Thousand cankers disease (TCD) results from the combined activity of two organisms; a newly described fungus, Geosmithia morbida, and the walnut twig beetle (WTB), Pityophthorus juglandis. Trees are eventually killed by overwhelming attacks of the walnut twig beetle and subsequent cankers that girdle branches.
WTB are tiny yellowish-brown bark beetles, about the size of a small flea or a broken piece of lead from a mechanical pencil. See image gallery below.
Thousand cankers disease is a newly recognized insect/disease complex that currently threatens millions of black walnut trees in forests and urban areas, an important species with great economic and ecological value throughout its native range in the eastern half of the US. TCD was recognized in 2008 after specimens of a tiny North American beetle, in association with a new fungus, were consistently isolated from cankers of declining walnut trees. In the last decade, TCD has produced widespread death of walnuts in many western states. These trees are outside of the native range of black walnut. In 2010, TCD was confirmed within the native range of black walnut in Knoxville, Tennessee. Since then, surveys have been ongoing in eastern states, and confirmed cases of TCD are beginning to be reported. Researchers still do not know what impact TCD will have within native eastern black walnut ecosystems. However, should it become established, a multi-million dollar walnut industry is at stake.
TCD spreads naturally when beetles carrying the fungus colonize new unaffected trees; however, the principle pathway for spreading TCD is the movement of infested wood material including logs, firewood, non-dried lumber for woodworking. WTB reproduces in TCD infected trees and logs with the bark intact. Moving walnut material is risky because it can take years for trees to become symptomatic. Learn more about human-assisted spread of plant pests and pathogens from our friends at Don't Move Firewood.
- Primarily black walnut, Juglans nigra
- Butternut, J. cinerea
- Research is ongoing for other Juglans spp.
A black walnut tree can be infected with TCD for many years before one observes symptoms, but once symptoms become apparent, trees usually die in a couple seasons.
In the occurrance of infection, these symptoms will begin at the top of the plant and appearing in sections:
- Flagging, yellowing foliage, wilting
- Dead branches
- Tiny holes on dead and dying branches
- Epicormic shoots
If you suspect an occurance of TCD, do NOT transport dead or dying walnut wood, branches or twigs offsite, but DO investigate walnuts thoroughly and report suspected cases. Instructions may be found below.
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