Birch Borer
Bronze birch borer is a serious problem in the Twin Cities area.
These insects attack stressed birch trees and feed on the inner bark. The
vascular system of the tree, which carries water and nutrients, is eventually
destroyed. Signs of borer infestation include leaves at the top of the tree
and tips of the branches turning brown, then the branch dies. Raised areas
appear under the bark resembling varicose veins. This is the tunnel that
the larva creates as it feeds. Eventually the entire tree is killed.
The best method of control is prevention. Adult borers primarily attack stressed and weakened trees. They lay eggs in the bark or around wounds. Birch will thrive in cool, moist, and shaded planting sites. They are not well adapted to open, exposed, sunny locations. In fact, adult borers prefer trees that are in full sun. The river or red birch has shown more resistance to borer attack than other types of birches.
Birch tree vigor can be maintained by providing weekly, one-to-two inches of water over the entire root zone, if rainfall has been inadequate. Mulching under the canopy of the tree will help hold soil moisture and keep the root system cool.
In August, prune branches showing symptoms of attack. This will prolong the useful life of the tree. However, if the main trunk is showing signs of attack, it is time to consider planting a tree more suited to the site.
Revised: 03/10/98
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