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Missourians should be aware of black walnut quarantine


Robert E. Thomas
Information Specialist
University of Missouri Cooperative Media Group
Phone: 573-882-2480

Photo available for this release:

Walnut twig beetles boring under bark bring a fungus that causes these dark cankers in black walnut trees.

Credit: Whitney Cranshaw, Colorado State University,

Published: Tuesday, May 18, 2010

Story source:

Michele R. Warmund, 573-882-9632

COLUMBIA, Mo. – While thousand cankers disease has not yet hit the state’s black walnut industry, Missourians should take to heart the recent emergency quarantine issued for black walnut by the Missouri Department of Agriculture, said a University of Missouri Extension horticulturist.

“Everyone from commercial producers to the casual wood hobbyist should be aware of the quarantine and the damage that could result should the disease reach the state,” said Michele Warmund.

Thousand cankers disease has devastated black walnut trees in at least nine western states: Washington, Oregon, California, Idaho, Utah, Arizona, New Mexico, Nevada and Colorado. According to Missouri Department of Agriculture estimates, the disease could cost the state more than $850 million in losses over a 20-year period.

All walnut nursery stock, budwood, scionwood, green lumber, firewood and other living or dead plant material from those states is now prohibited in Missouri. This includes logs, stumps, roots, branches and composted and uncomposted chips.

Exceptions to this quarantine include nuts; kernels; hulls; bark-free, kiln-dried lumber with square edges; and finished wood products without bark, including walnut furniture, instruments and gunstock.

Any plant material or articles transported into Missouri in violation of the quarantine may be destroyed or returned to the point of origin. Penalties will be imposed on carriers of regulated material.

The disease is caused by a fungus that attaches to walnut twig beetles. These tiny bark beetles inflict very little damage themselves. The fungus, however, creates small patches of dead tissue under the bark. As these cankers grow and merge, nutrients can no longer move through the tree, killing it in one to three years.

“The first symptoms of the disease are leaf yellowing and branch dieback in the upper part of the tree,” Warmund said. “Limb mortality occurs and eventually the whole tree dies.”

The current emergency quarantine will expire in January. The development of a longer-term ruling is underway.

More information on the disease is available at