If your ash tree is still standing, here's what to do next.

What emerald ash borer actually does

Emerald ash borer (EAB) is a metallic green beetle native to Asia that arrived in the US around 2002 and has since killed hundreds of millions of ash trees across North America. The beetle itself isn't the killer — its larvae are. Female EAB beetles lay eggs in the bark of ash trees, and when the eggs hatch, the larvae feed on the layer of tissue (the phloem and cambium) just beneath the bark that the tree uses to move water and nutrients. As the infestation grows, this feeding creates S-shaped galleries under the bark that eventually girdle the tree, cutting off its ability to sustain itself. A heavily infested ash tree typically dies within 3–5 years of initial infestation.

How to tell if your ash tree is infested

The signs of EAB are specific enough that you can do a preliminary check yourself before calling an arborist. Look for these indicators:

• Canopy dieback starting at the top — EAB infestations typically thin the upper canopy first, then work downward
• S-shaped galleries visible if you peel back a small section of bark — these are the feeding tunnels of the larvae
• D-shaped exit holes in the bark, about 1/8 inch across — this is where adult beetles emerge in late spring
• Vertical bark splits — the tree's response to larval feeding pressure underneath
• Epicormic sprouting — small shoots erupting from the main trunk or large branches, which is the tree's stress response

If you're seeing the top 25–30% of the canopy thinning out on an ash tree, get an assessment quickly. The treatment window is real but it closes.

The treatment window — and what it costs

Ash trees with less than 50% canopy decline and no significant bark loss (no large areas where bark is separating or falling away) are still candidates for systemic insecticide treatment. The most effective treatments use emamectin benzoate, injected directly into the tree's vascular system, which provides 2–3 years of protection per treatment. A single treatment on a medium-sized ash tree runs $150–$350 depending on trunk diameter; ongoing protection requires repeat treatment every 2–3 years.

Trees with more than 50% canopy decline, extensive bark loss, or significant gallery coverage are generally past the window where treatment is cost-effective. At that point, removal and replacement is usually the right call — and we'll tell you that honestly rather than sell you a treatment that won't work.

The bottom line: if you have ash trees on your property in the Columbus area and you haven't had them assessed, do it this spring. EAB is in every county in Ohio. The earlier you catch it, the more options you have.