Thousand Cankers Disease in Tennessee Walnut Trees

On July 27, I posted a short entry about Thousand Cankers Disease (TCD), a twig beetle-born fungus that has been killing black walnut (Juglans nigra) trees in seven Western states. Yesterday, I read in a press release from the Department of Bioagricultural Sciences and Pest Management at Colorado State University, that the disease has been potentially identified in Tennessee, within the native range of the Eastern black walnut. While the USDA has not yet issued confirmation, officials in Tennessee expect word by the end of the week.

TCD has already killed thousands of trees in the West, and if it spreads in the Eastern black walnut’s native range, it could be devastating. “Based on our experience here in Colorado, TCD will be difficult, if not impossible, to stop,” wrote Ned Tisserat, extension specialist and professor of plant biology at CSU, in the release. “I believe that there are probably other outbreaks in the East that have not yet been noticed,” he wrote, and urges people to be on the lookout for unusual dieback of walnut trees, particularly in urban areas, as firewood and fresh lumber are the likely carriers.

Whitney Cranshaw a professor of entomology and extension specialist at CSU, wrote in an e-mail that while the J. nigra, a non-native species in the West, is most susceptible to TCD, other species are affected as well.

Tisserat told me via e-mail that the beetle and fungus live in the bark of the walnut tree, and that the wood can still be used for woodworking. But, “It is critical that it be debarked and kiln dried before moving it to new locations” to help arrest the spread of TCD.

And though the fungus is killed in the kiln-drying process, it has not been determined if allergic reactions, similar to what some woodworkers experience when using spalted wood, could occur.

“The beetle that carries the fungus only lives in the bark, not the wood,” wrote Tisserat. “Therefore, the wood itself is not damaged from the disease and can still be used for woodworking.” “It is critical that the wood be debarked and dried before moving it to new locations.” “If the wood is kiln dried and debarked, it should be safe. But we must prevent the movement of fresh wood.” No research has yet been conducted on air-dried wood.

As yet, there is no federal quarantine on walnut, but Steven Seybold, a research entomologist with the U.S. Forest Service, says that several states have instituted a ban on importing walnut from the west.

The twig beetle that carries the fungus is native to the West, and the J. nigra species , the walnut most suceptible in the West to the diesease , is not. So, “it’s a little bit of an unknown how this twig beetle will behave in our Eastern forests,” said Tom Womack, a spokesman for the Tennessee Department of Agriculture.

The primary message for now to help arrest the spread of TCD: Don’t move walnut unless it’s been debarked and kiln-dried.

– Megan Fitzpatrick