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Photo courtesy of Kathy Keatley Garvey, UC Davis Department of Entomology
The American ash tree is under attack from the emerald ash borer, the American chestnut has been all but wiped out by chestnut blight and the American elm is succumbing in large numbers to Dutch elm disease. Now, the Eastern black walnut (Juglans nigra) is under attack from “Thousand Cankers Disease.”
This fungus (an undescribed exotic species of Geosmithia) hitchhikes on a tiny bark beetle called the walnut twig beetle (Pityophthorus juglandis), which by itself does relatively little damage, according to experts quoted in a number of online articles. But the virulent fungus that it carries can kill a specimen in as little as three years.
The tiny beetle (it’s smaller than a grain of rice) bores into living walnut trees and creates tunnels beneath the bark, thus wounding the tree and providing an opportunity for the fungus to invade. The aggressive fungus quickly spreads in large cankers that girdle twigs and limbs, causing the tree’s crown to die back
For now, Thousand Cankers seems limited to seven western states: Oregon, Idaho, Utah, Colorado, Arizona, New Mexico and pockets of California. (The walnut twig beetle is native to Arizona, California, New Mexico and Mexico.) While entomologists are researching methods to combat the disease, right now the only defense is to limit the geographic area and keep it from spreading. That means no transportation of walnut from the infested site. Cut logs can, according to a press release from Linda McMulkin at Colorado State University, harbor the fungus and the beetle for up to three years. McMulkin urges those with infested trees to cut down the diseased trees and keep the wood on the property.
I have queries in to several experts right now to find out the ramifications for woodworkers. I’m interested in knowing , as I’m sure are you , if this affected wood can be used. Here are the questions I want answered:
– Once the beetles have tunneled into it and the canker sets in, does the wood maintain enough structural integrity to be used? (If so, I can see it being used as a dark alternative to wormy and/or spalted maple.
– If air-dried, the pathogens presumably would remain viable in the walnut for up to three years , so is milling the wood a health threat to the woodworkers?
– If it can be safely worked, might a finish kill or sufficiently contain the beetle and fungus, thereby rendering safe the transport of a finished project?
– Can the affected wood can be safely kiln dried, and does that process kill off the pathogens and lessen any health threats from airborne fungus released in the milling process?
If you have other questions, please post a comment; I hope to soon get answers (and if you’re a plant pathologist/biologist/entomologist/cross-taxonomic fungi expert, please give me call!).
