The emerald ash borer has worked its way onto Xavier’s campus in recent years, infecting many trees and threatening others. Grounds foreman Walt Bonvell initiated a treatment regimen last year, injecting 13 trees with an insecticide, and expanded the program to include a total of 42 trees this year.
The insecticide, emamectin benzoate, was injected into the trunk of each tree between April and June. The solution works by killing the critter’s larvae during the stage of development that causes the most damage to the tree. Eggs are laid into the bark and develop into larvae that burrow into and eat the pulp, disrupting the flow of water and nutrients to the tops of the trees.
“Within one to three years, the tree just dies because they can’t take up any more water and nutrients, and it starts dying at the top where the new growth usually is,” Bonvell said.
There are nine emerald ash trees on the campus greenspace that were planted about 10 years ago when the new Gallagher Student Center was completed. They were among the trees treated this year, Bonvell said.
“Overall we have treated about 42 trees on campus, but we have many more, maybe about 100 or more scattered throughout Cohen, the Cintas area, the residential mall by Buenger, the west side by the south lot,” he said. “We pick the healthier trees that we feel we have a chance of saving. We can only afford to do so many. Every time I drive around campus, I see ash trees we haven’t done.”
His crews have had to take down three ash trees already, and he expects to have to remove more as the pest makes its way across campus.
“They were already half dead, and if you’re at a point when either a fourth or half of the tree is dead, then there’s no point in saving it,” Bonvell said. “We started seeing the borer in 2010. You could tell because once the canopy starts thinning out, you look for the D-shaped hole in the canopy.”
He said a few trees around the entrance to the O’Connor Sports Center appear to be infested, and he expects they’ll have to come down. “I hate taking down trees, but if that’s what it means to save another 40 trees, then that’s what we’ll do.”
The ash tree is a popular American shade tree planted in neighborhoods across the country, but many streets have lost all their trees because of the ash borer. The emerald-colored beetle is a foreign invasive species accidentally introduced from Asia into the U.S. in the 1990s. It was first confirmed in Michigan in 2002 and has spread to 14 states, including Ohio, and Canada and has killed more than 60 million ash trees nationwide.
Researchers have identified several natural parasites that have been released in Ohio and other Great Lakes states, according to the Michigan State University Knight Center for Environmental Journalism. Michigan State researchers have also had very positive results with the emamectin benzoate-based insecticide used at Xavier.