Thousand Cankers Disease threatens Missouri black walnut industries

Sunday, September 12, 2010 | 4:48 p.m. CDT; updated 9:37 a.m. CDT, Monday, September 13, 2010
Thousand cankers disease is caused by a fungus that is carried by walnut twig beetles. The fungus spreads and blocks nutrients to the tree, eventually causing the tree to die. The disease has not been discovered in Missouri, but the state has a large native population of Eastern Black Walnut Trees.

COLUMBIA – Thousand Cankers Disease could cause walnut farmers in Missouri a thousand headaches if the invasive fungus makes its way from Tennessee to Missouri this fall.

The disease, which is carried by the twig beetle, was originally confined to states in the West, but foresters in Tennessee discovered infected trees in Knoxville in July. Before the discovery, Colorado was the easternmost state with reported cases of the disease.


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This discovery has special significance for Missouri, which according to a press release from MU, has more black walnut trees than any other state within the black walnut's natural range.

Thousand Cankers Disease can be identified by wilting leaves on black walnut trees that stay on branches near the canopy and spread down. By the time the first symptoms appear, the damage has been done and the tree dies.

The beetle that carries the disease only attacks the black walnut wood. The nuts are safe to move and eat.

John Tuttle, the forest products program supervisor of the Missouri Department of Conservation, said it would be "devastating" to Missouri's economy if the disease were to become an endemic.

According to a 2009 report co-authored by Tuttle, Missouri would lose more than $30 million annually in wood production alone, plus another $35 million in lost nut production.

Urban walnut trees would require expensive removal, landscaping and replacement bringing annual losses to about $65 million. The Conservation Department estimates a 20-year economic impact of more than $850 million if the disease becomes widespread in Missouri.

Hank Stelzer, who is a professor of forestry at MU, said, "It's not a matter of if it will happen here – it's a matter of when."

Puzzled by the rapid spread of the disease from Colorado to Tennessee, Stelzer said he suspected the trade of hobby wood and firewood over the Internet as the cause. He recalled the emerald ash borer, a similarly invasive species that also came to Missouri through firewood.

"Scientists have been able to isolate over 23,000 beetles in a single 2-foot log," Stelzer said.

The twig beetle, which carries the fungus, does not naturally migrate far.

"Instead," said David Hammons, director of marketing for Hammons Black Walnuts, "We have to worry about the 'unnatural' spread of the disease – that is, the man-made spread. The best thing we can do now is get the word out."

Hammons Black Walnuts shares information with hullers at each of its 250 hulling stations. The company also encourages its hullers to spread information about the disease with farmers they come in contact with.

"If you find an infected tree, call the department of conservation immediately," Hammons said. "Let them know where you found the infection, and follow what their recommendations are."

Despite the great risk the disease poses to Hammons' business, he feels confident in the ability of the state conservation and agriculture departments to handle this problem.

The Missouri Department of Agriculture issued a black walnut quarantine on April 12, barring all walnut nursery stock, budwood, scionwood, green lumber, firewood and other living or dead plant material from nine states: Washington, Oregon, California, Idaho, Utah, Arizona, New Mexico, Nevada and Colorado.

Missouri was the first state to issue a quarantine. Since then Nebraska, Michigan, Oklahoma, Kansas, Indiana and North Carolina have enacted similar quarantines.

"We want to see the public not bringing walnut wood from out of state into Missouri, especially not from a quarantined state,"  Tuttle said.

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