Emerald Ash Borer Has Reached Greater Portland

First, Do You Actually Have Ash?

Half the calls about this beetle come from people who do not have ash, and a quiet share come from people who have several and never knew. Ash is easy to confirm once you know the three tells: branches and buds grow directly opposite each other (most yard trees alternate), the leaves are compound with five to eleven leaflets on a single stem, and mature bark carries a tight, regular diamond pattern. Ash is one of the most common street and yard trees in Greater Portland, so a lot of Falmouth, Cape Elizabeth, and in-town Portland lots have one or two without the owner ever thinking about it. Maine also has brown ash (black ash) in wet ground, the tree Wabanaki basketmakers have relied on for generations, which makes this loss cultural as well as botanical.

Why This One Is Different From Every Other Tree Problem

Most pests and diseases weaken a tree and let it fight back. Emerald ash borer does not negotiate. The adult beetle lays eggs on the bark; the larvae tunnel underneath and carve S-shaped galleries through the exact layer that carries water and sugar up and down the trunk. Enough larvae, and they girdle the tree from the inside. In an infested area, mortality of untreated ash runs close to total over a handful of years. This is not a "maybe it pulls through" situation, and that is what makes early identification worth your attention.

It Is Not a Distant-Maine Story Anymore

Emerald ash borer is now established across southern Maine, and Cumberland County (all of Greater Portland) sits inside the state's ash quarantine zone. Detections in 2026 reached nearby Harpswell, Topsham, and Bowdoinham, which is close enough that local ash trees are at genuine risk now rather than eventually. The beetle spreads partly by hitching a ride in moved ash firewood, so the practical homeowner rule is simple: do not haul ash wood around the state, and buy or burn firewood locally. (Maine has restricted moving ash wood for years; as of mid-2026 the state has proposed winding that quarantine down because the beetle is now too widespread to contain, so the rules may loosen even as the risk to your tree does not.)

The Signs, From Subtle to Impossible to Miss

• Thinning from the top down. The upper third of the crown leafs out sparse while the lower branches look fine. This is usually the first real symptom, and it is easy to write off as a dry summer.
• Sprouts low on the trunk. A stressed ash throws out clusters of new shoots from the base and trunk, a last effort that looks almost healthy and means the opposite.
• Woodpecker blonding. Woodpeckers strip the outer bark to reach the larvae, leaving pale flecking on the upper limbs. On a bare winter tree it can be the very first thing anyone notices, often before any other sign.
• D-shaped exit holes, about an eighth of an inch, with one flat side, where adult beetles chewed out. Splitting bark and the shallow, winding S-galleries underneath confirm it.

Here is the hard part: by the time the canopy is visibly dying, the infestation is usually well along. That timing is exactly why a professional assessment is worth it while the tree still looks mostly fine, because the decision that follows depends entirely on how far it has already gone.

Treat or Remove: The Honest Version

There are only two real paths, and the right one depends on the specific tree. Treatment means a systemic insecticide, injected into the trunk by a licensed applicator and repeated every two to three years for the life of the tree. It genuinely works, but it is worth the ongoing commitment only for a healthy, well-placed, valued ash caught early, before it has lost roughly a third of its canopy. Past that point, the tree rarely recovers even with treatment.

Removal is the honest answer for ash that is already declining, poorly placed, hanging over the house, or simply not worth a lifetime of injections. There is no shame in it; a lot of Greater Portland ash is going to come down over the next several years, and doing it on your schedule beats doing it on the beetle's. A licensed arborist can tell you honestly which category your tree falls into rather than selling you one answer.

The Real Reason Not to Wait: Dead Ash Turns Dangerous Fast

This is the part homeowners underestimate. Ash does not die gracefully and stand there patiently. Dead ash goes brittle unusually fast, faster than most other hardwoods, and standing dead ash is one of the most hazardous trees there is to take down: limbs and even the trunk can fail without warning, the wood is unsafe to climb, and a crew often has to reach it from a bucket or a crane instead. Every month a dead ash stands, the removal gets more dangerous and more expensive, and the odds of it dropping a limb on its own go up. A green, structurally sound ash is a straightforward removal. The same tree two winters dead is a different and pricier job. If the decision is going to be removal anyway, earlier is cheaper and safer, full stop. (Grinding the stump afterward lets you replant with something the next beetle will not touch.)

The Short Version

Confirm whether you have ash. If you do, get eyes on it while it still looks healthy, because the treat window closes early and the danger window opens late. Treat the trees worth treating, remove the ones that are not, and do not let a dead ash stand a season longer than it has to. While you are thinking about pests the tree tools miss, southern Maine's other invasive problem is the one that comes after you, not your trees: see the browntail moth guide.