How to Tell If Your Ash Tree Has Emerald Ash Borer (EAB)

If you have an ash tree in Metro East Illinois, it is worth learning the warning signs of the emerald ash borer, because spotting them early can be the difference between a treatable tree and a hazardous, expensive removal. The beetle is relentless and it has already reached this region, so the question for most ash owners is not if but when — and how far along the damage already is.

Here are the four symptoms that matter most, roughly in the order they appear, plus what to do once you recognize them. None of these require a ladder or any risk on your part — they are all visible from the ground with a careful eye.

What the emerald ash borer is

The emerald ash borer, or EAB, is a small, metallic-green invasive beetle originally from Asia. The adults are only about half an inch long, but the real damage is done by the larvae, which feed in the layer just under the bark — the tissue the tree relies on to move water up and food down.

As generations of larvae carve their tunnels, they progressively girdle the tree from the inside, cutting off its circulation. EAB attacks all native North American ash species, and it has spread throughout Illinois, killing ash across Madison and St. Clair counties by the thousands. An untreated infested ash typically dies within a few years of the first symptoms.

Sign 1: Crown dieback starting at the top

EAB damage almost always shows first at the very top of the canopy and works its way downward, because the uppermost branches are the farthest from the roots and the first to be starved as the tree's plumbing fails. If the upper third of your ash is thinning, has bare or dead branches, or is leafing out sparsely while the lower canopy still looks reasonably full, that top-down dieback is a classic early red flag.

Compare your tree to a healthy ash if you can — the contrast in canopy fullness is often striking once you know to look for it. Crown dieback of thirty to fifty percent usually means the infestation is well established.

Sign 2: Epicormic sprouts along the trunk

As the tree struggles to survive, it often sends out desperate new shoots — called epicormic sprouts or water sprouts — directly from the trunk and lower branches, sometimes in dense clusters. It is the tree's emergency attempt to grow new leaves below the failing upper canopy and keep photosynthesizing.

Clusters of leafy growth erupting from the bark where there were no branches before is the tree's distress signal, and combined with top-down dieback it is a strong indicator of EAB rather than some other stress.

Sign 3: D-shaped exit holes

When adult beetles mature and emerge from the tree, they chew their way out through a distinctive D-shaped exit hole about an eighth of an inch across — flat on one side, rounded on the other. That specific D shape is the signature of EAB; round holes are usually made by other, less serious insects.

Finding these exit holes on the trunk and larger branches confirms an active infestation that has already completed at least one life cycle inside the tree. They can be small and easy to miss, so look closely on smooth-barked sections.

Sign 4: S-shaped galleries and woodpecker blonding

If bark is peeling or you pull back a loose piece, look for winding, S-shaped tunnels packed with fine sawdust just beneath it. These serpentine larval galleries are where the actual damage happens — each one is a severed section of the tree's circulatory system. A dense network of them means the tree is being girdled.

There is also a secondary clue: woodpeckers strip bark to eat the fat larvae, leaving patches of lighter-colored inner bark exposed, a phenomenon called "blonding." If your ash suddenly has pale, flaky patches where birds have been working, that is often EAB underneath.

Can it be treated, or does it need to go?

Timing is everything with EAB. An ash caught early, with a mostly healthy canopy and minimal dieback, can sometimes be protected with systemic insecticide treatment applied on a regular schedule. But once you are seeing heavy dieback, exit holes across the trunk, and bark loss, the tree is usually past saving — and a dead ash becomes dangerous and expensive to remove as the wood turns brittle.

At that point, a safe crane or bucket removal is the responsible call, before the tree starts dropping limbs on its own. The decision hinges on how far the damage has progressed, which is exactly what an on-site assessment determines.

Get an on-site EAB inspection

First, is it even an ash tree?

Before you worry about EAB, confirm you actually have an ash. Ash trees have opposite branching — buds and branches emerge directly across from each other rather than staggered — and compound leaves made up of five to nine leaflets on a single stem. The bark on a mature ash forms a distinctive tight diamond pattern. Relatively few common trees share the opposite-branching-plus-compound-leaf combination, which helps narrow it down.

If you are unsure, that is exactly the kind of question an arborist answers in a minute during an assessment. Confirming the species matters, because the treatment and removal decisions that follow are specific to ash.

Treatment and cost if you catch it early

For a healthy, early-stage ash worth keeping, systemic insecticide treatments can protect the tree, but they are a commitment, not a one-time fix — they are typically repeated every one to three years depending on the product, for as long as EAB pressure remains in the area. Over years, that cost adds up, so treatment makes the most sense for high-value, healthy trees in prominent locations.

The decision is a genuine cost-benefit calculation: the ongoing expense of protecting the tree versus the value it provides and the eventual cost of removing it. An honest arborist helps you weigh it rather than defaulting to either extreme.

What to do once you confirm EAB

If the signs point to an established infestation, the next step is deciding treat-or-remove based on how far it has progressed. A tree still mostly healthy may be a treatment candidate; one with heavy dieback and bark loss is a removal. Either way, do not simply wait and watch — a declining ash gets more dangerous and more expensive to handle every season.

Getting a professional eye on it early keeps all your options open. Once the wood turns brittle, the easy, affordable removal window has already closed.

How fast an infested ash declines

One reason EAB catches homeowners off guard is the speed and pattern of decline. A tree can look basically fine one year and show serious canopy thinning the next, because by the time outward symptoms appear the larvae have often been at work for a season or two already. From noticeable dieback, an untreated ash frequently goes from struggling to dead within just a few years, and the structural decline of the wood follows close behind. This is why "wait and see" is such a poor strategy with ash — the tree does not decline gently, and the safe removal window closes faster than people expect.

What to do the day you confirm it

If the four signs point to an established infestation, do not sit on the information. Decide, with professional input, whether the tree is a treatment candidate or a removal, and if it is coming out, get it scheduled while it can still be handled straightforwardly. Note any other ash on your property or your block, since they are likely on the same trajectory. And keep the safety picture in mind: an infested ash overhanging a driveway, deck, or play area is a rising hazard, not a someday project. Prompt, informed action is far cheaper and safer than the alternative that arrives on its own schedule.

Replanting after ash loss

Losing an ash is a chance to replant something the borer cannot touch. Diversifying species is the real lesson of the EAB epidemic — monocultures of a single tree let a single pest devastate a whole neighborhood's canopy. When you replace a removed ash, choosing a different, well-adapted species helps ensure the next invasive insect or disease cannot repeat the same clean sweep. We are glad to grind the old stump and talk through the property so your new tree gets a healthy start well clear of the old root mass.

The four signs of emerald ash borer

• Crown dieback starting at the top of the canopy
• Epicormic water sprouts erupting along the trunk
• D-shaped exit holes about an eighth-inch across
• S-shaped larval galleries under peeling bark
• Woodpecker 'blonding' where birds strip bark for larvae
• Opposite branching + compound leaves confirm it is an ash

Confirming it's an ash before you worry about EAB

Before diagnosing emerald ash borer, make sure you actually have an ash — a surprising number of homeowners misidentify the tree. Ash have opposite branching, meaning buds and branches emerge directly across from each other rather than staggered, and compound leaves made of five to nine leaflets on a single stem. Mature ash bark forms a tight, regular diamond pattern. Few common Metro East trees share the opposite-branching-plus-compound-leaf combination, so that pairing is your quickest confirmation.

Once you've confirmed it's an ash and spotted the signs, the decision is treat-or-remove, and it hinges on how far the damage has progressed. A tree with a mostly full canopy and minimal dieback may be a treatment candidate; one with heavy dieback, exit holes across the trunk, and bark falling away is past saving. The window closes faster than people expect, which is why an early professional look keeps your options open.

At-a-glance: quick reference

Not sure where your ash stands on the spectrum from treatable to hazardous? Our certified arborist can assess the tree's health and real risk and give you honest options rather than a default recommendation to remove. We serve Granite City, Glen Carbon, and Edwardsville. Call (855) 615-0568 to schedule an inspection before your ash makes the decision for you.