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If you have an ash tree in Indiana, the emerald ash borer has probably already found it, or it will. Purdue says this small green beetle will kill every ash tree that isn’t protected with insecticide. So the real question isn’t whether to do something. It’s whether your tree is worth saving.
This guide walks you through it in six steps: confirm it’s really an ash, check for signs of the beetle, use the 30% canopy rule, pick a treatment, compare costs, and remove the tree safely if that’s the right call.
What’s in This Guide
Step 1: Make Sure It’s an Ash Tree
Emerald ash borer only attacks true ash trees, so start here. North Dakota State University lists the features that give an ash tree away: Source: NDSU Agriculture — Ash Tree Identification
- Opposite branches. Buds and branches grow directly across from each other, not staggered. A few may be missing where branches died.
- Compound leaves with 5 to 11 leaflets, arranged in pairs with one leaflet at the tip.
- Bark with diamond-shaped ridges on older trees. Young bark is smoother.
- Seeds with a single long wing, hanging in clusters that can stay on into winter.
Common look-alikes
NDSU points out a few trees people mix up with ash:
- Boxelder has opposite, compound leaves too, but only 3 to 5 leaflets, and its seeds come in pairs.
- Black walnut has 9 to 15 leaflets, but they alternate along the stem instead of growing in pairs.
- Mountain-ash isn’t a true ash at all. It has alternate leaves and red-orange berries, and emerald ash borer doesn’t attack it.
Step 2: Look for Signs of Emerald Ash Borer
The adult beetle is bright metallic green and about a third of an inch long, according to Purdue. You’ll rarely see one. The damage is done by the larvae feeding under the bark, so you have to read the tree instead. Source: Purdue University — Emerald Ash Borer
University of Minnesota Extension lists the signs to look for: Source: University of Minnesota Extension — Emerald Ash Borer
- Thinning at the top of the tree. Dieback in the upper canopy is usually the first thing you’ll notice.
- “Blonding.” Woodpeckers strip off the outer bark to get at the larvae, leaving pale, light-colored patches on the trunk and branches.
- D-shaped exit holes. Adult beetles chew small holes, about 1/8 inch across, with one flat side, as they leave the tree.
- Vertical bark splits where the tree is trying to heal over the tunnels underneath.
- S-shaped tunnels under any loose or split bark.
- Sprouts (called epicormic shoots) growing out of the trunk or the base of the tree.
One sign by itself doesn’t prove the tree is infested. Sprouts and bark cracks can have other causes. But two or three of these together on an ash tree is a strong clue. A pair of binoculars makes it much easier to check the top of the canopy and the upper branches for blonding.
Step 3: Check the Canopy (the 30% Rule)
This is the step that decides it. Purdue says trees that have lost more than 30% of their canopy shouldn’t be treated, because too much of the tree is already dead. Source: Purdue Entomology — Emerald Ash Borer Management
A Purdue study summarized in the Purdue Landscape Report found that trees with about 10% canopy loss usually respond well to treatment. Once a tree reaches 30% loss, saving it rarely works. Source: Purdue Landscape Report — Revisiting Ash Tree Protection
Stand back where you can see the whole crown, ideally in summer when the leaves are on, and estimate how much of it is bare or thin. Here’s how to use what you see:
- Full, healthy canopy: a good candidate to treat.
- Some thinning at the very top, under 30%: still worth treating, the sooner the better.
- More than 30% thin or dead: plan to remove it.
Other states use a looser cutoff. Minnesota and Nebraska put it at about half the canopy. For an Indiana ash tree, Purdue’s 30% rule is the one to follow.
Location matters too
Purdue also says to remove ash trees that will run into power lines or buildings as they grow, and to save the ones that have room to thrive. A healthy ash tree shading the south side of your house is worth more than one crowding the wires.
Step 4: Choose a Treatment
Treatment doesn’t wipe out the beetle. It protects a healthy tree, and it has to be repeated for as long as you want to keep the tree. The Nebraska Forest Service says ash trees that are saved will likely need treatment for the rest of their lives. Source: Nebraska Forest Service — Homeowner Guidelines for Emerald Ash Borer
Do-it-yourself soil treatments
Garden centers sell ash tree treatments that you pour into the soil around the base of the tree. University of Minnesota Extension says homeowners should only treat trees smaller than 15 inches in diameter themselves. Anything bigger should be treated by a professional arborist.
To check your tree, measure around the trunk about 4½ feet off the ground with a flexible soft tape measure and divide by 3.14. A trunk that measures 47 inches around is about 15 inches across.
Minnesota Extension also notes that these garden-center products contain neonicotinoids, which are highly toxic to bees and butterflies. Follow the label exactly, and don’t use them near flowering plants.
Professional trunk injections
For bigger trees, an arborist can inject an insecticide called emamectin benzoate directly into the trunk. Purdue’s long-term study found this gave the best, longest-lasting protection, and that treating once every three years was enough to protect the tree. Minnesota Extension puts the interval at every two to three years.
The same study found that skipping treatments catches up with you. Damage increased 4 to 5 years after the last treatment, and by 6 years some trees had declined to the point of needing removal.
Step 5: Compare the Cost of Treating vs. Removing
Purdue’s study estimated about $300 per professional treatment. On a three-year schedule, that works out to roughly $100 a year. Removing a large ash tree was estimated at $1,800 to $3,600, depending on the tree and where it is.
Purdue’s conclusion is that keeping up regular treatment on trees that can be saved is the most cost-effective option. Protecting a large tree usually costs less than removing it and keeps your shade. Just remember to count the hidden costs of removal too: a replacement tree, and years of waiting for it to grow.
Prices vary a lot by tree size and company, so get a written quote from a certified arborist for both options.
Step 6: If You Remove It, Do It Safely
If your ash tree is past the 30% mark, don’t wait. Purdue warns that dead and dying ash trees can be dangerous when they fall on people and property. Minnesota Extension adds that dead ash branches turn brittle, so removing a tree while it’s still alive is cheaper and easier than removing a dead one.
A few more rules for removal:
- Hire a pro for anything big or near the house, driveway, or power lines. A brittle ash can break in ways you don’t expect.
- Minnesota Extension says the best time to remove an infested ash is November through April, when the beetles aren’t flying.
- Don’t move the wood. Purdue says the beetle spreads when infested ash firewood and logs are moved, so burn it at home or let the tree company take it, and buy firewood where you’ll burn it.
Once the stump is gone, plan a replacement. Pick a tree other than ash, and give the new tree the care it needs to get through its first winters. Our guide to winter tree care covers the basics for young trees.
If you keep it
Purdue recommends taking off dead limbs on treated ash trees, since they won’t recover and can fall. Late winter is the best time for most pruning. Here’s when to prune trees in Indiana, tree by tree.
Frequently Asked Questions
Can an ash tree survive emerald ash borer without treatment?
Almost never. Purdue says the beetle will kill all ash trees that aren’t protected with insecticide. Untreated trees in Indiana should be expected to decline and die.
How do I know if it’s too late to save my ash tree?
Look at the canopy. Purdue says trees that have lost more than 30% of their canopy should not be treated. Trees with about 10% loss usually respond well.
How often does an ash tree need to be treated?
Professional trunk injections of emamectin benzoate are typically repeated every two to three years. Purdue’s study found once every three years gave enough protection. Treatment needs to continue for the life of the tree.
Can I treat my own ash tree?
Only if it’s small. University of Minnesota Extension says homeowners should only treat trees under 15 inches in diameter. Larger trees should be treated by a professional arborist.
Is a dead ash tree dangerous?
Yes. Dead ash wood becomes brittle, and Purdue warns that dead and dying ash trees can be dangerous when they fall on people and property. Have it removed by a professional as soon as you can.
Sources & Further Reading
- Source: Purdue Entomology — Emerald Ash Borer Management
- Source: Purdue Landscape Report — Revisiting Ash Tree Protection
- Source: Purdue University — Emerald Ash Borer
- Source: University of Minnesota Extension — Emerald Ash Borer
- Source: Nebraska Forest Service — Homeowner Guidelines for Emerald Ash Borer
- Source: NDSU Agriculture — Ash Tree Identification