April 19, 2010

Emergency Quarantine Issued in Effort to Prevent Thousand Cankers

The Missouri Department of Agriculture has issued an emergency rule banning the transport of walnut products from nine Western states. The quarantine, issued by the Department of Agriculture's Plant Industries Division, became effective April 12 to protect the state's black walnut trees from the spread of thousand cankers disease. 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.

Missouri is the first state to ban the transport of walnut products from areas where a beetle, and newly described fungus, blamed for the thousand cankers disease has been found. Although the disease has not been seen in Missouri, the potential cost of infestation could top $850 million over 20 years.

"As the nation's leading black walnut producer, we have the most to lose from the spread of thousand cankers. It is critical that we prevent the introduction of this disease into Missouri," said Director of Agriculture Dr. Jon Hagler. "This quarantine draws a line around our state allowing us to stop thousand cankers at the border and helps keep the infectious plant disease out of Missouri."

Thousand cankers disease is carried by the walnut twig beetle, a tiny insect that bores into walnut trees. The beetle carries a fungus that can form thousands of cankers under the bark of the host tree, destroying its ability to transport water and nutrients. Early symptoms include leaf yellowing and wilting. Walnut trees affected by thousand cankers typically die within two to three years after symptoms are discovered.

Originally found in the Arizona walnut species, thousand cankers affects many types of walnut trees to varying degrees, but is lethal to black walnut. Missouri is home to more than 55 million black walnut trees - twice the number of any other state - and the nation's largest producer of black walnut nut meats is located in Missouri. A recent Department of Conservation study found that the annual economic impact from a thousand cankers infestation in Missouri could exceed $135 million, including $36 million in wood products, $35 million in nut production and the loss of $65 million in landscaping and street trees.   

"It seems incredible that such destruction could come from a tiny beetle, but that is the destructive nature of invasive pests," said Missouri State Entomologist Collin Wamsley, the chief insect specialist with the Department of Agriculture, who issued the emergency quarantine. "The walnut twig beetle is just the latest invasive pest to threaten Missouri forests and forest products producers. Whether we're talking about this disease, the gypsy moth or the emerald ash borer, we must prevent people from carrying destructive insects and diseases into Missouri."

Non-native invasive pests are often transported by vacationers who bring firewood with them while camping, or through commercial shipments of wood products. Missouri's nine-state external quarantine includes any firewood cut from hardwood tree species and walnut products, such as nursery stock, green lumber or any other walnut material living, dead, cut or fallen. Walnut logs, stumps, roots, branches and wood chips are included. Products exempt from the ban include nuts, nut meats, hulls and bark-free, kiln-dried lumber with squared sides. Finished products, such as furniture, instruments and gun stocks, are also allowed.

The walnut twig beetle has been found in eight Western states: Arizona, California, Colorado, Idaho, New Mexico, Oregon, Utah and Washington, as well as in northern Mexico. The quarantine issued by the Missouri Department of Agriculture applies to walnut products from those areas, as well as from Nevada.  

For more information on thousand cankers disease, log on to mda.mo.gov . If you notice a suspicious decline in black walnut trees or otherwise suspect an infestation of thousand cankers, contact the State Entomologist at (573) 751-5505.