Eastern Walnut Trees Under Beetle Threat

U.S. forests are under attack from well-publicized pests such as the emerald ash borer and the pine beetle, and now yet another deathly beetle is on the rise. On Aug. 9, authorities confirmed the presence of Thousand Cankers Disease in black walnut trees in Bucks County, Pa. The disease was first described in the Western U.S. in the '90s. Then, in 2010 it was found in Tennessee, and earlier this year it was found in Virginia.

The disease is caused by the walnut twig beetle. During its larva stage, it eats the tree's cambium, which creates tunnels between the outer bark and wood, according to John Kirksey of Tennessee's Department of Agriculture, Division of Forestry. "There is much to learn about the walnut twig beetle," Kirksey added.

These walnut tree cankers are brought on by fungus from the walnut twig beetle. Credit: Whitney Cranshaw, Colorado State University.

Over time, repeated beetle attacks cause internal cankers that disrupt the flow of water and nutrients throughout the tree. This leads to dieback of branches and-within about 10 years-kills the tree. At stake is Pennsylvania's $25 billion hardwoods industry, according to the Pennsylvania Department of Agriculture.

In response to the disease, the Pennsylvania Department of Agriculture ordered a quarantine Aug. 10, restricting the movement of walnut material that has not been processed, i.e., kiln dried and free of bark. The quarantine also restricts the movement of walnut material and hardwood firewood from states known to have Thousand Cankers Disease, including Arizona, California, Colorado, Idaho, Nevada, New Mexico, Oregon, Tennessee, Utah, Virginia and Washington.

Article updated Sept. 1.