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Bronze Birch Borer in Salem and the Willamette Valley
If your birch is dying from the top down, this beetle is the most likely reason. It has been killing birch trees in western Oregon since the early 2000s.
The short version: if a white-barked birch is thinning and dying from the top down, bronze birch borer is the likely cause. Caught early, deep watering and winter pruning can save it. Once half the crown is dead, the tree should be removed before it gets brittle. Call or text (503) 551-5141.
What is bronze birch borer?
The bronze birch borer is a slender, dark beetle with a bronze sheen. It is native to North America and has become established in the cities and towns of western Oregon. Its larvae tunnel under the bark of birch trees and cut off the flow of water and nutrients, starting in the upper branches and working down.
It goes after stressed trees first. In the Willamette Valley that usually means birch planted in full sun on a lawn that dries out in July and August. European white birch and Himalayan (jacquemontii) birch, the white-barked trees in so many front yards, are the most vulnerable.
What are the signs of bronze birch borer?
- Sparse, yellow or undersized leaves at the top of the tree
- Dead twigs and branches in the upper crown while the lower tree still looks fine
- Raised ridges or bumps on the bark where the tree has grown over the tunnels
- D-shaped exit holes in the bark of the trunk and larger branches
- Rusty stains on the white bark
What can you do about it?
Keep the tree from getting stressed. Water deeply through the dry months, keep a few inches of mulch over the roots and keep the mower and string trimmer away from the trunk.
Prune at the right time. Have dead and dying branches removed in fall or winter. Do not prune birch from spring through late summer, when the adults are flying and are attracted to fresh cuts. See tree pruning.
Decide early. A birch that has lost less than about a third of its crown may be worth trying to save, sometimes with an insecticide treatment from a licensed applicator. Once half the crown is dead the tree will not recover. Dead birch gets brittle quickly, so do not leave it standing over a house or driveway. We handle the removal and the stump.
Replant wisely. River birch, including the variety called Heritage, resists the borer and grows well here.
Oregon State University Extension publishes a good homeowner guide to managing bronze birch borer.
Bronze birch borer questions
How do I know if my birch has bronze birch borer?
The first sign is thin, yellowing leaves and dead twigs at the very top of the tree. Later you may see raised ridges under the bark and small D-shaped holes where the adult beetles came out.
Can the tree be saved?
If less than about a third of the crown is affected, sometimes, with deep watering through summer, mulch and in some cases an insecticide treatment from a licensed applicator. Once half the crown is dead, removal is usually the answer.
When should birch be pruned?
In fall or winter. Avoid pruning birch from spring through late summer, when the adult beetles are flying and are drawn to fresh cuts.
What should I plant instead?
River birch, including the variety called Heritage, is resistant to bronze birch borer and does well in the Willamette Valley.
Related
Birch dying from the top? Call before it gets brittle.
Call or text the office, or send the estimate form. Jennifer answers the phone Monday to Friday, 7 am to 6 pm.