Thousand Cankers Disease

thousand cankers as seen in black walnut trees

Thousand cankers disease (TCD) is a new disease of the Walnut genus that is especially damage-causing in the Black Walnut (Juglans nigra) species.

Deadly to Black Walnut

Relatively harmless to Walnut species within the Walnut Twig Beetle’s native range, TCD is devastating to eastern members of the Juglans genus such as Black Walnut. TCD has not yet been discovered in Ohio, but the Walnut Twig Beetle has, and great efforts are currently underway to prevent TCD from infecting and destroying our Black Walnut trees.

Although mortality of infected trees is ultimately caused by the Geosmithia morbida fungus, this fungus is transported to host trees by the Walnut Twig Beetle (WTB). The fungus is introduced to a given tree by normal aspects of the Walnut Twig Beetle’s lifecycle—burrowing into and overwintering within the bark and layers of the host tree.

Once the adult beetle has emerged, spores deposited within the tree grow rapidly around the exit wound on the side of the infected tree. Cankers are initiated each time a beetle bores into the tree and over time a small number of cankers turns into many and ultimately disrupts the cambium of the tree. Though it is not clear how the disease began, what is clear is that this disease is detrimental to eastern Black Walnut populations and threaten a valuable economic and ecological resource.

The Walnut Twig Beetle is native to Mexico and parts of Arizona, New Mexico and California. While western species of the Walnut genus such as Arizona Walnut and Northern California Walnut are highly resistant or even immune to the disease, Black Walnut, which is pervasive throughout the eastern hardwood forest, has a high degree of mortality when confronted with TCD. This susceptibility was first observed in Black Walnut groves located in California.

Timber Quarantines Loom

…for a second year in a row the Walnut Twig Beetle has been found in Butler County, Ohio and for the first time ever in our state a quarantine on Walnut trees located within Butler County has been implemented.
Unlike the Emerald Ash Borer currently affecting Ohio’s Ash population, TCD is hard to recognize and shows few visible signs within infected trees early on in the disease-cycle.

In fact, by the time symptoms are noticeable, tree death can occur in as little as three years. The first visible sign of TCD is a yellowing of the upper canopy which can occur in very few or even single branches. Sudden leaf wilting characterizes the end stages of TCD appearing in large branches or the entire canopy at once.

Living up to its name, the disease is slow and methodical in the manner with which it ultimately kills a host Walnut tree. Small cankers form at the site of each beetle attack. Over time, the number of cankers on a tree grows as more and more Walnut Twig Beetles bore into its bark and cambium.

Eventually, the fungus envelops the tree and the thousands of cankers on its surface coalesce, cutting off the flow of water and nutrients throughout the tree.

TCD has not yet been discovered in Ohio Walnut populations, but the disease has been found in three eastern states—Tennessee, Pennsylvania and Virginia. However, for a second year in a row the Walnut Twig Beetle has been found in Butler County, Ohio and for the first time ever in our state a quarantine on Walnut trees located within Butler County has been implemented.

Timber Owners Be Watchful

For now, we watch the development of this disease with cautious optimism that quarantines will be effective against the spread of the disease. The Black Walnut population throughout our region’s hardwood forest would be a terrible thing to lose—in addition to providing valuable nutrients to native wildlife populations, these trees produce beautiful, classically-enduring lumber used in furniture, flooring and cabinets.

The USDA estimates the value of the Black Walnut stand located in the eastern United States at 500 billion dollars. Losing such a valuable resource would be a terrible turn for our forests.

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