In an attempt to halt the devastating spread of thousand cankers disease, which afflicts black walnut trees, the state of Missouri has issued an emergency quarantine banning the importation of “walnut products” from nine Western states. According to Missouri officials, “The ban applies to nursery stock, unprocessed lumber, logs, wood chips, mulch and other products created from walnut trees, as well as any hardwood firewood originating from or traveling through affected states.”

The quarantined states are Arizona, California, Colorado, Idaho, New Mexico, Nevada, Oregon, Utah and Washington. Thousand cankers disease has been detected in all of these states except Nevada, which is surrounded by affected states. The disease is caused by a fungus in the Geosmithia genus, which is carried around by the walnut twig beetle (Pityophthorus juglandis). The beetle was just another bug until it joined up with the fungus, but together, they are wreaking devastation on black walnut forests in California and elsewhere.

The disease has not been detected in Missouri, and officials want to keep it that way. The state is home to some 55 million black walnut trees – far more than any other state. It’s estimated that an infestation could cause $850 million in economic damage over 20 years. (Photo by Kathy Keatley Garvey, University of California at Davis.)