In an effort to protect the estimated six million Black Walnut trees in Minnesota, the Minnesota Department of Agriculture has implemented an exterior quarantine of walnut wood from entering the state. The Minnesota Department of Agriculture wants to stop Thousand Cankers Disease from infecting Black Walnuts in Minnesota. Thousand Cankers Disease, first discovered in the western United States, is fatal to Black Walnut trees.
The quarantine stops products such as live walnut trees, mulch made with walnut wood, and walnut logs from being imported into Minnesota. The quarantine does not include finished walnut wood products, kiln-dried walnut lumber or walnut nuts.
Thousand Cankers Disease fungus spores are carried from tree to tree by the tiny Walnut Twig Beetle. The disease causes a small canker to be formed under the bark of the walnut tree. As more Walnut Twig Beetles attack a tree more and more cankers are formed. Eventually the cankers coalesce together and inhibit the natural movement of water and nutrients in the cambium of the tree. Black Walnut trees are usually killed within 2 – 3 years from when dieback is noticed at the top of the tree. There are no fungicide treatments available to protect Black Walnut trees from Thousand Cankers Disease.
Early detection is critical to limiting the spread of Thousand Cankers Disease, if it should make its way to Minnesota. The disease affects the top of a Black Walnut first by causing a thinning of the foliage and killing small tree branches. The disease gradually affects larger and larger branches until eventually the whole tree is dead. Homeowners should contact an arborist or the Minnesota Department of Agriculture if they suspect Thousand Cankers Disease has infected their Black Walnut tree.
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