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Emerald ash borers have invaded the Fort Snelling Golf Course, the first reported Hennepin County infestation outside of Minneapolis and one that puts the ruinous insects within sight of Dakota County.

It's the first new ash borer infestation found this year in Minnesota, which has quarantines in four counties to restrict the transfer of ash wood and limit the spread of the beetles. They were first spotted in the state in 2009.

The discovery, announced Wednesday by the state Agriculture Department, has nearby cities bracing for the arrival of the ash borers and officials trying to determine whether to quarantine Dakota County.

"A lot of us were waiting for the next infestation, and we're half surprised it took this long," said Gregg Hove, Eagan's forestry supervisor.

Recent checks of monitor traps throughout Dakota County showed no sign of the tiny green insects. But there are no traps along the Minnesota River across from the golf course.

In Mendota Heights, directly across the river, City Administrator Justin Miller said the outbreak may prompt the city to take action. "We'll have to ramp up public education efforts," he said.

A district forester with the Minneapolis Park and Recreation Board, which manages the golf course, was checking on storm damage last Thursday when he noticed an ash that looked dead on top and showed signs of woodpecker activity.

Looking closer, he found the telltale exit holes of adult borers.

'Like a flu virus'

This year had been quiet in terms of new outbreaks. But Brad Bonham, a national consultant to cities on the ash borer problem, said that a lull is often followed by a sudden outburst of detections. She said that's because the beetle is difficult to spot and may infest the tree for years before the damage can be readily seen.

"It's like a flu virus. You don't know you're infested now," she said.

Although ash borers most often spread when people move infested wood, it's possible for them to fly across the river, said Mark Abrahamson, who runs the state Agriculture Department's emerald ash borer program.

"They tend to move along corridors, but that doesn't prohibit them from moving across," he said.

Abrahamson said that he spotted infestation signs -- such as bark cracking -- on half a dozen trees at the golf course Monday, and believes there may be a few dozen more showing some symptoms. He suspects that trees in natural areas just off the course also might be infested.

The golf course has 82 ash trees, along with scores of other types, he said. The Agriculture Department will work with the Minneapolis Park Board and property owners to mitigate the problem.

"It's not something you ever eliminate, but you can manage the damage so it's not spreading," Abrahamson said.

Quarantine in place

The ash borers on the golf course could date back before 2009, when they were first found in Minnesota near Hampden Park in St. Paul. As a result, ash wood is prohibited from being hauled outside of Ramsey and Hennepin counties -- as well as Houston and Winona counties, where the bug has also been found -- without an agreement with the state Agriculture Department and an inspection.

Some trees don't show signs of infestation for as long as five years. And Abrahamson said it's difficult to pinpoint how they got to the golf course.

The Minneapolis Park Board owns a wood processing site across the road from the golf course to make wood chips and mulch. But the operator that leases it must follow state guidelines to grind wood into small enough pieces to destroy infesting larvae. And ash trees are disposed of quickly, forestry director Ralph Sievert said.

The infested trees on the golf course won't be removed until fall or winter to avoid moving active beetles from one spot to another, he said.

The golf course is about five miles south of the nearest outbreak site, in the Seward neighborhood of south Minneapolis. Infestations also have been found in Shoreview, on the St. Paul-Falcon Heights border, and at Summit Avenue and Dale Street in St. Paul.

St. Paul has removed about 3,000 ash trees since May 2009. Minneapolis has removed about 2,400 infested trees since 2010.

The emerald ash borer is believed to have arrived in the United States in the Detroit area in the 1990s, although it was not identified until 2002. It has since been found in 15 states and two Canadian provinces, and has killed millions of ash trees, which in North America have no resistance to the bug.

Staff writer Bill McAuliffe contributed to this report. Kevin Duchschere • 612-673-4455