October - December 2013
Thousand Cankers Disease of Black Walnut
Black 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 Geosmithia morbida fungus that 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 North Carolina, Ohio, Pennsylvania, Tennessee and Virginia where it 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 2013, both the Missouri Department of Conservation (MDC) and the Missouri Department of Agriculture (MDA) conducted surveys for TCD using USDA Forest Service and federal Farm Bill funding respectively (see map). MDC placed 50 WTB pheromone-baited Lindgren funnel traps at high-risk locations with declining walnut trees (urban areas, campgrounds, sawmills) in central and southeast Missouri. MDA placed 143 WTB traps in the St Louis, Kansas City and southwest Missouri metro areas. Visual surveys were con-ducted 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. Since 2010, 850 locations have been surveyed visually and 255 WTB traps deployed (see map on page 4). No evidence of WTB or TCD has been detected in Missouri. Common walnut problems detect-ed during surveys included drought stress, site-related issues, and infestation by several other wood-boring insects (primarily round-headed and flatheaded borer larvae).
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 2013 included TV and radio interviews, presentations, trainings, and displays at a variety of public and green industry meetings. An updated TCD FAQ for Missouri, TCD identification card, and brochure for homeowners are available from MDC to raise awareness. MDC also maintains a website for more information on TCD, www.mdc.mo.gov/thousand-cankers. Missourians are encouraged to report suspect trees via the online reporting form which can be found linked to the TCD website or here on the University of Missouri Extension website. Photos of suspect trees can also be emailed to forest.health@mdc.mo.gov as a first step in determining what trees should be visited by trained personnel.
An action plan has been drafted to organize the Missouri response to the threat of TCD. The plan describes several efforts to slow the spread of TCD and prepare for a potential detection including continued outreach activities and monitoring of trees at high risk sites. It also describes a response to detection of an infestation and includes a list of key stake-holders to keep informed. This action plan will supplement the Missouri Invasive Forest Pest Plan currently under development.