Can My Ash Tree be Saved?
Kevin O’Connor calls on an entomologist to tackle the problems posed by the emerald ash borer
We have a beautiful, healthy ash tree that is 36 years old and about 50 feet tall. But we’re worried about what’s going to happen to it now that emerald ash borers have been discovered nearby. What can we do to prevent borers from killing our tree?
—Vicky Osterholt, Springfield, IL
This invasive beetle, which got its first toehold in North America in Detroit in the 1990s, has spread like wildfire throughout the eastern half of the U.S. and Canada, leaving millions of dead ash trees in its wake. I took your question to Daniel Herms, a professor of entomology at Ohio State University, who has been studying the effectiveness of different control measures on this pest. Here’s what he has to say.
“The emerald ash borer (EAB) is most damaging during its larval stage, when it tunnels beneath the bark and dines on the tree’s juicy vascular tissue that delivers water, minerals, and nutrients to the rest of the tree. If the larvae eat the tissue all around the tree, then it’s girdled and slowly dies.
“It’s tough to know if EAB larvae are under the bark, so if borers are known to be within 10 to 15 miles of an ash tree, it makes sense to treat it with a systemic insecticide. A systemic makes the entire tree toxic to the larvae and the adults, but it works only if the vascular tissue is functioning and able to carry the insecticide throughout your tree.
“Our studies have shown very good results when the trunks of large trees like yours are injected with an insecticide containing emamectin benzoate between mid-May and mid-June, after the trees flower and leaf out. One treatment by a licensed professional provides two years of protection. Our studies have also shown that drenching the soil with imidacloprid is very effective on trees with trunks up to about 20 inches in diameter. Home-owners can apply insecticidal drenches, but they must be ad-ministered every spring, and only after the tree has flowered and just as leaves are beginning to form.
“If you keep up the treatments, there’s an excellent chance your tree will continue to flourish, even if others nearby are infested with borers. But once a tree has lost more than 50 percent of its crown, it’s too late for insecticides to help.”
To learn more about the spread and control of EAB, go to the Emerald Ash Borer Information Network.
Shown: Adult emerald ash borers chew D-shaped holes through the bark when they emerge from white ash trees around the middle of June.