Thousand Canker Disease (TCD) of Black Walnut Found in Knoxville, TN
Thousand canker disease (TCD) of black walnut was recently identified in the Knoxville, TN area. This find is significant because the disease had not been detected east of the Mississippi River and was originally thought to be limited to Colorado and a few other western states. It is believed that due to the severity of the disease in Tennessee that it has probably gone undetected in the trees for years. Foresters believed the declining walnut trees were dying due to drought stress. These same conditions exist throughout Georgia and many tree species are showing symptoms of stress....
TCD is caused by a fungus, Geosmithia sp., that is introduced into the tree by a twig beetle. Infected trees die from multiple cankers that infect the cambial tissues of the black walnut trunk and branches. The trees are not killed from girdling cankers, but from a collective group of shallow cankers that interfere with water and nutrient transport, similar to how Seiridium canker affects and kills Leyland cypress trees. There is no control other than removal of infected trees and wood to reduce disease and beetle spread. Beetles can reproduce within cut logs and it is believed that transport of infested wood (logs with bark still attached) can spread the beetle and disease to new areas. The best control is for this disease is early detection.
TCD has not been identified in Georgia. However, if you receive calls from arborists, foresters or homeowners with declining black walnuts, you might want to get a sample to determine if TCD is the cause of the flagging and crown decline. Once symptoms of crown decline are evident, which can be several years after infestation by the beetle, infected trees die within 2-3 years. Below is a link from the Tennessee Department of Agriculture containing information about the disease, as well as a symptom checklist to help identify potentially infected trees. I also included a link showing the known distribution of native black walnut stands within Georgia; however, this information does not include distribution of black walnut planted in landscapes or other settings.
http://tn.gov/agriculture/regulatory/tcd.html
http://plants.usda.gov/java/county?state_name=Georgia&statefips=13&symbol=JUNI
If you have any questions, please contact me (706-542-9140 office; 706-540-7738 cell; jwoodwar@uga.edu)
