Treatment: Bronze Birch Borer

Expert tree pest diagnosis and treatment from Tree Care Enterprises — serving Rockford, IL and Northern Illinois since 1978.

If the birch trees on your Rockford-area property have been thinning at the top, or if branches are dying back progressively from the crown downward, Bronze Birch Borer may be the cause. This native beetle is one of the most destructive insects affecting birch trees in Northern Illinois and Southern Wisconsin, and it has accelerated its damage across the region as birch populations have been stressed by drought and warmer growing seasons.

What Is Bronze Birch Borer?

Bronze Birch Borer (Agrilus anxius) is a metallic wood-boring beetle in the same family as Emerald Ash Borer. Adult beetles are slender, olive-bronze in color, and about ¼ to ½ inch long. They emerge in late May through July, feed briefly on birch foliage, and then females lay eggs in bark crevices. The larvae — which do the actual damage — bore into the inner bark and create winding galleries that disrupt the tree’s vascular system.

Which Birch Species Are Affected?

All birch species are susceptible, but some are significantly more vulnerable than others:

• European White Birch (Betula pendula) — Highly susceptible; frequently planted in Illinois landscapes but struggles in Midwest heat and drought
• Paper Birch (Betula papyrifera) — Native to cooler climates; susceptible when stressed by heat
• River Birch (Betula nigra) — Most heat-tolerant and least susceptible; the preferred species for Northern Illinois plantings
• Heritage River Birch — Bred for heat and drought tolerance; the most BBB-resistant option for Midwest landscapes

Signs of Bronze Birch Borer Infestation

Bronze Birch Borer attacks stressed trees first — particularly those suffering from drought, soil compaction, or poor site conditions. Symptoms progress in a predictable pattern:

• Dieback from the top down. Crown thinning and branch death beginning at the top of the tree and working downward over multiple seasons.
• D-shaped exit holes. Tiny, flat-sided D-shaped holes in the bark where adult beetles have emerged. These are diagnostic for borer activity.
• Serpentine galleries. Irregular, winding galleries visible in the inner bark beneath peeling or damaged outer bark.
• Bark swelling or splitting. The cambium layer responds to larval feeding with callus tissue formation, which can cause visible ridges or splits in the outer bark.
• Yellowing or sparse foliage. Canopy stress visible as smaller-than-normal leaves, early fall coloration, or reduced leaf density.

Treatment Options

Treatment is possible for trees that still retain a significant live crown — generally trees with 50% or more of their canopy intact. Trees with severe crown loss or extensive gallery damage in the lower trunk are typically not treatable and should be evaluated for removal to prevent hazard.

Systemic insecticide treatments: Soil-applied or trunk-injected systemic insecticides — similar to those used for EAB — are the most effective management option. These products move through the tree’s vascular system and are ingested by larvae feeding in the inner bark. Emamectin benzoate (TREE-age®) and imidacloprid-based products are commonly used, with treatment frequency and timing determined by product and tree condition.

Preventive treatment for high-value trees: In areas where BBB is active, preventive systemic treatment of healthy, high-value birch trees — especially stressed European White Birch — can extend their life significantly. Our arborists can help you assess whether your trees are candidates for preventive care.

Improving tree health: Because BBB targets stressed trees, improving overall tree vigor through proper watering, mulching, and soil care can meaningfully reduce a tree’s vulnerability — especially during drought years.

Species replacement planning: For properties with highly susceptible European White Birch trees in decline, our arborists can help develop a phased replacement plan using more resilient species suited to Northern Illinois conditions.

When to Call a Certified Arborist

If you’ve noticed yellowing from the top down, thinning foliage, or D-shaped exit holes in your birch trees, don’t wait. Tree Care Enterprises’ certified arborists can assess your trees, determine the extent of any infestation, and recommend the most effective treatment plan. We serve Rockford, Machesney Park, Loves Park, Rockton, Belvidere, and the surrounding Northern Illinois and Southern Wisconsin region.

Contact Tree Care at (815) 965-5757 to schedule your consultation.

→ View our Tree Pest Management services — ISA Certified Arborists diagnosing and treating Bronze Birch Borer & other invasive insects since 1978.