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Bronze Birch Borer

Blog Post
Find information about the bronze birch borer insect pest.
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An Insect Pest of Birch Trees

Crown die-back, zigzag patterned bark, D-shaped holes in the trunk or branch—these are all signs of an insect pest, the bronze birch borer (BBB).

Native to the eastern side of the Oregon and across much of the US, the bronze birch borer is now an established pest in western Oregon.

BBB attacks all species of birch. Some species are more resistant than others. Unfortunately, the popular European birch (Betula pendula) is very susceptible to damage from BBB.

By the time property owners notice a birch tree in decline, it is too late. The insects, themselves, are small (1/2 inch long) and hard to spot. Watch, instead, for the following signs and symptoms of a bronze birch borer infestation.  

River Birch is Resistant to BBB

River birch (Betula nigra) is resistant to bronze birch borer. Urban Forestry plants river birch 'Heritage' and 'Dura-Heat' as part of our Free Street Tree and Yard Tree Giveaway programs.


Bronze Birch Borer Signs and Symptoms

Crown Die-back 

Dieback of birch crown
Crown die-back is a sign of bronze birch borer damage. Photo: Steven Katovich, Bugwood.org

Crown die-back is when the top of the tree starts to die while the rest of the tree still looks relatively healthy. You may notice dead leaves, broken branches, or fewer leaves than in previous years.  

The crown die-back shown in the photo is severe and the tree will need to be removed.

Zigzag Bark Pattern 

Zigzag-shaped damage from bronze birch borer larvae
Birch trees form callus tissue around the bronze birch borer larvae feeding galleries. Photo: Steven Katovich, Bugwood.org

A zigzag pattern on the bark of your tree (as shown in the photo) is a sign larvae are feasting on your tree’s cambium. Cambium is the layer of the tree between the bark and the wood. It contains nutrients and water. The larvae feed on the cambium and damage the tree.

D-Shaped Exit Holes

D-shaped exit hole in birch bark
As adult beetles exit birch trees, they form D-shaped hole. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Small, D-shaped holes are the exit points for the adult beetles after the larval feeding stage. This symptom is hard to spot and requires a close look at your tree.  


What Can you Do about BBB?

Bronze birch borer is most likely to attack old, stressed, or drought-stricken trees.

Keep you birch trees healthy by providing adequate water. See Summer Watering Tips for details.

Avoid damaging birch trees with mowers or other equipment.

Consult with an Arborist

Birch trees are lovely additions to our landscapes. Unfortunately, the bronze birch beetle agrees.

If you see any symptoms of BBB in your tree, consult a qualified tree care provider for treatment options.


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