Bronze Birch Borer: Why Rochester Birches Die From the Top Down

By Linda Marsh, Pests & Diseases. Last updated: July 9, 2026.

If your birch is in trouble, here is what homeowners tend to notice first:

• Thinning and dead branch tips at the very top of the crown
• Sparse, undersized, or off-color leaves in the upper canopy
• Small, raised ridges or lumps running along the bark of dying limbs
• Leafy sprouts pushing out from the lower trunk while the top declines

Why is my birch dying from the top down?

When a white-barked birch thins and dies back starting at the very top of the crown, the most likely culprit across the Rochester area is bronze birch borer (Agrilus anxius). This is a native North American beetle, not an invader like emerald ash borer, and it is a longstanding pest of ornamental birches. As Ohio State University Extension entomologist Joe Boggs explains, "Our native birch trees co-evolved with BBB and vice versa, so natural selection favored native trees that have a defense against BBB," which is exactly why the imported white birches Rochester homeowners love are the ones that die (Ohio State University Extension / BYGL).

The visible damage comes from the larvae, not the adult beetle. After adults lay eggs in bark crevices, the larvae tunnel winding, S-shaped galleries through the vascular tissue just under the bark. Those galleries girdle branches from the inside, cutting off water and nutrients. Because the borer tends to colonize the thin-barked upper limbs first, the top of the tree starves before the lower canopy does. That is why the classic fingerprint is dieback that starts at the crown and works downward year after year. If you are still trying to work out what is wrong with a struggling tree, our guide on why your tree is sick walks through how to read decline before you assume the worst.

What are the signs of bronze birch borer?

The clearest confirmation is a small, capital-D-shaped exit hole in the bark, roughly 3/16 inch wide, left where an adult beetle chewed its way out (UNH Extension). The adults themselves are easy to miss: slender metallic beetles, with males about 3/8 inch long and females about 1/2 inch, producing one generation per year in most of our climate (The Morton Arboretum). You are far more likely to see the damage than the insect.

Watch for this cluster of symptoms, roughly in the order it appears:

• Top-down canopy dieback. Sparse leaves and bare branch tips in the upper third of the tree while lower limbs still leaf out.
• Raised ridges and lumps. As the tree tries to wall off larval galleries, it forms calluses that leave swollen ridges snaking along the bark of affected limbs.
• Rusty or brown staining. Weeping or discolored streaks sometimes mark the bark over active tunnels.
• D-shaped exit holes. The flat-sided D distinguishes these borers from round-holed insects and confirms adults have emerged.
• Epicormic sprouts. Leafy shoots erupting from the lower trunk are a stressed tree's last-ditch attempt to keep growing while the crown fails.

That D-shaped hole is a family trait of Agrilus borers. The same flat-sided D shows up on ash killed by emerald ash borer in Monroe County, so the host tree matters: bronze birch borer only attacks birch. Early canopy symptoms can also be confused with ordinary drought stress, and a birch that starts dropping leaves early in a dry Rochester summer may be stressed, infested, or both.

Which birches are most at risk in Upstate New York?

Susceptibility tracks closely with where the birch evolved. The Morton Arboretum rates Betula pendula (European white birch) as highly susceptible and Betula nigra (river birch) as highly resistant, with paper birch and gray birch listed among the species that show some resistance (The Morton Arboretum). That is bad news for Rochester, because the graceful white-barked European birches planted in so many yards sit at the top of the risk list.

The stakes are not subtle. In a Rutgers resistance trial, "European white, mountain, and Asian white birch species were all dead in the experimental plots in less than 10 years," while native North American birches held on (Rutgers Cooperative Extension). Resistance, though, is not automatic. It depends heavily on the tree's condition. Rutgers Cooperative Extension entomologist Steven K. Rettke notes that "adult beetles will be attracted to susceptible trees that are genetically defenseless or are compromised from stress (e.g., especially drought stress)." In other words, stress is the trigger that lets the borer in, which is why a birch baking on a hot, dry Monroe County lawn is in far more danger than the same species tucked into a cool, moist, mulched bed.

Can an infested birch be saved?

Sometimes it can, and timing decides everything. A valued birch caught early, while it still holds most of its canopy, can often be protected with a systemic insecticide applied by a licensed professional, typically as a soil drench or trunk injection that moves into the branches and kills larvae as they feed. Treatment makes the most sense when the tree is structurally sound, well placed, and has lost less than roughly a third of its crown, and when the owner is prepared to keep the tree watered and monitored.

Once the borer has girdled the upper canopy and dieback passes the halfway mark, the odds of a meaningful recovery drop sharply, and money is usually better spent on removal and replanting with a resistant species. This treat-versus-remove judgment is genuinely hard to eyeball, because a birch can look "half dead" and be either recoverable or beyond saving depending on where the damage sits. A certified arborist can measure the percentage of crown lost, check for active galleries, and give an honest recommendation rather than a guess. Monster Tree Service of Rochester runs a plant health care program built for exactly this kind of insect-and-disease call.

How do you prevent bronze birch borer?

Prevention, not spraying, is the real control, and it comes down to keeping birches unstressed. Because drought stress is what invites the borer in, water is the single most important tool. Rutgers found that when available water was cut to less than half an inch per week, the resistance of even tolerant birches to the borer fell significantly (Rutgers Cooperative Extension). A few practical moves protect most Rochester birches:

• Right species, right site. Plant birches out of hot, dry lawn exposures and into cooler, moist ground. If you are planting new, choose river birch or another resistant type over European white birch.
• Deep, regular watering in drought. Soak the root zone during dry Finger Lakes summers rather than relying on a sprinkler's light sprinkle.
• Wide wood-chip mulch. A broad ring of mulch keeps roots cool and moist and cuts lawn competition, without piling it against the trunk.
• Replace chronic decliners. A European white birch already thinning from the top is usually worth replacing with a resistant species rather than fighting a losing battle.

None of this requires chemicals, and all of it makes the tree a poor target. For a birch that is already valuable and already stressed, a certified arborist can pair these cultural steps with monitoring and, where it is warranted, treatment.

FAQ

Is it too late once I see D-shaped exit holes?

Not automatically, but the holes mean adults have already emerged and the tree has been infested for at least a season. What matters is how much canopy remains. If the crown is mostly intact, systemic treatment paired with better watering can still help; if dieback is past roughly the halfway point, removal is usually the smarter investment.

Will cutting off the dead branches stop the borer?

Pruning out dead and dying wood is worth doing for safety and appearance, but on its own it does not stop bronze birch borer, because active larvae are also tunneling in living tissue you cannot see. Prune to clean up the tree, then address the underlying stress and, if the birch is valuable, have an arborist assess treatment.

Are river birches immune to bronze birch borer?

River birch is not perfectly immune, but it is the most resistant landscape birch and is rarely a serious host when it is reasonably healthy. It is the go-to replacement for a failing European white birch in the Rochester area, especially on sites that tend to run hot and dry.

Should I remove a birch that is mostly dead?

Yes. A birch that has lost most of its canopy will not recover, and standing dead limbs become a falling hazard over time. Removing it and replanting a resistant species protects both your safety and your landscape, and a certified arborist can confirm the tree is truly beyond saving before you commit.

Sources

• Monster Tree Service of Rochester
• The Morton Arboretum: Bronze Birch Borer
• Rutgers Cooperative Extension: Native White Birches and Their Resistance to the Bronze Birch Borer
• Ohio State University Extension / BYGL: Bronze Birch Borer
• University of New Hampshire Extension: Bronze Birch Borer Fact Sheet