Kansas Taking Stand Between Tree-Killing Disease, Eastern U.S. Walnuts

MANHATTAN, Kan. – Its location has now placed Kansas in a position of both risk and responsibility for a natural resource.

As one result, Kansas Secretary of Agriculture Josh Svaty signed a state quarantine this week. Its purpose is to deny entry to a new and deadly black walnut disease – one that already has spread into every state west of Kansas except for Nevada, Montana and Wyoming.

“We didn’t even have a name for it two years ago. But, Thousand (1,000) Cankers disease has killed more than 2,000 black walnut trees in Denver alone. Boulder and Colorado Springs basically don’t have walnuts anymore,” said Bob Atchison, rural forestry coordinator with the Kansas Forest Service (KFS).

That’s not even close to the damage the disease could cause, however, if it gets into Kansas, the forester said. Although the state is in the middle of the great American prairie, Kansas also is a gateway to the hardwood forests that extend from the Plains to the Atlantic Ocean.

“Up to now, Thousand Cankers has just been killing park and street trees – ones that people have bought or brought in and planted,” Atchison said. “Kansas is the western-most state where black walnuts are native trees. If we can’t keep the gate closed – keep this disease out of our state — the result could be catastrophic on a national level.”

Like the elm trees felled in the past by Dutch elm disease, black walnuts can be a beautiful shade tree, said State Forester Larry Biles.

“In states like Kansas, though, black walnuts are the heart of our forest products industry. They’re the most economically important tree species we’ve got,” Biles said. “They’re also an important part of our state’s ecological balance, providing food and shelter for Kansas wildlife. The native ones tend to grow where they also help protect the quality and quantity of our state water supplies.”

Because Thousand Cankers is something new, black walnut trees have no built-up immunity or resistance to it. And, scientists have yet to find ways to prevent or cure it.

“Until they do, quarantine is our only real hope,” the state forester said. “But, a quarantine will work only if people understand the need for it and volunteer to cooperate. If just one person carelessly brings in an infected piece of Colorado firewood, that could spell the end of the U.S. black walnut as we’ve known it.”

Researchers at Colorado State University have found 6×18-inch logs containing up to 30,000 of the walnut twig beetles (Pityophthorus juglandis) that transport the disease. The average 90 beetles per square inch weren’t obvious at first, and the logs didn’t look infested. To see the pests, the scientists had to strip the logs and use magnification.

Walnut twig beetles leave a hole the size of a pin prick when they enter the hidden part of their lifecycle, both living and eating under walnut tree bark.

“The pest’s original range was in our southwestern states and parts of Mexico. It attacks the native walnuts there, but doesn’t have much of an economic or environmental impact,” Atchison said. “We may never know why it recently decided to expand its territory and move north.  Perhaps global warming played a part. In any case, a fungus – a new form of Geosmithia – came along for the ride. And, now that fungus is killing black walnuts.”

While twig beetles create extensive galleries of tunnels – which is damaging enough – their passenger fungus colonizes around the galleries, killing tree tissue. The brown-black blotches of dead cells that result are several times bigger than any tunnel. They’re the cankers that give the disease its name.

“We suspect it takes a while for this pest partnership to expand enough to girdle and kill an entire tree,” Atchison said. “Until then, the only signs the tree is dying may be the occasional lost branch and some leaf wilt that just keeps getting worse.”

The typical progress of the disease makes tracking its spread from location to location difficult.

For more than a year, however, experts from the Kansas Department of Agriculture, Kansas Forest Service, and Kansas State University Research and Extension have been working together to monitor for any signs of Thousand Cankers or its carrier. They’ve begun hosting pest detector workshops, as well, to help Kansans prepare. Their next workshops will be in Emporia, Hays and Garden City this fall.

State Forester Biles said what’s at risk in Kansas alone is more than 26 million black walnut trees, the current roles they play and an economic potential worth millions. But, the success of the quarantine will determine whether the prairie state will have a future that continues to include an important natural resource.

The official Kansas quarantine is available online at www.ksda.gov/plant_protection/content/360/cid/1704. The KDA news release about the quarantine is at http://www.ksda.gov/news/id/339.

Source : K-State Research and Extension

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