ST. PAUL  (AP) -- Minnesota is taking steps to protect its eastern black walnut trees from a tree-killing disease.

State Agriculture Commissioner Dave Frederickson has restricted the import of walnut trees and wood into Minnesota from areas known to be infested with Thousand Cankers Disease.

The disease is caused by a fungus carried by a tree pest called the walnut twig beetle. The beetle introduces the fungus while tunneling under the walnut tree's bark. That results in small cankers, or dead areas, under the bark. The cankers grow together and cut off the tree's circulation, killing the tree.

The disease has been found in Arizona, California, Colorado, Idaho, New Mexico, Oregon, Tennessee, Washington and Utah.

Minnesota has 6 million eastern black walnut trees. Black walnut is used in products such as furniture and musical instruments.

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