Diseases team up on the butternut tree

A canker, a sign of butternut canker. Image: Manfred Mielke, USDA Forest Service, Bugwood.org

Last month, the department announced the arrival of thousand cankers disease, a disease new to the state that threatens our native walnut and butternut trees. Early predictions indicate thousand cankers disease will likely be devastating to our walnuts.

For the butternut tree, also known as white walnut, this is the second major blow in the last century. Another disease, butternut canker, has already decimated nearly 80 percent of butternut trees in the southeast. In North Carolina, butternut trees are found almost exclusively in the western part of the state.

First found in Wisconsin in the late 1960s, butternut canker is believed to have been affecting trees in the south for much longer. It is similar to thousand cankers disease in that it is a fungal disease that causes tree death as a result of multiple cankers girdling branches and trunks. However, unlike thousand cankers disease, butternut canker is not primarily spread by an insect. Rather, it is spread by rainsplash, wind and possibly insects and birds. Nuts may also become infected, killing the seedling upon germination.

When a tree becomes infected, sunken, elliptical cankers may be visible. Dieback and tree death do not occur until theses cankers spread and merge together, shutting down the transportation tissues of the tree.

As a result of the devastation of this disease, butternut trees have been listed as a “species at risk” for endangerment. But not all hope is lost. Many are optimistic that the key to disease management is the development of resistant varieties of the species. In nearly 20 states, trees both completely healthy and trees infected but surviving the disease have been found. By using these trees to develop a breeding program, a tree resistant to butternut canker may be possible in the future.

However, the new challenge is not only to develop these resistant trees, but to save them from thousand cankers disease as well. Between these two lethal diseases teaming up on butternut, it is difficult to know what to expect for the future of the species.

A healthy butternut tree. Image: Richard Webb, self-employed horticulturist, Bugwood.org

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