Emerald ash borer, the invasive insect that threatens million of acres of Minnesota ash forest and tens of thousands of boulevard trees, has been confirmed in Duluth for the first time.

The invasive beetles were found in the larval stage in four of 35 ash trees inspected on Park Point.

It’s the first confirmed Minnesota infestation of the emerald ash borer north of the Twin Cities area, but was not unexpected, with the critter already devastating ash trees in Superior for at least the past two years.

The Minnesota Department of Agriculture and city officials announced the discovery Friday.

“Park Point isn’t very far across the bay from Superior… one of them could have easily flown across there,” said Kelly Fleissner, City of Duluth manager of maintenance operations.

The bug was found as part of a three-year study testing different methods for finding the species, including removing branches from ash trees to peel back the bark and look for signs of the insect.

“This area has been a focus of ours for several years, ever since the discovery of EAB just across the border in Superior” in August 2013, said Mark Abrahamson, entomologist for the Minnesota Department of Agriculture. “Now that we have found the insect, we can work with our partners in the city of Duluth and St. Louis County, and residents and businesses to take measures to slow its spread in the northern part of the state.”

Specimens have been sent to the U.S. Department of Agriculture for confirmation, which is expected within days.

State agriculture inspectors placed an immediate emergency quarantine on Park Point limiting the movement of any hardwood firewood, ash trees, debris or limbs or wood of ash trees from leaving the peninsula. Similar, permanent quarantines already have been put into effect in 11 southern Minnesota counties since the bug was first confirmed in the state in 2009.

The bug’s larvae kill ash trees by tunneling under the bark and feeding on the part of the tree that moves nutrients up and down the trunk.

City plan in effect

Duluth has about 4,500 mostly green ash just on boulevards - nearly one in five of the trees along city streets - and thousands more ash trees in urban forests across the city.

City officials on Friday said that, anticipating the invasion, they already have started a emerald ash borer action plan that includes chemical injections for about 1,000 “high-value” boulevard and park trees larger than 12 inches in diameter. Those injections cost about $70 but last two years and have proven effective in places such as Milwaukee at preventing ash from succumbing to the borer.

All of the city’s boulevard and park ash trees under 12 inches in diameter will be cut down, whether they have the bug or not, Fleissner said.

“We’re going to start around Park Point and work out from there,’’ he added, noting it will take several years. “The goal is to get out ahead of it before it spreads. Then we can save a few more trees and it will cost us less.”

For trees on private property, Fleissner said homeowners now have a decision to make.

“If they consider it a high-value ash tree, they need to call one of the local (tree service) businesses that does injections. Otherwise, they should cut it down and get rid of it,” he said.

Any ash cut on Park Point, even if it is chipped, will have to stay there until winter, Fleissner noted. Eventually it can be moved and disposed of, such as in a biomass boiler.

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Forests face peril

Minnesota has an estimated one billion ash trees, the most of any state in the nation, including huge swaths of black ash forest in northern counties. In an effort to save some of those forest trees, Minnesota bug experts have released stingless Asian wasps in southern counties to see if they will feed on ash borers here as they do in China. The imported wasps have reproduced where they were released, signaling they are finding ash borers to munch on, but it’s too early to say if the wasps will actually slow the spread of the borers.

It’s believed ash borers hitched a ride to the United States in untreated pallets or packing crates from China and escaped in the Detroit port area in the 1990s.

The problem first surfaced when ash near Detroit and Windsor, Ontario, began dying off at an unusually high rate. By the time scientists figured out what the culprit was, in 2002, emerald ash borers already had infested almost every ash tree in five counties around Detroit.

Since then they have killed tens of millions of trees in 24 eastern states and Canada.

On their own, the bugs move very slowly - only a couple of miles per year. But because the bugs were moved in firewood and nursery stock, emerald ash borers have expanded their range by hundreds of miles annually.

Wholesale efforts to stop the bug from spreading have so far failed. Outside Windsor, forest managers cut thousands of healthy ash trees down to create a wide buffer that the borers couldn’t cross. But it turned out borers already had moved beyond the line, and they continued to spread.

The insect was first confirmed in Wisconsin in 2008, and now 20 counties are under quarantine.

Avoid moving ash borers

State officials advise three steps to avoid moving emerald ash borers:

Don’t transport firewood. Buy firewood locally from approved vendors and burn it where you buy it.

Be aware of the quarantine restrictions. If you live in a quarantined county, be aware of the restrictions on movement of products such as ash trees, wood chips and firewood.

Watch your ash trees for infestation. If you think your ash tree is infested, go to mda.state.mn.us/eab and use the “Do I Have Emerald Ash Borer?” guide.