A fungus found in some Eastern and some Western states could be devastating to Missouri’s vital black walnut industry, if it were to make its way to this state.

A fungus found in some Eastern and some Western states could be devastating to Missouri’s vital black walnut industry, if it were to make its way to this state.

Nate Forbes, forestry district supervisor, Missouri Department of Conservation (MDC), Neosho, said Thousand Canker Disease affects walnut trees and the walnut family.

“That could be our native Missouri black walnut, but also European walnut or carpathian,” Forbes stated.  “Even the lesser known butternut can get it, which is considered the white walnut.”

Forbes reported that the fungus is known to exist in eight Western states and to the east it has been detected in Maryland, North Carolina, Ohio, Pennsylvania, Virginia, Tennessee. It was found in Indiana just last month.

“It’s something we’re concerned about,” said Forbes. “Because Missouri has the bulk of the walnut in the U.S. Out of all the United States, the next closest state has not even half the amount of walnut that Missouri produces. We’re the largest walnut producer in the U.S. and it’s of grave concern to us.”

Until recently, Forbes said scientists had determined the vector that transfers Thousand Canker Disease from tree-to-tree is the little walnut twig beetle, a native insect found in the Western United States.

“This is a very tiny beetle, it’s not even as big as a pencil lead, it’s very small,” he said. “In Indiana recently, there was no evidence of the walnut twig beetle but actually another small beetle — a type of weevil — was found exiting some sick trees. They tested the weevils and found this on those, so that’s kind of a new development.”

Forbes talked about the small beetles.

“These small beetles will tunnel inside of a tree and the spores of the fungus get caught on their little minute hairs,” he said. “Then, as the beetle emerges from the tree it may fly around, mate with another beetle, and then bore into another tree — it carries the spores into that new tree. Typically that’s the way this is thought to have been spread in the wild. A big concern of ours is the movement of untreated wood, whether that’s firewood or the wood that woodworkers use.”

Forbes reported that you can find of slabs of walnut on the Internet and if it still contains the bark, beetles could be hiding underneath.

He continued, “So if somebody is selling untreated wood — that’s not been heat-treated — and they’re selling it across state lines, there’s a potential for this disease to move overnight from one state to another. Whereas the natural progression of this disease would take years, years and years, probably.”

Forbes said most Southwest Missouri sawmills get most of their raw walnut from this state, but also process some wood from Oklahoma, Arkansas and Kansas. He said the transport of wood across state lines is a concern and none of those states are quarantined for Thousand Cankers Disease.

“So right now,” Forbes said, “I guess there’s nothing stopping wood products in unfinished form from traveling across the state lines, at least not with this disease.”

He said state quarantines do not allow the transport of firewood across state lines in an attempt to limit the emerald ash borer.

When Thousand Cankers Disease strikes a walnut tree, Forbes said a wilting of the leaves occurs from the ends of the branches in a die-back.

“They may first turn yellow or chlorotic-looking,” he explained. “(Then) as they yellow, they turn brown and wilt. It looks like its coming from the top down and the outside of the branches in toward the main trunk.”

Forbes said the time to look for the disease’s symptoms is in July or early August.
He said the outcome for a walnut tree after becoming infested with the disease is death.

“They call it ‘Thousand Cankers,’ because there’s all these tiny little cankers that form underneath the bark wherever these beetles were occurring,” he said. “The cankers grow together and they disrupt the flow of nutrients and water inside the tree. They essentially girdle the tree from the inside out.”

He said black walnut trees usually die within three years after initial symptoms are observed.
Forbes said those symptoms do not mean that a tree has Thousand Cankers Disease, as trees that are planted on a poor growing site or that experience other adverse growing conditions may also look the same.

“Whether it’s the environment or even the planting site, or even a couple of summers of drought, sometimes that kills off our trees, too, from the top down,” he said. “So just because a walnut tree looks sick doesn’t necessarily mean that it has this.”

If Thousand Cankers Disease were to arrive in Missouri, it could be devastating. Forbes said wood products is a more than $4.5 billion industry in the state, and walnut is a significant portion of that.

He noted, “Walnut is one of our most valuable wood species in Missouri, so a disease like this that could kill off a lot of the trees would have a significant economic impact.”

Forbes said another canker disease is affecting some oak trees in Missouri. He will explain the symptoms and the problems associated with Hypoxylon Canker in a future edition of the Neosho Daily News.

He welcomes any concerned landowners to bring pictures or leaf samples to the MDC Neosho office so he can try to help determine what is happening to their tree.

Call the office at 451-4158.