Two-Lined Chestnut Borer: Atlanta Identification & Treatment Guide

What Is the Two-Lined Chestnut Borer?

The two-lined chestnut borer (Agrilus bilineatus) is a native flatheaded wood-boring beetle and one of the most serious secondary pests of oaks in the Atlanta area. The adult beetle is small (about 1/2 inch long), slender, and dark with two light-colored stripes running along its back. While native and normally present at low levels, two-lined chestnut borer populations explode when oaks are stressed by drought, defoliation, construction damage, or other environmental insults. In stressed trees, larvae girdle branches and trunks by feeding beneath the bark, often killing trees that might otherwise have recovered from the original stress.

How to Identify Two-Lined Chestnut Borer Damage

Damage from this borer follows a predictable pattern:

• Top-down crown dieback: Dieback begins at the top of the canopy and progresses downward over one to several seasons. This pattern distinguishes borer damage from many diseases that cause scattered or lower-canopy symptoms.
• D-shaped exit holes: Adult beetles emerge through small, D-shaped exit holes in the bark — similar to but smaller than those made by the emerald ash borer. These holes are most visible on smooth-barked upper branches.
• Larval galleries: Peeling bark from affected branches reveals winding, serpentine galleries packed with fine frass where larvae have fed in the cambium layer.
• Bark splitting: On heavily infested white oaks, water oaks, willow oaks, and live oaks, bark may crack and split over extensive gallery networks.

Treatment & Prevention

Because two-lined chestnut borer targets stressed trees, prevention through proper tree care is the foundation of management:

• Maintain tree health: Consistent deep watering during Atlanta's summer droughts is the single most effective preventive measure. Healthy oaks resist borer attack.
• Protect roots during construction: Root damage and soil compaction from construction activity are major stress triggers that predispose oaks to borer infestation. Establish tree protection zones before any work begins.
• Trunk injection: For high-value oaks and maples at risk, professional trunk injections with emamectin benzoate can provide preventive protection against borers for one to two years.
• Prompt removal of dead branches: Remove and destroy infested branches before adult beetles emerge in spring to reduce local borer populations.
• Avoid stress stacking: Do not heavily prune, fertilize with high nitrogen, or disturb the root zone of oaks already under drought stress — additional stressors compound borer vulnerability.

When to Call an Arborist

If you notice progressive crown dieback or D-shaped exit holes on any oak, contact an ISA-certified arborist for assessment. Early intervention — including stress reduction, preventive trunk injection, and plant health care — can save trees that are in the early stages of infestation. A tree risk assessment can determine whether heavily infested trees pose a hazard. Call EastLake Tree Services at 404-850-1174 or request a free quote.