Emerald Ash Borer: Treat or Remove Your Ash Tree?

Treat your ash if it's healthy or has lost less than half its canopy, it's in a spot where you want a big shade tree, and you're willing to keep treating it for as long as you own it. Remove it if more than half the crown is thin or dead, if it has trunk or structural damage, or if it's a tree you wouldn't miss. University extension guidance draws the line at 50% canopy thinning. Above that, insecticides rarely bring the tree back.

On a golf course we sorted our ash the same way: keep the ones that frame a hole or shade a tee, and take out the rest before they died and turned into a liability. You can do the same in your yard.

First, confirm it's ash and it's EAB

Emerald ash borer only attacks true ash (Fraxinus). Mountain ash isn't a true ash and isn't affected. Ash leaves are compound with 5 to 11 leaflets, and they grow opposite each other on the twig. Mature trees have tight, diamond-patterned bark.

Look for at least two of these, because any single symptom can come from another pest or stress:

• D-shaped exit holes about 1/8 inch across, with clean edges, where adults chewed out
• S-shaped tunnels packed with fine sawdust under loose or split bark
• Heavy woodpecker work that strips the outer bark and leaves pale patches ("blonding")
• Thinning from the top down, with dead branch tips high in the crown
• Sprouts coming out of the trunk or big limbs low on the tree

The beetle is now in dozens of states, from the East Coast across the Midwest to Colorado's Front Range and western Oregon. If your county has confirmed EAB, assume your untreated ash will get it.

Judge the canopy honestly

Stand back far enough to see the whole crown and compare it with a healthy ash, or with what the tree looked like a few years ago. Picture the crown in quarters. If two of those quarters are bare or full of thin, tufted leaves only at the branch ends, you're at 50% and the tree is a removal.

Ash is one of the first trees to drop its leaves in fall, so in October you may be looking at bare branches. If you can't tell, mark your calendar for June, when the tree is fully leafed out. That's also right in the best treatment window, so you lose nothing by waiting.

Trees under about 30% dieback are the strongest treatment candidates. Between 30% and 50% it's a judgment call, and treatment works best on trees that are still growing well.

The treatment options

Every systemic treatment has to be repeated for as long as you want to keep the tree. You're not curing it, you're keeping it protected.

Emamectin benzoate trunk injection (arborist only). This one has the best research behind it. In trials, a single injection gave close to complete larval control for 2 to 3 years, so most arborists treat every other year. The best time is after the tree leafs out in spring, roughly mid-May to mid-June. Your arborist drills small holes around the base of the trunk and injects through them.

Imidacloprid soil drench (homeowner products). This is what you'll find at the hardware store, under labels like BioAdvanced 12 Month, Bonide Annual and Ferti-lome. You mix it with water and pour it around the base of the trunk. It has to be done every year, and spring works best. Wisconsin Extension recommends mid-April to mid-May. A fall drench can work, but research shows it takes higher rates to get the same control, and you can't go over the rate on the label.

The size limit matters. Homeowner drenches work on trees under about 15 inches in diameter, which is about 47 inches around at chest height. On bigger trees they don't deliver enough insecticide, and labels cap how much you can legally apply per acre per year. If your tree is bigger than that, hire an arborist.

To measure: wrap a tape around the trunk 4.5 feet off the ground and divide by 3.14. A 63-inch circumference is a 20-inch tree, which is arborist territory.

Check your state's rules too. A few states restrict certain products or require a licensed applicator for some methods.

What each choice costs

These are rough figures as of October 2026. Get local quotes.

• DIY drench: about $20 to $50 a year for a small tree
• Arborist injection: about $7 to $16 per inch of diameter per two-year treatment, and often $200 or more per visit. A 20-inch tree at $12 an inch is about $240 every other year.
• Removal: about $500 to $1,200 for a 30 to 50 foot tree, and $1,100 to $2,200 for a 50 to 70 foot tree. Stump grinding is extra, usually $100 to $400.
• Dead ash removal: usually 25% to 50% more than a live tree of the same size

The last number is the one that catches people. Dead ash goes brittle fast. Climbers won't go up a tree they don't trust, so the crew brings in a bucket truck or crane. And a brittle limb over your roof, driveway or the kids' swing set is a hazard every windy day until it's down.

Run the numbers for your own tree. A healthy 20-inch ash shading the south side of your house costs about $2,400 to treat over 20 years. Removing it, grinding the stump and replanting can cost close to that up front, and you'd wait 20 years or more for that much shade again. For a tree like that, treating is the better deal. For a scraggly ash in the back corner, it isn't.

If you remove it

• Don't wait for it to die. A live tree is cheaper and safer to drop.
• Winter works well. On frozen ground, the trucks and log loads leave fewer ruts in your lawn.
• Don't move the wood. Keep the firewood local or have the crew chip it. Hauling ash firewood is how the beetle got around the country.
• Replant with something else. Fall is a good time for that up north (see planting trees in fall). Pick a different genus than your neighbors have, so the next pest can't wipe out the whole street at once.
• Grind the stump or keep cutting the sprouts. Ash suckers hard after it's cut.

If you treat it

• Book the arborist now for a May or June injection. The good companies fill their spring schedules early.
• Water it going into winter if fall has been dry. A tree under drought stress takes up systemic insecticide poorly. Here's how to water trees before the ground freezes.
• Don't prune dead ash wood high in the crown yourself. Brittle ash limbs drop without warning. Small, low deadwood is fine. See fall pruning: what to cut now.
• Keep treating even after most of the ash around you is gone. Ash seedlings keep coming up, and they keep the beetle around.

The decision in one pass

1. Confirm it's a true ash and you see at least two EAB signs, or EAB is confirmed in your county.
2. Look at the canopy. More than 50% thin means remove. Under 30% means treat if you value the tree.
3. Measure the trunk. Under 15 inches across, you can drench it yourself each spring. Over 15 inches, hire an arborist for injections every two years.
4. Ask whether you'd replant a tree in that spot. If not, take it out while it's still alive and cheaper to drop.

Related: Deer Damage to Shrubs in Winter: Prevention That Works · Salt-Tolerant Shrubs and Grasses for Curb Strips and Driveways

Sources (6)

• University of Minnesota Extension: Emerald ash borer
• Wisconsin Horticulture: Homeowner guide to emerald ash borer insecticide treatments
• Wisconsin Horticulture: Is my ash tree worth treating?
• Michigan State University: Multi-year protection of ash trees with one trunk injection of emamectin benzoate
• Colorado State University Extension: Insecticides used to control emerald ash borer on residential shade trees
• Wisconsin DNR: Signs of emerald ash borer

Photo: Plant Protection and Quarantine (34954841290).jpg) by APHIS.gov, Public domain.