Whitney Cranshaw, Colorado State University; bugwood.orgCankers under the bark of a walnut tree caused by thousand cankers diseaseThousand cankers disease, a fungal malady spread by the walnut twig beetle, is on the march.
During the past decade, the disease has killed numerous native and commercial walnut trees in the West.
Since 2010, it also has been found in several locations east of the Rockies, including Tennessee, Virginia and the outskirts of Washington, D.C., according to a news release.
The disease has not been found in Missouri yet, but is on the watch list for Extension forestry specialist Hank Stelzer and walnut breeder Mark Coggeshall.
The disease attacks many species of black walnuts as well as the cultivated English walnut.
The beetle, which carries fungal sports, burrows into the tree during feeding.
The fungus—Geosmithia morbida—destroys small patches of tissue and creates cankers under the bark.
The cankers grow and merge, causing branches to die and eventually killing the tree.
In the process, it transmits the disease, which plugs the phloem and eventually kills the tree.
Early symptoms include yellow leaves and thinning foliage in the upper crown of the tree.
Larger limbs die as the disease progresses.
Trees typically die within three years of when the infection is first seen.
The disease is harmless to humans and animals.
Several states, including Missouri, have imposed quarantines that ban the transportation of firewood to try to stem disease spread.
One concern is the Internet sales of walnut planks with the bark still intact, which can be infected.
For more information, visit www.thousandcankers.com.