Getting rid of emerald ash borer (EAB) requires either treating your ash trees with systemic insecticides or removing heavily damaged trees entirely. Eradication isn’t realistic once these beetles are established in an area, but you can protect individual trees and stop the damage from progressing. The key factor is how far the infestation has advanced: trees with less than 30% canopy thinning are good candidates for treatment, while trees beyond that point are generally too far gone to save.
Spotting an Infestation Early
EAB damage starts hidden under the bark and works its way outward, so by the time you notice obvious decline, the beetles may have been feeding for a year or more. The earliest visible symptom is thinning leaves at the top of the tree, which typically appears within one to three years of infestation. This happens because the larvae feed just under the bark, disrupting the flow of water and nutrients to the upper canopy.
Look for these signs, roughly in order of how they appear:
- Crown dieback: Leaves thin out starting at the top of the tree, then individual branches die.
- Epicormic sprouting: New shoots sprout from the trunk or base of the tree, often just below where larvae are feeding. This is the tree’s attempt to grow wherever it still can.
- D-shaped exit holes: Roughly 1/8 inch in diameter, these are where adult beetles emerged from under the bark. The distinctive D shape separates EAB from other wood borers, which leave round holes.
- Bark splits: Vertical cracks in the bark caused by the tree forming callus tissue around larval tunnels. Peel back the bark at a split and you’ll often see S-shaped galleries packed with sawdust-like material.
- Woodpecker damage: Increased woodpecker activity, especially higher up the trunk, is a reliable clue. They strip away outer bark to reach larvae underneath, creating a “flecked” appearance that may eventually extend down the entire trunk.
Decide Whether Your Tree Can Be Saved
Before spending money on treatment, assess how much canopy your tree has lost. Research has shown that insecticides can protect trees even after canopy density has dropped by 50%, but in practice, most arborists won’t recommend treating a tree that’s lost more than 30% of its canopy. Beyond that threshold, the tree has likely suffered structural damage that won’t recover even if the beetles are killed. The remaining branches become brittle and prone to breaking, and the tree’s appearance won’t meaningfully bounce back.
If your tree still has a full or mostly full canopy, treatment is well worth considering. Healthy, well-maintained ash trees can be protected for years with ongoing insecticide applications. If the canopy is severely thinned, removal is the safer and more cost-effective choice.
Chemical Treatment Options
Four active ingredients are used against EAB, and they differ in how they’re applied, who can apply them, and how well they work.
Trunk Injection (Professional Only)
The most effective option is a trunk injection of emamectin benzoate. A licensed arborist uses specialized equipment to inject the insecticide directly into the tree’s vascular system, where it spreads throughout the canopy and kills larvae feeding under the bark. This treatment lasts two to three years per application, making it the most convenient long-term option. It can be applied anytime from April through September, though spring applications tend to produce the best results.
A neem-derived compound called azadirachtin is another trunk-injection option. It’s a natural-sourced insecticide extracted from neem tree seeds, but like emamectin benzoate, it requires professional application and specialized equipment.
Soil Drench (DIY Possible)
Imidacloprid is the most common homeowner-applied treatment. You mix it with several gallons of water and pour it onto the soil around the base of the trunk. The tree’s roots absorb the insecticide and carry it up into the canopy. If you have mulch around the tree, remove it before applying. The best timing is mid-April to mid-May, though a fall application window (early September to mid-October) is also listed on some product labels.
There’s an important size limit for DIY treatment: soil drenches are only effective on trees with a trunk diameter of 15 inches or less (about 45 inches in circumference). Larger trees need professional treatment because a soil drench can’t move enough insecticide into a big canopy to provide adequate protection.
Trunk Spray
Dinotefuran can be sprayed directly onto the bark, where it penetrates and moves through the tree more readily than other EAB insecticides. This is applied in late April to late May. It can also be applied as a soil drench, but that method is more expensive without improving results.
When and How Often to Treat
Spring applications are more effective than fall applications at controlling EAB and protecting canopy health. The goal is to have the insecticide distributed throughout the tree before adult beetles emerge and larvae begin feeding. For most treatments, this means applying between mid-April and late May, depending on your climate and the product you’re using.
Treatment is not a one-time fix. Soil drenches with imidacloprid need to be reapplied every year. Trunk injections with emamectin benzoate last longer, typically two to three years between treatments. As long as EAB is present in your area, you’ll need to continue treating your ash trees indefinitely. Stopping treatment leaves the tree vulnerable again.
Removing a Heavily Infested Tree
If your tree has lost more than 30% of its canopy, removal is the practical choice. Heavily infested ash trees become structurally compromised as larvae destroy the tissue layer that transports nutrients. Dead branches high in the canopy can fall unpredictably, creating a safety hazard.
Hire a professional for removal, especially for large trees near structures or power lines. Infested wood doesn’t need special disposal in most cases, but you should never transport ash firewood to a new area. Moving firewood is one of the primary ways EAB spreads to uninfested regions. Many states and counties have quarantine regulations that restrict the movement of hardwood firewood. Use the wood locally, chip it, or have it hauled away by your tree service.
Biological Control: A Long-Term Approach
Eradicating EAB from a region isn’t feasible, but biological control programs aim to keep populations low enough that ash trees can survive. The USDA has introduced three species of tiny parasitoid wasps from the beetle’s native range in Asia. Two species attack EAB larvae under the bark, and a third destroys EAB eggs found in bark crevices. These wasps are about the size of gnats and pose no risk to people or other species.
Biological control is a community-scale strategy, not something individual homeowners deploy. The wasps are reared at a federal facility in Michigan and distributed to states with EAB infestations. The goal is for these natural enemies to establish self-sustaining populations that continuously suppress EAB numbers over time. This won’t save a tree that’s already heavily infested, but it may reduce the pressure on treated trees and slow the spread across a landscape.
Protecting Uninfested Ash Trees
If EAB has been confirmed in your county but your ash trees still look healthy, preventive treatment is worthwhile. Trees respond far better to treatment before they’re damaged than after. A soil drench applied in spring to a healthy tree under 15 inches in diameter is a straightforward, relatively affordable way to stay ahead of the problem. For larger or high-value trees, scheduling a professional trunk injection with emamectin benzoate every two to three years provides the strongest protection available.
Keeping your ash trees healthy through proper watering and avoiding root damage also matters. Stressed trees are more attractive to EAB and less able to tolerate feeding damage. A well-maintained tree combined with timely insecticide treatment gives you the best chance of keeping your ash trees alive through an EAB infestation.