The Thousand Cankers Disease (TCD) of walnuts, particularly black walnuts, that was previously thought to occur only in the western U.S., was recently found near Knoxville, Tennessee. Based on the relatively widespread distribution of the disease in the surrounding area and the fact that many of the affected trees were in advanced stages of decline, it is thought that TCD, caused by the fungus Geosmithia morbida, and it’s vector, the walnut twig borer (Pityophthorous juglandis), more than likely have been in the area for at least 20 years. Symptoms of TCD include dieback of the crown and flagging of individual branches (i.e., yellowing of leaves still attached to the branch or browning of leaves that have collapsed and wilted). Another diagnostic feature associated with dead or dying branches is the occurrence of tiny exit holes. When the bark around the exit holes is peeled back, larval galleries are usually evident. Although the disease poses a major threat to walnuts throughout the eastern U.S., it will probably not be a major problem in Louisiana as we do not have a substantial number of walnut trees in the state.
Photos by Whitney Cranshaw and Ned Tisserat, Colorado State University; used by permission of Bugwood.org.