability, challenges regulating the longdistance movement of products and shippers, and the broad geographic distribution

of TCD in the United States.

To address some of the known TCD pathways, APHIS has implemented requirements

for importing solid wood packaging and propagative material. APHIS also has other

ongoing efforts to mitigate forest pest threats from the interstate movement of

firewood, which is another pathway for the spread of TCD. In addition, several States

have set up exterior quarantines. 

Thousand Cankers Disease Survey Guidelines (2022)

National Response Framework for Thousand Cankers Disease (TCD) on Walnut

USDA-APHIS-PPQ Pathway Assessment: Geosmithia sp. and Pityophthorus

juglandis Blackman movement from the western into the eastern United States

Contact Us

William Wesela

National Policy Manager

Email: william.d.wesela@usda.gov

Phone: 301-851-2229