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THOUSAND CANKERS DISEASE THREATENS TENNESSEE BLACK WALNUTS
Knoxville, TN
Thousand Cankers Disease may have started infecting Black Walnuts in the western U.S., but it is in Tennessee now. The question now is can it be contained? Currently there are no fungicide treatments available to cure or prevent Thousand Cankers Disease and it is almost always fatal to a Black Walnut once it is infected. Tree spraying to control the insect vector, the Walnut Twig Beetle, isn’t a promising solution either because the beetle is active during most of the growing season.
The Walnut Twig Beetle is a native insect to the western U.S. and Thousand Cankers Disease may be a native disease as well. The disease doesn’t cause significant harm to Arizona Walnuts, but Black Walnuts are extremely susceptible to the disease. Once Black Walnuts were planted out west the beetle, along with the disease, was able to infect Black Walnuts. The final step to make this a potential crisis for Black Walnuts in their native range was the transportation of infected wood from the western U.S. to the eastern U.S.
Walnut Twig Beetles are very small - about the size of the letter “i” on a Liberty dime. The insect tunnels into the cambium of the tree and carries disease spores with it. The disease causes a canker to form which inhibits the flow of water and nutrients in the tree. The Walnut Twig Beetle may have three generations in one growing season and as many as 30 beetles can develop under a single square inch of tree bark. It takes about three years for enough cankers to form to kill a Black Walnut.
Thousand Cankers Disease is not visible from the outside of a Black Walnut tree. The first sign that a Black Walnut might be infected with Thousands Canker Disease is yellowing leaves and a thin canopy. Dead leaves often stay on the tree instead of falling off. As the infection progresses individual branches will begin to die starting at the top of the tree.
To slow, or prevent, the spread of Thousand Cankers Disease avoid moving tree logs or firewood. Buy campfire wood locally and burn it all or leave it at your campsite. Wood from trees that have been cut down should be left on site.
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