Time Is Running Out to Treat Ash Trees

Northeastern Wisconsin forestry experts predict that emerald ash borers will kill more than 90% of all the large ash trees in Door County during the next few years, but property owners still may be able to save some prized trees.

Tree owners need to start planning this winter if they want to take action, said Bill McNee, the Department of Natural Resources’ (DNR) forest-health expert for eastern Wisconsin counties spanning from Kenosha to Door.

McNee said property owners should remember which trees seemed to be in poor health last summer and watch for bark damage this winter as woodpeckers look for easy meals in badly infested trees.

“I encourage the property owners to look at their ash trees this winter,” he said. “If they’re not too heavily woodpecker damaged, it still may be biologically timely to start treatments this coming spring.”

His advice came with one caveat, however: “You’re not going to have too much more time,” he said.

McNee suggests that anyone who has particular ash trees they want to save should call an arborist at a local tree service or nursery for a professional opinion.

“We encourage property owners to look at not just the financial cost, but what benefits do these trees bring you in terms of the view, the shade, helping keep your property values up, the nice fall color and reducing your air-conditioning use?” McNee said. “The answer may not be so simple as, ‘Here’s what I was going to pay for treatment.’”

He also said owners cannot treat a tree for just one year, then skip two years and expect it to survive. Left untreated, emerald ash borer infestation is “more than 99% lethal” to larger ash trees. That means people must take a hard look at their budgets and values.

“Some property owners may look at those 10 trees and go, ‘I’m looking at a $2,000 bill every year for the next 20 years. That doesn’t make sense. I can buy a new Lexus for that kind of money,’” McNee said.

There are options, however. It doesn’t have to be an all-or-nothing approach.

“Some may pick the nicest one that’s the healthiest and treat that one, and the others get removed and replaced with other species,” he said. “Other property owners I know will spend whatever it takes: They want the ash trees and that nice canopy cover, and cost is secondary.”

Emerald ash borers don’t have much effect on immature trees, but they seem to start damaging Door County ash trees when their trunks have grown larger than four inches in diameter, according to DNR foresters Jake Schroeder and Chris Plzak. Schroeder just left Door County for a position in Waupaca, and Plzak is covering the county until the DNR finds Schroeder’s replacement. Earlier in his career, Plzak served for 16 years as Door County’s forest-health specialist.

Both Plzak and Schroeder say ash trees won’t become extinct. They’ll continue to propagate and then become infested and die before becoming large trees.

McNee said it’s possible for property owners to start treating smaller ash trees themselves, though results vary. For larger trees, approaching 12 inches in diameter, he recommends having a professional do the treatments to ensure better distribution of the insecticide in the tree. Some arborists drill into the tree to inject pesticide directly into the tree’s water system. Others push a big needle into the soil a foot or so under the base of the tree to inject pesticide there, and the tree absorbs it.

“The general rule of thumb is you can probably treat your tree for a decade and spend less money than you would spend to remove and replace it,” McNee said, “and in 10 years, you get to have this nice, big tree, and it helps keep your property values up.”