Learn how to identify the bronze birch borer insect. See the tree damage signs to look for and the recommended treatment.
Bronze Birch Borer: Tree Damage and Treatment
Published on Apr. 15, 2025
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Tree Damage From Bronze Birch Borer
“Last spring, only the bottom of my 15-year-old birch tree had leaves. The upper branches were green and flexible, so I don’t think they were dead. There was also dark sap running down the trunk. What happened?” asks Birds & Blooms reader Cindy Ortmann of Bismark, North Dakota.
Gardening expert Melinda Myers says, “Bronze birch borer is the most common pest of paper bark birches. The wormlike borer feeds under the tree bark, and the feeding eventually blocks the flow of water and nutrients to the leaves and branches. This results in stunted growth, defoliation and dieback starting at the top.
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Signs of Infestation
Melinda says, “To confirm borer presence, look for D-shaped exit holes and raised areas on the branches and trunk. The oozing red sap is another indication of an infestation.
Bronze Birch Borer Treatment
“Severely infested trees with more than one-third dieback may be difficult to save,” Melinda says. “A mild infestation is treatable with a systemic insecticide labeled for bronze birch borer. Consider hiring a certified arborist (treesaregood.com is a reliable resource) who has access to effective chemicals and equipment and the experience to treat for this pest.”
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Pest Prevention
Paper bark birch trees (Betula papyrifera) prefer cool, moist summers like those in their native habitat of northern North America. When planted in areas with hot, dry summers, the trees may become stressed and more susceptible to the pest.
As an alternative, the river birch tree (Betula nigra) tolerates both wet and dry soil and is resistant to the bronze birch borer.
About the Expert
Melinda Myers is the official gardening expert for Birds & Blooms. She is a TV/radio host, author and columnist who has written more than 20 gardening books. Melinda earned a master’s degree in horticulture from the University of Wisconsin-Madison.
