Black walnut trees threatened by Thousand Cankers Disease
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Black walnut is a valuable timber species that is highly prized for both its wood and its nuts. However, an invasive forest pest called Thousand Cankers Disease poses a high risk to Michigan’s walnut trees. A new project at MSU seeks to enlist residents in protecting our forest and shade trees. Goals of this effort include providing a network for tracking and reporting possible new invasive pests such as Thousand Cankers Disease early, before these exotic invaders pests get a solid foothold in Michigan.
Black Walnut (Juglans nigra L.) is a highly regarded timber species –in the United States and across much of the world. The tree is not only sought after as food its nutritious nut, but as detailed by Purdue University, “black walnut wood demands high market prices for many uses including furniture, veneer, cabinets, interior architectural woodwork, flooring, and gunstocks.”
The nut meat from black walnut is prized by many because the nuts are a good source of protein and low in fat and cholesterol. Black walnuts are a nice alternative to the English Walnuts most commonly sold in grocery stores.
Black walnut is native to Michigan but most is found in southern Michigan – around the Muskegon, Clare and Bay County lines. In the forest, native black walnuts are rarely found growing in plantations. More often, individual black walnut trees in wooded areas grow in mixed species stands with sugar or red maple, oaks, yellow poplar, elm and ash. According to estimates from the US Forest Service Forest Inventory and Analysis data (2012), more than 3,461,000 black walnut trees grow in Michigan.
Consequently, black walnut is an important component of many of our southern Michigan forests as well as an attractive landscape tree. Given the impacts of emerald ash borer and Dutch elm disease, black walnut may become even more important in sites formerly inhabited by ash and elm. The high value wood, nuts and the attractive appearance of black walnut trees make this a species worth protecting.
Unfortunately, a new threat called Thousand Cankers Disease has been confirmed in the western U.S. and more recently in a few states in the central or eastern U.S. Thousand Cankers Disease, known as TCD, is actually considered a disease complex because it involves an insect called the Walnut Twig Beetle (Pityophthorus juglandis) and the fungal disease Geosmithia morbida. These tiny beetles carry spores of the fungus on their bodies and when they bore under the bark, they introduce the fungus into the tree. The fungus causes small patches of tissue under the bark to die. Over time, more and more of these “cankers” form, disrupting the flow of nutrients and eventually killing the tree. Many people have likened TCD to “death by a thousand paper cuts.”
A new project at MSU entitled “Eyes on the Forest: Invasive Forest Pest Risk Assessment, Communication and Outreach,” seeks to get Michigan residents involved in protecting trees in forest and urban forests. This project will provide a network for tracking and reporting possible new invasive forest pests such as Thousand Cankers Disease early, before an exotic invader get a solid foothold in Michigan.
