What's happening to my birch tree? Here in the Pacific Northwest, the culprit could be a 1/2-inch long beetle called the bronze birch borer (BBB). You'll likely never see these insects. They lay eggs under the bark where the larva grow by feeding on the tree's sensitive cambium layer. Then, the adult beetle "chews" its way out and flys away to reproduce and repeat this cycle.
The first signs of BBB activity are typically wilted leaves near the top of the tree. Twig and branch dieback happen next. Later, their distinctive "D-shaped" exit holes can be found on limbs in the upper tree canopy
Typically, BBB infests birch trees that are stressed or have already begun to decline. European white bark birch (Betula pendula) is most susceptible. Paper birch (Betula papyrifera) is also vulnerable. Trees that are weakened or stressed are most susceptible to the Bronze Birch Borer. These trees evolved to grow in cool, moist conditions. In landscape settings, these trees are often planted on exposed sites with low soil moisture. Trees that have broken in a windstorm or heavily pruned are at greater risk.
Infected trees may decline for several years before dying, although they may die during a single year if conditions are particularly hot and dry. Research shows the decline of a birch tree may be reversed in the early stages but trees are unlikely to recover once 50% or more of the crown is damaged. (US Forest Service)
Oregon State University Extension: Homeowner Guide to Managing Bronze Birch Borer
What Can Property Owners Do?
Understand the damage - trees can be preserved with early interventions
Treat with insecticides - applied by a licensed tree health professional
Tree133 works with property owners in and around Seattle to preserve trees and mitigate tree hazards. If you have questions about birch trees on your property, we are ready to help. Contact us here