Spruce beetle a native bark beetle seldom seen in Minnesota has been killing large diameter white spruce trees along the shore of Lake Superior the past few years. The amount of mortality is increasing and expanding as new infestations continue to be found. The problem was first noticed in Judge Magney State Park in Cook County. Dying trees have now been found along Lake Superior as far south as Gooseberry Falls State Park. Spruce beetle caused mortality is most obvious within a few miles of Lake Superior but has also been found in a number of white spruce stands in Koochiching County as well in a dying spruce windbreak in Wadena County. Spruce beetles ares likely present in new locations and will be found as more people learn to look for and identify them.
The beetles prefer large diameter trees (12 inch diameter and larger) but have been found in trees as small as six inches in diameter. They also prefer stressed trees but have also been killing some pretty healthy looking ones. A large tree can be killed in one growing season if attacked by a large number of beetles. Recent attacks on trees are best found by looking for pitch tubes on the trunks of the trees.
Don't know what pitch tubes look like? Just look in your past issues of the Forest Insect and Disease Newsletter which you probably have bound and displayed in a prominent location in your home. You certainly wouldn't be throwing them away would you? The April 27, 2001 issue of this newsletter has pictures of the spruce beetle and pitch tubes. You can also find advice on spruce beetle management in those valuable back issues of the newsletter, namely the August 7, 2002 issue.