Two-Lined Chestnut Borer: Atlanta Identification & Treatment Guide

What Is Two-Lined Chestnut Borer?

Two-lined chestnut borer (Agrilus bilineatus) is a native North American wood-boring beetle in the family Buprestidae whose larvae tunnel under the bark of oak trees, cutting off the flow of water and nutrients. It is considered a secondary pest, meaning it typically attacks oaks already weakened by drought, construction damage, defoliation, or poor soil conditions.

How to Recognize It

• Wilted or browning leaves in the upper canopy in mid to late summer, often with dead leaves still clinging to the branches.
• Branch dieback that starts at the top of the tree and progresses downward over one to three years.
• Small D-shaped exit holes (about 1/8 inch wide) in the bark of the trunk and larger branches.
• Sparse, undersized, or yellowing foliage compared to neighboring healthy oaks.
• S-shaped or serpentine tunnels (galleries) under the bark, visible only if loose bark is peeled back.
• Sudden decline in an oak that recently went through drought, root damage, or heavy defoliation.

Adult beetles emerge and lay eggs from late spring into early summer, roughly when black locust blooms. The most visible symptom, browning leaves in the upper canopy, typically shows up in mid to late summer of the same year the tree is attacked.

Why It Matters for Atlanta Trees

This pest is serious. Infested oaks commonly die within two to three years, and decline can be even faster when other problems like oak wilt or root disease are present. Because the borer attacks the upper canopy first, branches die in place and can drop, posing a real risk to people, vehicles, and structures below. In Atlanta yards, the oaks most often affected include white oak, northern red oak, scarlet oak, chestnut oak, black oak, post oak, and water oak when stressed, which covers a large share of the mature shade trees on local properties.

General Prevention

• Water established oaks deeply during drought, especially in mid to late summer, to keep them from sliding into the stressed state that attracts borers.
• Maintain a wide ring of organic mulch (2 to 4 inches deep, kept off the trunk) over the root zone to conserve moisture and protect roots.
• Protect oak roots and trunks from construction damage, soil compaction, and grade changes, which are leading triggers of borer attack in Atlanta yards.
• Avoid pruning oaks during the adult beetle flight period in late spring and early summer, when fresh wounds can attract egg-laying females.

What NOT to Do

• Do not self-diagnose. Many tree problems look alike, and treating the wrong one wastes time and can harm the tree.
• Do not apply fungicides, insecticides, or other chemicals without an arborist's specific recommendation. Wrong product or wrong timing makes things worse.
• Do not leave dead or dying oaks standing near homes, driveways, or play areas while you decide what to do. Upper-canopy limbs killed by this borer can fall without warning, so have a qualified arborist assess the hazard promptly.

Related Services

For most diagnosis and treatment questions, the right starting point is one of our services:

• ISA-Certified Arborist Services: diagnosis, consultation, second opinion
• Plant Health Care (PHC): ongoing tree health management
• TRAQ Tree Risk Assessment: when the tree may be a safety hazard

Sources

This page summarizes general information from: NC State Extension, University of Minnesota Extension, and University of Kentucky Forestry and Natural Resources Extension.