MARSHALL — It was bad news for ash trees in Lyon County — earlier this month, the Minnesota Department of Agriculture confirmed that emerald ash borer had been found in Marshall.

On Wednesday, representatives from the MDA encouraged Lyon County residents to keep an eye out for the destructive insects, and take steps to remove or treat affected trees.

“It’s important to be proactive,” said Jonathan Osthus of the MDA’s plant protection division. In many communities, ash trees make up about 20% of all trees in the city, Osthus said.

Around 40 people participated in a virtual information meeting on the emerald ash borer that was hosted by MDA representatives Wednesday afternoon. Osthus took questions from the audience, and talked more in-depth about emerald ash borer damage and precautions.

The virtual meeting is still available to watch at the MDA’s emerald ash borer website, https://www.mda.state.mn.us/eab.

The emerald ash borer is a small green beetle native to northeast Asia, whose larvae burrow under the bark of ash trees. The ash borers were first identified in the U.S. in 2002, Osthus said. However, he said it’s likely they arrived sometime in the mid-1990s, by hitching a ride in wood packaging.

The ash borers are now present in 37 U.S. states and five Canadian provinces, Osthus said.

“It’s causing widespread devastation,” he said.

Osthus said adult ash borers are usually active May through September. The adults lay their eggs in the branches of ash trees, and the larvae burrow under the bark. These burrows damage the tree’s ability to get water and nutrients. Over the course of five or six years, the ash borers multiply until the larvae’s tunnels girdle the host tree and kill it, Osthus said.

Osthus said the population of ash borers tends to grow slowly at first, and then faster over time.

“Then, a few years after that, you start to see a large number of trees dying in a short amount of time,” he said.

Osthus said some of the symptoms of an ash tree affected by emerald ash borer include a thinning tree canopy, bark splits and lots of shallow woodpecker holes on the tree.

“Woodpeckers love to feed on the insect larvae,” he said.

The holes woodpeckers make when feeding on ash borer larvae are oval-shaped and about the size of a dime.

Osthus said other signs of emerald ash borer include S-shaped tunnels under the tree bark, and D-shaped exit holes in the bark.

Osthus encouraged area residents to let the MDA know if they have found emerald ash borer.

“The best thing you can do is take a picture of the damage that you’re seeing,” he said. “If you see an insect gallery (tunnel), an adult beetle or a larva, take a picture of that or collect it.”

He recommended that evidence of emerald ash borer in a new location be reported to city staff by using the EDDMapS invasive species tracking app, or by contacting the MDA’s Report A Pest service.

If an ash tree is only lightly infected, or healthy and within about 10 miles of a known infestation, it’s possible to treat the tree with insecticide, Osthus said. The treatments are effective at protecting ash trees, but the treatments need to be repeated every couple of years for the rest of the tree’s life, he said.

“If you’re not going to treat the tree, it’s best to remove it,” Osthus said.

Trees affected by emerald ash borer should be removed between October and April, when the adult beetles are still dormant, he said.

When ash trees die, they can quickly become a hazard, “So you want to deal with the trees before they’re completely dead,” Osthus said.

Osthus said the MDA has a registry of licensed pesticide applicators that the public can search. However, the applicators on the registry don’t all necessarily provide treatments for emerald ash borer. The website www.treesaregood.org can also help members of the public find an arborist in their area, he said.

Another aspect of managing emerald ash borer is preventing the beetles’ spread to new places. Danielle DeVito of the MDA said Lyon County is under a quarantine which restricts the movement of items like firewood out of the county.

The MDA regulates ash wood, ash tree parts, mulch, and all hardwood firewood less than four feet long, DeVito said. Those items can’t be brought outside the ash borer quarantine area without a compliance agreement from the MDA, she said. Additionally, firewood can’t come into Minnesota from Canada or from other U.S. states without MDA certification.