Emergency Exterior Quarantine Issued for Black Walnut

Published: May 1, 2010

As of April 12, 2010, an emergency rule was issued by the Missouri Department of Agriculture to prevent the spread of thousand canker disease into the state. All walnut nursery stock, bark, budwood, scionwood, green lumber, fire wood, and other living or dead plant material from Arizona, California, Colorado, Idaho, Nevada, New Mexico, Oregon Washington, Utah or any other areas of the United States that have thousand cankers disease is prohibited into Missouri, as well as transiting through the state. This also includes logs, stumps, roots, branches and composted and uncomposted chips. Exceptions to this quarantine include nuts, kernels, hulls, processed lumber (100% bark-free, kiln-dried with squared edges), and finished wood products without bark, including walnut furniture, instruments, and gun stock. Any plant material or articles transported into Missouri in violation of the quarantine may be destroyed or returned to the point of origin at the discretion of the state entomologist and penalties will be imposed upon the carriers of the regulated material as stated in the Missouri Plant Law.

Thousand canker disease is an insect-fungal complex that is lethal to walnut trees, occurring in western states. The walnut twig beetle (Pityophthorus juglandis) and the fungus, Geosmithia morbida sp. nov. are associated with the disease. This insect is a small (1.5-1.9 mm) yellowish-brown bark beetle. Adults overwinter in cavities excavated in the bark of the tree trunk. In the spring, mating occurs and new tunnels are formed for egg galleries. During tunneling, the Geosmithia fungus is introduced with the insect and subsequently spreads. Cankers with dark staining then develop around the tunnels of the twig beetle. Cankers form on the bark surface the tree but they may not be always be visible until the outer bark is removed to expose the tunnels around the galleries. The first symptoms of thousand cankers disease are leaf yellowing and branch dieback in the upper part of the tree. Limb mortality occurs and eventually, the whole tree dies. More information regarding thousand cankers disease can be found at http://mda.mo.gov/plants/pests/thousandcankers.php.

While thousand cankers disease has not yet been found in Missouri, the Department of Conservation has estimated that its introduction could cause annual losses of more than $36 million in wood products, $35 million in nut production, and $65 million in urban street trees. Over a 20 year period, this disease could cause over $851 million losses in Missouri. The current emergency quarantine will expire on January 11, 2011, although the development of a longer term ruling is underway. For more information regarding the quarantine, contact Collin Wamsley, State Entomologist, Plant Pest Control Bureau, MO Department of Agriculture at 573-751-5505 Collin.Wamsley@mda.mo.gov.