MANKATO — It’s too early for Mankatoans to be worrying about treating their ash trees with insecticide, according to the Minnesota Department of Agriculture.

It’s not too early to start planning — and maybe saving up some money — for the inevitable arrival of the emerald ash borer in the Mankato area.

The ag department recommends delaying treatment until the ash borer has been found within 15 miles of a particular property. At this point, the nearest locations where the ash-killing pest have been found are Prior Lake in Scott County and Welcome in Martin County — each about 46 miles from Mankato as the beetle flies.

“It’s just a matter of time,” said Dave Iveland of St. Clair-based Lawn Pro.

Because of Lawn Pro’s wide service area — stretching from Fairmont to Northfield and from Redwood Falls to Rochester — Iveland has already treated ash trees with the insecticide that can fend off emerald ash borer.

“I’ve witnessed it firsthand in Winona and Rochester,” he said.

He’s treated ash trees in the Fairmont-Welcome area and Rochester, where the beetles are already confirmed to be in the area. And he’s treated trees where the pests might still be miles and years away.

“I’ve done some in the Mankato area,” Iveland said.

The Department of Agriculture advice makes sense, as long as people are keeping a close eye on their ash trees. The treatments still work even after emerald ash borers have made a home in an ash tree, as long as they haven’t done too much damage, said Ashley Steevens, Mankato’s parks superintendent whose degree is in forestry.

“A tree that’s lightly infested can still be saved,” Steevens said.

But people shouldn’t assume they have plenty of time just because the nearest sightings of the insect are 46 miles away. Less than a year after they were found in Winona, they were discovered in Rochester — 45 miles away.

“It may be here already,” Iveland said. “You may not know it’s here until you start to see die-back on trees.”

The widespread impact — virtually the entire eastern half of the United States is infested and has now been joined by states like Texas and Colorado along with most of the Upper Midwest — has brought scads of information on the emerald ash borer to the internet. Sites can quickly be found to help people identify ash trees in their yard, learn to differentiate the ash borer from other beetles and spot evidence of an infestation on trees.

Beyond educating themselves, owners of ash trees would be wise to start thinking about what their strategy will be when the infestation makes its way to their property.

The treatments work, but they’re not a one-time deal. The cheaper option — injecting a chemical in the soil around the tree — is less expensive but needs to be repeated annually. Lawn Pro charges $3-5 per inch of tree-diameter (measured at chest height) for each soil injection.

An even more effective treatment involves injecting a different insecticide beneath the bark of ash trees. Following the manufacturer’s advice, the trunk-injection method lasts for two years. There’s some evidence it might even work for three years.

But the cost is $7-10 per inch of diameter and the price rises beyond that ratio for the largest trees — those thicker than 20 inches.

So homeowners could spend hundreds, even thousands, of dollars keeping a large ash tree safe from EAB for 10 or 20 years.

The alternative — cutting the tree down — isn’t cheap either, especially if it’s a towering ash or one in a backyard or other location that’s hard to reach.

A tree near the street could be removed for a few hundred dollars. A more time-consuming job could push the cost well beyond $1,000, said Iveland, who knows one tree-removal specialist who charges about $3,500 a day.

Letting nature take its course could be even more expensive in the long run.

Ash trees tend to die quickly when the EAB population soars in an area, and they can’t be safely left in their deceased condition. Ash trees typically begin to drop branches — even large limbs — as soon as one year after they die.

So failing to act could bring legal liability if a neighbor is injured or a neighbor’s property is damaged by falling limbs. Cities can also condemn a tree and order its removal.

And if people wait to act until the infestation is peaking, they may struggle to find crews available to remove a dead or dying tree.

“Once it gets into an area, then everybody gets busy and they’re not available,” Iveland said of tree-removal companies.

As for people who are relying on that cold snap last winter — with temperatures reaching -29 in south-central Minnesota — to have wiped out all of the emerald ash borers, keep dreaming.

“It doesn’t eliminate it,” Iveland said. “It just slows it down a bit.”

One potentially not-quite-so-expensive option is to get rid of ash trees soon — picking a time of the year when a tree service is looking for work. That might be the wisest choice for a small ash tree, a larger tree that’s not particularly healthy, or one that’s not greatly valued aesthetically or for the shade it provides, Steevens said.

“Work through the options before it’s at our door,” she said.

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