Bronze birch bore is perhaps the Midwest’s most severe pest of birch trees. The bronze birch borer is a secondary problem, meaning it usually only attacks trees already in a stressed or weakened state because of drought, disease, nutrient deficiency, or injury. Improper siting is a common reason for encounters with the bronze birch borer. Trees sited properly are often healthy and vigorous, which are less attractive to the borer and therefore more likely to survive.
This larva spends the winter in small cells beneath the bark and transforms into pupae in spring. The adults typically emerge in Wisconsin in early June and may continue into July. The adults chew their way through the bark and branches, leaving behind their iconic D-shaped exit hole – a helpful indicator to find out if you’re having problems with the bronze birch borer. Their damage causes girdling, preventing water and nutrients from moving above the attack site. Typically, it takes 3-4 years to kill the entire tree. Although, entire branches may die within only a couple of months if feeding is extensive. Trees planted in very poor sites or areas where the bug is already present may die only one year after infection.
Paper Birch is perhaps the most susceptible to the bronze birch borer among all our native birches – River Birch has the highest natural resistance to this insect pest.
Prevention is your best method of control. Making sure your birch is happy and healthy is the best thing you can do to protect the birch from this insect. For chemical treatment, we recommend you consult with an ISA Certified Arborist near you.
It’s is also susceptible to aphids, birch leaf miner, and birch skeletonizer – although these pests are minor compared to bronze birch borer.