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Bronze Birch Borer

The adult bronze birch borer is a greenish bronze beetle 1/4 -1/2 inch long. The slender white larvae are about 3/4 inch long.

Habit

Adults lay eggs in May and June in bark cracks or crevices and about 10 days later, larvae hatch and bore into the wood. Larvae feed on interior tissue just under the bark and form tunnels and burrows. Often the tunnels are very crooked, cross and recross. They remain active until fall and overwinter in cells constructed at the end of their tunnels. The following spring, the larvae pupate and emerge as adult beetles through small D-shaped holes that are cut in the bark. There is only one generation per year.

Bronze birch borer damage

Bronze birch borer damage

Damage

When the larvae tunnel just under the bark, they form feeding galleries filled with frass that girdle the trunk or branch and reduce or completely stop the flow of plant sap. This injury may create a raised, rippled and bumpy surface on the bark. An early symptom is a yellowing and thinning of the leaves in the upper crown. Later, if left uncontrolled, the infestation can move downward and kill the entire tree.

Control

Non-chemical: Avoid planting white birch that is highly susceptible to this pest in Illinois home yards. Select birch trees that show resistance to this pest, such as river birch. The U.S. National Arboretum reports resistance by the river birch variety 'Heritage' and Betula platyphylla japonica'Whitespire.' Keep trees vigorous and healthy with proper siting and good cultural practices such as proper watering and fertilizing practices. Using organic mulch across the root zone helps keep roots cool.

Chemical: Insecticide may be applied in late spring early summer. Contact your county Extension office for current pesticide controls.