Thousand Cankers Disease
Thousand Cankers Disease
Not long ago, you may have heard about the recent detection of Thousand Cankers disease in Haywood County within the Great Smoky Mountains National Park. In an effort to keep this disease from spreading into neighboring North Carolina counties, restrictions have been set-up to quarantine a variety of wood products and plant materials.
Thousand Cankers or Geosmithia morbida is a fungal disease of walnut (Juglans spp.) trees that is vectored or spread from tree to tree by the walnut twig beetle Pityophthorus juglandis. Thousand Cankers disease is a newly recognized pest that has produced widespread death of walnuts in many western U.S. states east of the Mississippi. Currently, this disease is found in Arizona, California, Colorado, Idaho, Nevada, New Mexico, Oregon, Pennsylvania, Utah, Virginia, Washington, Tennessee and now Haywood County (fall of 2012) North Carolina.
Trees susceptible to Thousand Cankers disease include many western walnut species along with black walnut and butternut trees from North Carolina. Fortunately, this disease does not affect pecan and hickory species.
Tree infection begins when adult walnut twig beetles native to the southwestern U.S., bore into the bark of a black walnut tree to lay their eggs. During this beetle activity, the pathogen is simultaneously introduced causing small lesions or cankers to form just under the bark at the site of infection. As more beetles penetrate into the bark, additional small cankers appear eventually covering the branches and trunk of the walnut tree. As the disease spreads, the upper crown of the tree will look thin with individual branches dying out. Leaves will have a smaller appearance with possible wilting and or discolorations. After infection, the tree slowly losses it’s ability to transport and store nutrients. Once symptoms appear, the tree has already been infected for quite some time. Death follows in about 2 -3 years.
Black walnut is a highly valued resource for humans and wildlife in the forms of wood products, ornamental landscape trees and as a food source for humans, birds and other small mammals. With Thousand Cankers disease now in North Carolina and neighboring states, it seems quite formidable to contain future outbreaks where native black walnuts can be found. In saying this, the primary focus is to prevent further spread of this disease.
The North Carolina Department of Agriculture & Consumer Services has released the following list of regulated items that cannot be moved outside the quarantined county.
- Walnut plants and plant parts including firewood
- Logs, stumps, roots & branches
- Composted and uncomposted chips
Exceptions to the above restrictions include nuts, nut meats, hulls, processed lumber with square edges that is 100 percent bark free and kiln-dried, and finished wood products without bark, such as furniture, instruments and gun stocks.
Controls for Thousand Cankers disease have not yet been established. Future studies are required to better understand the biology of the walnut twig beetle and the canker-producing Geosmithia pathogen. Potential spray applications are likely to have minimal effectiveness thus rapid detection and removal of infected trees currently remains the primary means of managing Thousand Cankers disease.
For additional questions about plant quarantine and restrictions contact Phil Wilson, NCDA&CS Plant Pest Administrator, at 919-707-3730. For additional information about this disease and what you should know as a landowner, go to the N.C. Forest Service website http://ncforestservice.gov/forest_health/forest_health_thousandcankers.htm.