Plant Industry - Plant Protection Section
Entomological and Plant Disease Services
Thousand Cankers Disease of Black Walnut
Thousand Cankers Disease threatens eastern black walnut (Juglans nigra), a high value, ecologically critical, and culturally treasured tree species in North Carolina. The disease is caused by a fungus, Geosmithia morbida, spread by the walnut twig beetle (Pityophtorus juglandis Blackman (Coleoptera: Scolytidae)) and can kill trees in as few as three years once symptoms appear. Thousand cankers disease may also infect butternut trees (Juglans cinerea).
Symptoms – Symptoms of thousand cankers disease include yellowing and wilting of leaves and limb dieback. Numerous tiny cankers may be present on tree branches and boles.
|Yellowing and wilting leaves||Crown thinning and dieback||Branch cankers|
|Ned Tisserat, CSU, Bugwood.org||Curtis Utley, CSUE, Bugwood.org||Ned Tisserat, CSU, Bugwood.org|
Disease distribution - East of the Mississippi River, the disease is known to occur in North Carolina, Tennessee, Virginia, Maryland, Pennsylvania, Ohio, and Indiana. The disease and beetle are widely distributed in the western United States.
In North Carolina, thousand cankers disease is known to occur in Haywood County.
How it spreads – The fungus, Geosmithia morbida is transmitted by the walnut twig beetle, Pityophthorus juglandis. This tiny beetle (approximately 1.5 mm) introduces the fungus to walnuts as it bores into the inner bark. The fungus causes small cankers. However, with enough beetle activity over time, numerous cankers eventually coalesce and kill the tree, thus the name “thousand cankers.”
Walnut Twig Beetle (Pityophthorus juglandis )
Steven Valley, Oregon Dept. of Agriculture, Bugwood.org
The human-assisted spread of the beetle is primarily through the movement of firewood, logs, lumber, and untreated wood products used for crafts or other purposes.
What you can do - To report potential new occurrences of the walnut twig beetle and/or thousand cankers disease do the following:
- Call NCDA&CS at 1-800-206-9333 or email email@example.com
- Contact your NC Forest Service county ranger
- Do not collect and send samples as this may spread the pest further. Samples will be collected by NC Forest Service or NCDA&CS Plant Industry Division personnel.
You can also help reduce the spread of the disease by buying/cutting firewood close to where you intend to burn it and by not moving un-barked and untreated wood for woodworking or other purposes.
Regulatory Efforts - NCDA&CS Plant Protection personnel use traps baited with pheromone to survey for walnut twig beetle throughout the state. It is critical that we understand where the beetle and disease occur in order to enforce quarantines successfully.
Quarantine - The occurrence of thousand cankers disease was first reported in NC in Haywood County, along the North Carolina/Tennessee border in 2012. Haywood County is now under quarantine for thousand cankers disease. As a result, the movement of all regulated commodities outside this quarantined area are subject to state regulations. The following items fall under the quarantine restrictions: walnut plants and plant parts including firewood, lumber, logs, stumps, roots, branches, and composted and un-composted chips. Regulated items cannot be moved outside the county. Exceptions to the quarantine 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.