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Thousand Cankers Disease – Still Much Ado About Nothing

Walnut Twig Beetle

Thousand Cankers disease is carried by the Walnut Twig Beetle (shown above)

When tree or other plant damage is imminent, I will be the first to tell you about it. But, I won’t use scare tactics or try to sell you treatment for insects and diseases that might come some day. A disease called thousand cankers falls into that category.

I have begun to hear rumors of its arrival here in upstate New York, but I haven’t really seen anything to support that.

Thousand cankers is a disease that affects members of the walnut family. It was first discovered in the west, and Dr. Whitney Cranshaw, a professor at Colorado State University is one of the authorities on the subject. I first heard of his research back in 2009.

Dr. Cranshaw explained that the fungal disease is carried by a little insect called the walnut twig beetle. When an insect carries a disease, it is called a vector. Thousand cankers was killing black walnut trees in the west. Dr. Cranshaw blamed that on the fact that black walnuts are eastern trees that were introduced to the west. He predicted that the disease would eventually come east, but that our black walnuts would be able to resist it. He was right so far. Like so many other landscape pest problems, the infected walnut twig beetle hitchhiked east aboard black walnut logs purchased by eastern craftsmen. Black walnut is a valuable, sought-after species of hardwood for such products as furniture.

Thousand cankers has been identified in Pennsylvania, Tennessee and Virginia but not here. Here in the Rochester area, we have seen a similar disease in less valuable butternut trees. At first, we thought this disease was thousand cankers, but Dr. Gary Moorman, professor of plant pathology at Penn State, says, “Butternuts are being eliminated from the east by another fungus, one that is probably (also) insect vectored.” In his trade magazine article and trade show seminar in Connecticut last November, Dr. Moorman said that English walnuts are susceptible to Thousand Cankers.

In the west, it takes eight to 10 years of continuous feeding by the beetle to kill a black walnut tree. We don’t know the impact in the east. The U.S. Forest Service has set up quarantines in all western states, and the three eastern states in which the disease has been found have set up quarantines. Several north central states in which black walnut trees grow have prohibited the importation of walnut, including black walnut, trees. New York is not one of them.

Thousand cankers disease is high on my list of insects and diseases to keep my eye on, but there is no evidence that it is anywhere near our area, unless someone recently transported black walnut logs here from the west. I certainly hope that is not the case.

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