Emerald ash borer: treat, or remove?

Updated 2026-10-18 · 10 min read · Species & health

Woodcut of a standing dead ash, bark stripped to blond sapwood with woodpecker flecking — Bark shed off a dead ash to blond sapwood, the borer's galleries cut into the wood beneath — the sign you can read from the kerb, and by then it is late.

Emerald ash borer is not a disease you manage — it is a beetle whose larvae eat the layer that moves food up and down the trunk. The question is never "can this be cured". It is whether this particular ash is worth a treatment programme, and that is answered by looking up at the canopy.

What to look for, in the order you will see it

Thinning at the top of the canopy, working downward.
Blond patches on the bark where woodpeckers have flaked it off chasing larvae.
Epicormic sprouts — shoots straight out of the trunk, the tree's panic response.
D-shaped exit holes about an eighth of an inch across, and serpentine galleries under lifted bark.

Watch

By the time exit holes are easy to find, the larvae have been feeding for a while. Iowa State extension says decline typically runs two to four years, and can take as little as one. The visible timeline lags the real one badly.

The threshold that decides

Canopy condition	Treatment prognosis	Sensible action
Full, healthy	Good	Treat on cycle if the tree is worth it
Some thinning, under 50%, under 30% of branches dead	Fair, declining	Still a candidate: treat now or plan the removal now
50% thin or more, or 30%+ branches dead	Poor	Iowa State: no longer a treatment candidate; remove
Small leaves across the whole crown	None	Remove while climbing is still safe

The threshold exists because treatment is systemic: it has to move through conducting tissue the larvae have already been eating. Below a certain amount of functioning canopy, the tree cannot distribute the product that would save it.

Woodcut illustration: emerald ash borer treatment, step one — A D-shaped exit hole and the serpentine gallery behind it — the signature under lifted bark.

How treatment works

The mainstream method is trunk injection at the root flare, which puts a systemic insecticide directly into the vascular system and avoids soil and drift exposure. Iowa State extension says applications are needed every one to two years depending on the product, so this is a repeating cost for the life of the tree, not a one-off.

Product names, rates and re-treatment intervals change and are regulated per state. Confirm the current label with your state extension service or a licensed applicator; this page does not name a product or a price because neither could be verified live at the time of writing.

The money question, honestly framed

The labour under both options is the same arithmetic as everywhere on this site: BLS puts the hourly mean for tree trimmers at $26.91 (OEWS, May 2025), which loads to roughly $41.71 per crew-member hour. Injection is a short visit repeated every few years; removal is a big single visit that also removes the shade, the screen and the property value.

The comparison to run is total treatment cost over the years you expect to stay, against the removal cost plus the value of what is lost, which is what the appraisal calculator exists to estimate. For a large ash shading a house, treatment often wins that comparison comfortably — for a small one in a back corner, it rarely does.

Woodcut illustration: emerald ash borer treatment, step two — An injection port set at the root flare of a healthy ash: the whole treatment, repeated every few years.

Why a dead ash gets expensive

Ash killed by EAB goes brittle unusually fast. Within a couple of years the limbs will not hold a climber and the wood fails without warning under rigging loads, which pushes the job from a climbing removal into a crane or lift removal — a different and larger invoice.

That is the hidden cost of deferring the decision: the same tree removed three years late costs materially more than removed today. If the canopy is already past half, run the risk form and get it booked.