Thousand cankers disease complex: a forest health issue across the U.S.

Authors: DANIELS, DIXIE - Oregon State University; LORD, ROBERT - University Of Tennessee; NIX, KATHERYNE - University Of Tennessee; Wadl, Phillip; VITO, LISA - University Of Tennessee; WIGGINS, GREGORY, J - University Of Tennessee; WINDHAM, MARK - University Of Tennessee; OWNLEY, BONNIE - University Of Tennessee; LAMBDIN, PARRIS - University Of Tennessee; GRANT, JEROME - University Of Tennessee; MERTON, PAUL - Us Forest Service (FS); HADZIABDIC, DENITA - University Of Tennessee

Submitted to: Forests
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2016
Publication Date: 11/3/2016
Citation: Daniels, D.A., Lord, R.J., Nix, K.A., Wadl, P.A., Vito, L.M., Wiggins, Gregory, J., Windham, M.T., Ownley, B.H., Lambdin, P.L., Grant, J.F., Merton, P., Hadziabdic, D. 2016. Thousand cankers disease complex: a forest health issue across the U.S.. Forests. 7:260. doi:10.3390/f71102260.

Interpretive Summary: Black walnut trees are dying throughout their native range in the eastern and midwestern United States because of a fungal disease called thousand cankers disease (TCD). The disease is spread by the walnut twig beetle which has expanded its range. Discovery of TCD within the native range of black walnut occurred in 2010 and has spread to six states in the eastern U.S. Disease symptoms are similar to effects of drought which make diagnosis difficult without molecular confirmation. Black walnut is valued around $568 billion and is a vital component of the eastern deciduous forest ecosystem. Techniques to mitigate TCD begin with quarantine efforts to prevent movement of diseased logs and then move to chemical control if quarantine efforts fail. Research and field training are both vital to continued protection of black walnut. Continued research focusing on field identification and confirmation of TCD is needed, especially in eastern states where cankers may be small or absent. Research into more advanced molecular detection methods can aid difficult field identification situations. At the same time, increased industrial and governmental oversights are needed to enforce existing legislation regarding movement and sale of walnut logs. Multiple avenues of advancement in our understanding of TCD and its spread will help save black walnut.

Technical Abstract: Thousand Cankers Disease (TCD) is a disease complex wherein the fungus (Geosmithia morbida), is vectored by the walnut twig beetle (WTB, Pityophthorus juglandis). Disease causes mortality primarily of eastern black walnut (Juglans nigra), though other walnut species are also susceptible. Eastern black walnut is native to the Eastern and Midwestern U.S. but is widely planted in western states. Tree standing volume in both urban and forested settings is approximately 96 million cubic meters, and is valued at $539 billion. Although native to the Southwestern U.S., the range of WTB has expanded considerably. The spread of G. morbida coincides with the spread of WTB. TCD was introduced into Tennessee in 2010, and has spread to seven eastern states. Trees infected with TCD exhibit drought-like symptoms, making field detection difficult without molecular and/or morphological methods. The recently sequenced G. morbida genome will provide valuable research tools focused on understanding gene interactions between organisms involved in TCD and underlying mechanisms of pathogenicity. With no chemical treatments available, quarantine and sanitation are currently the only options for slowing the spread of TCD, although biological control agents have been discovered. High levels of eastern black walnut mortality due to TCD will have far-reaching implications for both eastern and western states.