Hotline: 816.833.TREE (8733)

Friday, Jan. 16th 2015

Thousand Cankers Disease of Walnut

Screen Shot 2015-01-16 at 10.07.22 AMBlack walnut is ecologically and economically important to Missouri, and thousand cankers disease (TCD) represents a serious threat to this resource. TCD occurs when the walnut twig beetle (WTB), Pityophthorus juglandis, attacks walnut trees, spreading the fungus Geosmithia morbida which causes small cankers in the phloem tissue under the tree bark, eventually causing tree decline and mortality.

TCD has not been detected in Missouri; however there is concern that undetected TCD infestations could be present, or that spread may occur from western states or Indiana, Maryland, North Carolina, Ohio, Pennsylvania, Tennessee and Virginia where G. morbida or TCD has been detected. Potential long- distance spread of TCD through movement of infected walnut materials enhances this threat. Existing survey technology is not very sensitive, and TCD is unlikely to be detected until several years after introduction. Detection of well- established infestations makes eradication efforts difficult. It is important to conduct detection surveys for TCD, as well as inform citizens about the disease and the risk of wood movement from areas with known infestations.

In 2014, both the Missouri Department of Conservation (MDC) and the Missouri Department of Agriculture (MDA) conducted surveys for TCD using USDA Forest Service and USDA Farm Bill funding respectively. MDC placed 76 WTB pheromone-baited Lindgren funnel traps at high-risk locations with declining walnut trees (urban areas,campgrounds, sawmills) in central and south central Missouri. MDA placed 103 WTB traps in the St Louis and southwest Missouri metro areas. Visual surveys were conducted by both agencies in high-risk areas to identify potentially infested trees. Branches were examined from suspect trees. When suspicious symptoms were observed under the bark, sample branch sections were triple-bagged, placed in a cooler with ice and transported to diagnostic facilities for evaluation and culturing as needed. Survey efforts are rotated to different areas each year; 58 counties were sur- veyed in 2014. Since 2010, 1158 locations have been surveyed visually and 434 WTB traps deployed. No evidence of WTB or TCD has been detected in Missouri. Common walnut problems detected during surveys included drought stress, site-related issues, and infestation by several other wood- boring insects (primarily roundheaded and flatheaded borer larvae and ambrosia beetles).

Outreach efforts were continued to raise public awareness about TCD. Messages included the potential impact of TCD, the threat posed by movement of infected walnut materials, and identification of suspect trees. Several state agencies and institutions including MDC and MDA as well as stakeholder groups were involved in outreach.

Efforts in 2014 included media interviews, presentations, trainings, and displays at a variety of public and green industry meetings. Several brochures and other materials were provided to citizens to raise awareness of TCD. A TCD awareness ad ran in Rural Missouri and Missouri Ruralist magazines. A targeted internet ad campaign placed TCD awareness ads on 1,278,856 Missouri computer screens based on user interest in conservation, the environment, gardening, outdoor activities, or woodworking. A TCD awareness poster targeted for woodworkers and campers was developed for Missouri welcome centers, campgrounds, and stores catering to woodworkers and chainsaw users. A “hands-on” workshop to evaluate declining walnut trees and branch damage at a state park campground provided additional training on what staff from the Department of Conservation, Department of Natural Re- sources, University of Missouri Extension, and USDA FS Mark Twain National Forest should look for when examining declining walnut trees, and how they can assist with outreach efforts.

University of Missouri Extension and the Missouri Invasive Forest Pest Council developed a new public TCD webpage with information on what symptoms to look for and how to report a suspect tree, thousandcankers.aspx. MDC also maintains a website for more information on TCD, cankers. Missourians are encouraged to report suspect trees via the online reporting form which can be found linked to the TCD websites. Photos of suspect trees can also be emailed to as a first step in determining what trees should be visited by trained personnel.

By: Missouri Forest Health Update  December 2014 Newsletter

Leave a Reply

You must be logged in to post a comment.

University of Missouri Extension Master Gardener Program