Emerald Ash Borer Discovered in Superior, Wisconsin

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The emerald ash borer, an invasive insect species that has killed tens of millions of ash trees in the United States and Canada, has been found in Superior, the first infestation discovered on the western shores of Lake Superior.

Eastern shores of the Lake have already been dealing with the frighteningly fast-spreading pest, and specialists there bring a perspective on what the western portion of the Lake region now faces.

It was August 7 when a tree crew noted signs of an emerald ash borer infestation, including the characteristic D-shaped holes and tunneling beneath the bark, on a dead ash tree they were removing from Superior’s North End. They sent photos and an insect specimen to the U.S. Department of Agriculture and awaited the dreaded official confirmation, which came August 13. The city of Superior has some 3,000 ash trees on public boulevards and park lands.

“This infestation is really going to change the landscape,” Superior Mayor Bruce Hagen said Thursday in a statement.

In 2002, the half-inch beetles were discovered in southeast Michigan. Native to Asia, the insects likely hitched a ride to North America in untreated wood used as packing material. The emerald ash borer has since spread to more than a dozen states. Larvae eat away at the trees’ inner bark and destroy the connective tissues. Infested trees often die in just two or three years. Here, the species has no natural predators.

Along the shores of Lake Superior, the insects had already reached Michigan’s Upper Peninsula, including the Keweenaw, and the southeastern Ontario shore. But until now, they hadn’t been found in northern Wisconsin or, in Minnesota, north of the Twin Cities.

One Lake Superior-based company, BioForest Technologies in Sault Ste. Marie, Ontario, makes an injectable organic insecticide called TreeAzin from neem-tree seeds. Developed in partnership with the Canadian Forest Service, it’s been used to combat the ash borer in the United States and Canada, including by the city of Sault Ste. Marie. The insecticide works by disrupting larval molting, affecting adult insect fertility and inhibiting egg viability. In a continuing study of 400 trees treated since 2008, TreeAzin has been 98 percent effective.

Saving your trees

For homeowners hoping to save a few beloved shade trees, “You need to begin your treatments early,” says Joe Meating, BioForest’s president and the former insect control officer for the Canadian Forest Service.

“It’s far more effective if you’re treating trees that are relatively healthy. We’ve had people wait until they see physical symptoms, and then it’s very difficult to treat.”

Those symptoms can include D-shaped exit holes, increased woodpecker activity, a thinning crown, splitting bark, shoots growing from the trunk and S-shaped marks on the bark. Treatment is costly, but it can be cheaper than tree removal and replacement.

In woodlands thick with ash – and where treatments aren’t feasible – Joe says to expect severe damage. Opportunistic invasive plants could take over, and he worries about erosion, too.

“I don’t think we’ll ever really stop (the emerald ash borer),” he says. “I’ve been doing this for 40 years and never seen anything like it. Many insects focus on stressed or damaged trees. Emerald ash borer doesn’t care.”

But, he adds, “We can slow down the development in a municipality and keep many trees alive.”

Unaided, the species spreads just a few miles a year. A large leap – like this one to Superior – is almost always a human-caused phenomenon, the result of the inadvertent transportation of infested firewood or nursery stock. Many counties prohibit outside firewood for that reason.

Douglas County, like others with confirmed infestations, has been quarantined. Firewood and live trees cannot be moved out of the county; businesses that handle wood products must “ensure that their products are pest-free before shipping,” according to city officials.

Across the St. Louis River, Duluth Mayor Don Ness held a press conference to outline the city’s response. He says Parks and Forestry staff have already identified all 4,500 of Duluth’s boulevard ash trees and will continue to search for signs of infestation. The mayor says Duluth will work closely with the city of Superior to slow the emerald ash borer’s spread.

As the infestation continues to expand beyond quarantined zones, U.S. Forest Service officials are evaluating more aggressive options, like introducing stingless wasps, natural predators of the emerald ash borer.

“The more you look, the more you find,” says Joe. “Once the outbreak gets going, it progresses very, very rapidly. You don’t have time to waste.”