As if the specter of emerald ash borer and Asian longhorned beetles destroying hardwoods in the Northeast weren’t depressing enough, another forest pest has reared its ugly head in the Midwest.
Just two years ago, researchers discovered that a sudden decline in black walnut (Juglans nigra) in Colorado was due to a combination of the walnut twig beetle and a previously unknown fungus. In July, 2010, the disease was identified in Tennessee – right in the center of black walnut’s native range. With a mortality rate near 100 percent, it’s frightening to think of what would happen if the disease expands throughout the country.
According to Whitney Cranshaw, professor of bioagriculture science and pest management at the University of Colorado, if the disease becomes established east of the Mississippi, it could develop into an uncontrollable outbreak. “This may ultimately have the potential to destroy black walnut in its native range,” said Cranshaw.
Harlan Palm, president of the Missouri Walnut Council, estimates that the loss of walnut trees in Missouri alone would amount to roughly a half billion dollars. Serious tree farmers throughout the region have been tending walnut plantations for decades to provide retirement income or to leave something of value for their grandchildren. What a blow this would be for them.
The disease is similar to Dutch elm disease in that the lethal agent is a fungus that is spread by a beetle. Although smaller than a grain of rice, the beetles are devastating in their sheer numbers. Researchers have found as many as 20,000 beetles in a four-foot section of a small walnut log. The fungus they bring with them destroys the tree’s cambium layer, which causes the tree to starve to death. Cankers form on the dead cambium, which gives the disease its common name: walnut thousand canker disease. This new fungus is so deadly that in Latin it’s been dubbed Geosmithia morbida.
Black walnuts are only native in pockets throughout New England, though many ornamental trees in urban areas could be affected. Black walnut is more substantially represented as a forest tree in parts of New York and Pennsylvania. In the Appalachian forest, many livelihoods depend on walnut trees, and woodworkers, loggers, log buyers, sawmillers, the edible nut industry, furniture makers, carvers, and the makers of many specialty walnut products are all watching closely to see what happens next.
There are some steps that should be taken in all parts of North America to help avoid the spread of this disease. Do not move walnut logs, slabs, or firewood from infested areas. A single log with live beetles can be the source of an outbreak. Kiln-dried lumber is safe. Woodworkers, lumber yards, tree removal services, and firewood distributors are among the groups that need to be provided information on this new disease. You can also help by letting others know about it. An excellent source of information on the Internet is www.thousandcankerdisease.com.
Help spread the word, not the disease!
