Bronze birch borer is a common pest of paper birch varieties. The pest is classified as a flat headed borer. This insect is similar to the emerald ash borer in many ways, such as the larvae damage the tree by eating the cambium layer of the tree. This process restricts flow of essential water, nutrients, and sugars throughout the tree. The picture to the left: shows the exit wound of the adult bronze birch borer. Notice the D shaped hole.
Bronze birch borer is active in all of the Minneapolis metro area and surrounding areas. This destructive pest generally kills birch trees one stalk at a time (usually within 1-3 years per stalk). As you can see in the picture to the right: The dominate right handed lead was effected first and the left stalk is starting to decline.
The crown die back is a good indicator, in any tree, that it is being effected by a boring insect as they restrict flow of nutrients and water past the point that they feed on. Also, very inconsistent dieback can be another indicator invloved with insect damage. Adult insects tend to lay their eggs on the same tree they were hatched from. After that tree has been killed off the insects tend to travel to other paper birches that are near by.
Control of this insect can be done via trunk injection, base drench in some cases, and trunk spraying using insecticide. When it comes to selecting a method it is always a great idea to consult an arborist to figure out what is the best option for your tree. Trunk injections are the least harmful to the environment, and have the best results at saving your tree.