Thousand cankers disease

Thousand cankers disease (TCD) is a disease complex native to the western United States and primarily affects black walnut, Juglans nigra. This disease is the result of the combined activity of a fungus, Geosmithia morbida, and the walnut twig beetle (Pityophthorus juglandis). The disease was first identified in 2008.

Symptoms and Signs

The initial symptoms of TCD are yellowing and thinning of the upper crown, followed by wilting and death of branches. The symptoms are similar to drought stress, so the disease may not be immediately recognized. The cankers, or dead areas under the bark caused by the fungus, are not visible until the bark is peeled back.

Disease Cycle

The walnut twig beetle carries spores of the fungus and introduces them into the tree when it bores into the bark. The fungus then grows in the phloem tissue of the tree, causing cankers. The beetles reproduce within the tree, and new generations of beetles emerge from the tree carrying fresh spores of the fungus.

Management

There is currently no cure for TCD. Management strategies include maintaining tree health and promptly removing and destroying infested trees to prevent the spread of the disease.

See Also

• Walnut twig beetle
• Geosmithia morbida
• Juglans nigra

References

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