Bronze Birch Borer has been a serious pest of birch trees. Its preferred host is European white birch. Paper, yellow and gray birch are also attacked but to a lesser degree. Like most wood-boring beetles, the bronze birch borer is really a secondary problem. They usually attack trees under stress or in a weakened condition.
The first sign of an attack is usually the thinning or dieback of branches in the uppermost part of the tree. Leaves on the infested branches may be unusually small or show browning along the edges. Larvae cause the damage by feeding under the bark and girdling the branches or trunk. Girdling prevents movement of food and water to tissue above the attack site. This interruption causes swollen bands or ridges in the affected trunks and branches. A gradual decline of the birch and eventual death will happen within two years.
In winter, they spend their time as larvae in small cells just beneath the bark. The larvae pupate in spring and adults emerge from May through July. Adults will chew their way through the bark, leaving a D-shaped exit hole. The females live for three weeks and deposit eggs under loose bark or in cracks or crevices on the trunk. Eggs will hatch in about two weeks, and the larvae will bore into the tree to begin feeding on the inner and outer bark. The tunnels behind active feeding larvae become packed with excrement and wood particles which turn dark brown with age. Pupation occurs in April and May the following spring and there is only one generation a year in Michigan.
Just remember to keep a mindful eye on your trees, shrubs and plants. If you see something that doesn’t look “normal”, contact a Branch Tree & Landscape Service certified arborist.
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