How to Protect and Save Your Trees from Emerald Ash Borer

Kristen Schmidt

If, like many homeowners, you have ash trees on your property, emerald ash borer is a constant threat-if it hasn't already infested some of your trees. The invasive beetle species has already killed tens of millions of trees across the East Coast. But arborists and researchers are increasingly encouraging property owners to treat diseased ash trees, rather than defaulting to removal. It's not a false promise, either; research is showing the lives of some ash trees can be prolonged for years if they're treated well and consistently.

"You can protect and save trees," says Amy Stone, a horticulturist and educator with the Ohio State University Extension who is credited with the 2003 discovery of emerald ash borer in Ohio. "There are many people who have thought that, by treating, you're just prolonging the life of the tree and it will die, but that's not the case. If you continue down that road of treatment, you can keep a tree alive for an indefinite number of years."

Emamectin benzoate is one of the newer and more effective treatments for emerald ash borer infestation. "It has to be applied by someone who's licensed, but it will give multiple years of control," Stone says. The tool of choice for application is trunk injections, but arborists can also choose to spray bark or inject insecticide into the ground near the roots, she says. A licensed, trained arborist is the best person to assess the health of ash trees and to offer homeowners realistic options, she adds.

Other insecticides are commercially available to homeowners and can easily be mixed with water and applied to the ground at the roots of an at-risk tree. "If you have a tree with 15 inches or below diameter, homeowners can have relatively positive experiences treating that tree. As you get into larger trees, you may want to engage with an arborist."

The decision to treat or remove, though, is personal. Money factors in-removing multiple trees at once could cost thousands of dollars-and so do curb appeal and aesthetics. If a homeowner has 10 ash trees, for example, he may treat some and remove others to spread out the removal cost. "Or they may treat all the trees for the rest of their lives as a means to protect and have those ash trees around," Stone says.

On the horizon: Researchers with the National Forest Service are studying "lingering ash," trees that are staying alive when other ash trees around them have died. They might have a biological resistance to emerald ash borers, and if that can be studied and understood, it could someday be bred into resistant ash trees.

Replacing an Ash Tree

If you choose to replace dying or dead ash trees, experts recommend making a choice that will increase the species diversity on your property. Amy Stone of the Ohio State University Extension offers these suggestions. Visit for recommendations based on terrain, light and other factors.