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Black walnut trees afflicted with thousand cankers disease will begin dying from the top down.
Photo courtesy U.S. Forest Service



Originally published: 2013-01-07 10:56:49
Last modified: 2013-01-07 10:56:49

Disease threatens black walnut trees

by Anna Oakes

State forest officials announced last week that a disease responsible for widespread death of black walnut trees in western states has been detected in North Carolina.


Thousand cankers disease, a fungus spread by the walnut twig beetle, was discovered in the Great Smoky Mountains National Park in Haywood County. As a result, the N.C. Department of Agriculture and Consumer Services has placed Haywood County wood products under quarantine.


"This marks the first time the disease has been detected in the state, and by placing restrictions on a variety of plant material and wood products, we hope to keep the disease from spreading into other counties," Agriculture Commissioner Steve Troxler said in a statement Jan. 3. "Something as simple as moving firewood from an infected area to an uninfected county could increase the risk of spreading this disease."


The Geosmithia morbida fungus causes thousand cankers disease. In addition to the black walnut, other species of walnut such as Arizona walnut, English walnut and California walnut have also shown varying degrees of susceptibility to this fungus, according to NCDA&CS.


A N.C. Forest Service website on thousand cankers disease notes that butternuts are also susceptible to the disease. Watauga County is home to the state champion butternut tree, with a circumference of 264 inches. The tree is located on the farm of David Yates in Matney.


The following items fall under the quarantine restrictions: walnut plants and plant parts including firewood, lumber, logs, stumps, roots, branches and composted and uncomposted chips. Regulated items cannot be moved outside the county.


Exceptions to the quarantine restrictions include nuts; nut meats; hulls; processed lumber with square edges that is 100 percent bark free and kiln-dried; and finished wood products without bark, such as furniture, instruments and gun stocks.


Phil Wilson, a NCDA&CS plant pest administrator, said state officials are working with sawmills and other wood industry representatives to help them comply with the quarantine.


"As long as it goes through a heating process, that takes away the risk," Wilson said. "Our goal with that quarantine is to try to slow the spread."


Wilson noted that the disease has already been detected in Tennessee and Virginia.


"It's not surprising it made its way over," he said.


A tree affected by thousand cankers disease will experience the death of limbs from the top down. The disease will kill a tree in about three to five years, Wilson said.


The nuts of black walnut trees serve as food for birds, squirrels and other small mammals. But unlike other trees, black walnuts do not occur in large stands in the forest, Wilson said.


"You're not going to notice the death of those like you would the hemlocks," he added. Hemlocks are dying en masse due to infestation by the invasive hemlock woolly adelgid.


The N.C. Forest Service website says "it is too early to tell" if thousand cankers disease will cause black walnuts to go extinct.


For more information, call Wilson at (919) 707-3730 or visit http://ncforestservice.gov/forest_health/forest_health_thousandcankers.htm.