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Virginia's walnut trees face threat from approaching fungus Date published: 9/4/2010
BY DONNIE JOHNSTON During the midst of a campaign to protect Virginia's ash trees from an invasive insect, an approaching fungus now may pose a formidable threat to the state's black walnut trees. In July, thousand cankers disease, which originated in America's western states, was detected in Knox County, Tenn. (outside of Knoxville), which is only about 100 air miles from Virginia's westernmost tip. This discovery is significant because it is the first occurrence of the disease east of the Mississippi River. "The presence of this devastating disease in the eastern part of Tennessee poses a great risk to black walnut trees in Virginia," states a Virginia Tech advisory issued to all state agriculture agents last week. The worst thing about the disease is that it may be present long before anyone knows it is there. "It could be in the tree several years before you see the symptoms," said Larry Nichols, program manager for Virginia's Office of Plant Industry Services. The progressive disease is caused by a fungus called geosmithia that is carried by the walnut twig beetle. This insect burrows into the bark, infecting the tree with the virus. The virus multiplies and forms numerous cankers, or sores, on the walnut tree's bark, ultimately killing individual branches or the entire tree. The origin of the disease remains unclear, but scientists believe it may have jumped from naturally resistant species of western walnut trees to non-native black walnut trees in Utah, New Mexico and Colorado in the late 1990s. "This is very new," Nichols said. Nichols said he could not predict how long it would take the disease to spread to Virginia. But the threat is serious because the black walnut tree has been spreading extensively across the state over the past two decades. Walnut wood is prized by furniture makers, and there has been a resurgence of interest in harvesting the nuts for cooking or eating because of their health benefits. "The walnut is a very valuable tree," Nichols said. A few weeks before thousand cankers disease was discovered in Tennessee, three more occurrences of emerald ash borer infestations were discovered in Frederick County, Va. (north of Winchester and near the West Virginia state line), Nichols said. This insect, which infects and can kill ash trees, was first discovered in Fairfax County in 2003. For the past two years, the Virginia Department of Agriculture has hung more than 3,000 purple traps from ash trees around Northern Virginia to determine wheth-er the emerald ash borer has spread from Fairfax County. Nichols said his department believes the insects may have been brought to the Frederick County area in firewood. There is a West Virginia park with camping just a few miles away. A quarantine on firewood is now in place in Frederick, Clarke, Prince William and Fairfax counties. Donnie Johnston:
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