Walnut Worries

By Susan Littlefield

First it was chestnut blight and Dutch elm disease, then dogwood anthracnose, the Asian longhorned beetle and the emerald ash borer. It seems as if some new threat to our trees is always on the horizon. Now it's black walnuts that are at risk from thousand cankers disease (TCD).

This disease, also known as walnut decline, is similar to Dutch elm disease in that the fungus that causes infection is spread from tree to tree by the walnut twig beetle. (The Dutch elm fungus is spread by elm bark beetles.) Without both partners in crime, there would be no disease.

As you might expect from its name, thousand cankers disease kills trees as multiple cankers form and coalesce, girdling and killing limbs and eventually the entire tree. The first signs are yellowing of leaves and thinning in the top of the crown of the tree. An infected black walnut will usually succumb within three years of the first symptoms.

TCD was first identified in Colorado in 2003 and has caused widespread death of black walnuts in western parts of the country. Then last summer it was found in Tennessee and is now considered a threat to eastern trees. A number of midwestern and southeastern states have instituted quarantines to try to prevent the spread of TCD.

No cures for this disease have yet been identified; detection and removal of infected trees remains the best control at this point. One way individuals can help limit its spread is to refrain from moving firewood, especially from areas where TCD has been found.

For more information on thousand cankers disease, including a symptom checklist, go to: Tennessee Dept. of Agriculture- Thousand Canker Disease.

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