D-Shaped Holes in the Bark of an Ash
A clean D-shaped hole an eighth of an inch across, flat on one side and curved on the other. Nothing else here cuts that shape. It is an exit wound, so larvae have fed under the bark for years.
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How to Tell Emerald Ash Borer From Other Causes of Holes in Bark
Get it identified free
It is emerald ash borer if
The hole is D-shaped and the tree is an ash
The hole has a flat side
Round holes are other borers. The flattened D comes from the beetle's own body shape and is the most reliable field sign there is.
The tree is an ash
Opposite branching, compound leaves with five to nine leaflets, diamond-patterned bark. This insect uses nothing else here.
There are S-shaped tunnels under the bark
Lift a loose flake and look for winding galleries packed with fine sawdust. Those galleries are what cut the tree's plumbing.
The upper crown is thinning
Dieback starts at the top because that is the farthest the tree pushes water. Holes plus a thin top is the whole picture.
It is something else if
The holes are round, in rows, or on the wrong tree
The holes are round
Round exit holes belong to other wood borers, and on a non-ash usually mean the tree was already in trouble.
They are in neat horizontal rows
Sapsucker. A bird drilling rings of small pits to drink sap. Ugly, largely harmless, and no treatment applies.
There are pitch tubes or sawdust piles
Bark beetles pushing material out. A different insect, usually a symptom of drought rather than a cause.
The tree has alternate branching
Then it is not an ash and not emerald ash borer, whatever the holes look like. Identify the tree first.
Where to Look for Emerald Ash Borer on an Ash Tree
Ash borer treatment
Bark splits on the trunk
Vertical cracks exposing the galleries underneath. Often the first thing visible from the ground.
Blond patches on the upper limbs
Woodpeckers stripping bark to reach larvae leave a pale, flecked look, a year or more before any exit hole.
The top third of the crown
Count how much of the upper canopy still has leaves. That number decides whether treatment is worth the money.
Sprouts at the base and along the trunk
A tree throwing shoots low down is rebuilding a canopy it can no longer supply. A distress signal, not new growth.
Send a photo of the tree and one of the damage. An arborist will name it before anybody drives out.
The same ash, left alone
Year one
Nothing visible from the ground. Larvae are feeding in the phloem and the tree looks entirely normal from the driveway.
Year two
Slight thinning at the top and a few blond woodpecker patches on the upper limbs. The last easy year, and almost nobody catches it.
Year three
Exit holes appear, bark splits open, and the upper crown is visibly thin. Treatment can still hold a tree from here.
Year four
Half the canopy or more is gone, sprouts are coming out of the trunk and root flare, and injections stop making economic sense.
Year five
A standing dead ash. The wood goes brittle fast, which turns an ordinary removal into a crane job and moves it up the price range.
A dead ash does not wait politely. It is one of the fastest species to become dangerous to climb, so removal costs more the longer the decision sits.
The Spring Injection Window for Treating Emerald Ash Borer
Ash borer treatmentOne year, December through November
Dormant, nothing moves
December through March
No transpiration, no distribution. An injection now would sit in the base of the trunk and go nowhere useful.
Leaf-out, the window opens
April into May
Canopy expanding, soil still holding spring moisture, uptake fast and even. Most ash work is scheduled here.
Peak injection weeks
Mid May through June
Full canopy, strong water movement, and material in place before this year's larvae start feeding.
Adults flying and laying eggs
Late June into July
Beetles are out on the bark. Trees treated in spring are protected, and a trunk in dry July soil takes up material poorly.
Larvae feeding, unseen
August through November
This year's damage is being done under the bark and nothing applied in fall reaches it. Plan the spring instead.
Treatment runs on a two-year cycle for the life of the tree. Skipping a cycle does not pause the problem, it restarts it.
What Waiting to Treat Emerald Ash Borer Really Costs
See pricing
Injection every second year on a full-canopy ash
Routine
A recurring cost that keeps a mature shade tree standing. On a good specimen in a good spot, the cheapest outcome.
Injecting an ash that is already a third bare
Same cost, worse odds
Same material, same schedule, less plumbing left to distribute it. Some hold. Some decline anyway and the money is gone.
Removal and replanting
$1,000 – $8,000
Higher within that range once the tree is dead and brittle, because it becomes a crane and rigging job rather than a climb.
Removal figures are Eden's published range and vary with size and access. Injection cost varies with trunk diameter, since the dose is calculated from it.
“This is the second year I have had them help me with my trees. They do a great job and I will stay with them in the future. DJ was wonderful.”
Common questions about emerald ash borer
Ask us something elseCan you save a tree that already has exit holes?
Sometimes. It depends on how much canopy is left, not on the holes. A mostly full crown with a handful of exit holes often responds well. A tree that has lost half its canopy has too little vascular system left to distribute material, and we will say so.
Is this preventable or curable?
Preventable. Injection protects the tissue the tree grows and kills larvae feeding in treated wood, but it does not repair galleries already cut. That is why treating early is cheap and treating late is a gamble.
How often does it have to be done?
On a two-year cycle, indefinitely. The insect is established here permanently, so an untreated ash is exposed every year it stands. Anyone calling this a one-time fix has misunderstood it or is not telling you the whole thing.
What is woodpecker flecking?
Woodpeckers strip thin outer bark off upper limbs to reach larvae, leaving pale patches that look sanded. It shows up a year or more before exit holes. Blond upper limbs on an ash are a reason to call.
Should I treat or remove?
It comes down to the tree's condition, size, what it shades, and how long you plan to be in the house. A large healthy ash over a west-facing roof justifies decades of injections. A small crowded ash at the fence line does not.
Are the do-it-yourself soil drenches worth trying?
On a smaller ash a soil-applied product can give partial protection, and they are legal for homeowners to apply. Uptake on a large tree in heavy clay is inconsistent, and over-the-counter products are weaker than what a licensed applicator injects.
Is my ash a risk to the house if it dies?
More than most species. Ash killed by borer goes brittle unusually fast, and dead limbs shed without warning in wind or ice. A dead ash over a roof, driveway or play area moves ahead of almost anything on a removal list.
Identification is free, including when the answer is that the tree needs nothing.
Related Ash Tree Symptoms and Services for Emerald Ash Borer
All tree problems
Thinning at the top of the canopy
The symptom that arrives before the holes do.
Emerald Ash Borer Treatment
What gets injected, on what cycle, and what it costs to keep up.
Borer Control
The other trunk and branch borers that turn up on stressed trees here.
Tree Removal
For the ash that is past treating, and why waiting raises the price.
Tree Planting
What goes in the hole afterward, and why it should not be another ash.
Why D-Shaped Holes Are a Late Sign of Emerald Ash Borer
Ash borer treatmentA D-shaped hole is not the beetle arriving. It is the beetle leaving. An egg was laid on that bark, the larva chewed into the living tissue just under the surface and spent a year or more winding through the plumbing that carries food from leaves to roots. Only then does an adult cut its way out. The first hole you see is a receipt for damage already done.
That lag is what makes this insect so good at killing quietly. For two years an infested ash looks fine from a lawn chair. The earliest honest signs are subtle: a slightly open top, pale flecked patches where woodpeckers worked the upper limbs, shoots from the lower trunk. Read those and you get a real choice. Wait for exit holes and the choice is between an expensive treatment with mediocre odds and a removal.
The metro has already lost more than nine thousand ash, and the ones still standing were treated or got lucky. If you have a large healthy ash shading the house, a two-year injection cycle is a good investment. If you have a mediocre ash at the back of the lot, we will tell you to take it out rather than sell you a plan that outlives your interest in it.
