Humans likely carried ash borer to Anoka, Dakota counties, foresters say

The emerald ash borer, the invasive metallic-green beetle that's trashing the state's ash tree population, has arrived in outer-ring suburbs, and city foresters say it probably hitched a ride with humans hauling wood rather than migrating from other infested areas.

As the pest moves from urban boulevards and back yards to natural areas and 40-acre back lots, the infestation will "burn hotter" and be more difficult to manage, a state entomologist said.

State Department of Agriculture scientists confirmed Anoka County's first emerald ash borer infestation on private property in Ham Lake — the heart of the county — on March 25 after a tipster called in the suspicious tree to the department's Arrest the Pest Hotline. That's about 10 miles from the closest known previous infestation site, in the city of Shoreview in Ramsey County. It also puts the pest at the doorstep of the state's 25,000-acre Carlos Avery Wildlife Management Area, which borders Ham Lake.

In December, scientists identified the first emerald ash borer case in Dakota County, at Lebanon Hills Regional Park on the Apple Valley-Eagan border. That was about 6 miles from the nearest previous infestation, in Bloomington in Hennepin County.

The beetle's arrival in suburban counties is not unexpected, but city foresters said it's disheartening because it's suspected the pest didn't naturally migrate from infected regions, but that humans had a hand in its introduction.

"That kind of jump is pretty big. You would expect a more natural progression," said Blaine City Forester Marc Shippee. "It was probably someone who brought firewood."

Department of Agriculture Entomologist Mark Abrahamson agreed that humans probably played a role in carrying the pest to Anoka and Dakota counties, given the distances from the previous known sites.

Leaders in Blaine and Lino Lakes, both of which border Shoreview, have been preparing for the beetle for years, so city foresters were surprised to see the first infestation discovered to the north.

"The insect doesn't have to be very efficient because humans move it. It's very sad," said Lino Lakes Forester Marty Asleson. "It went to the first ash tree when it emerged from the wood pile."

Abrahamson, who has examined the infected trees, said the beetle arrived in Anoka and Dakota counties four to five years ago. That's how long it takes to see the damage to the trees, including split wood and tunneling tracks. Abrahamson said he used to try to pinpoint the starting point of each new infection but, given the years it takes to diagnose, has largely abandoned that effort.

Anoka County now joins Dakota, Hennepin, Houston, Olmsted, Ramsey, and Winona counties in a state and federal quarantine designed to slow the spread of the beetle.

Even with the newly discovered infestations, Minnesota has led the nation on management of the emerald ash borer, Abrahamson said.

Emerald ash borer larvae kill ash trees by tunneling into the wood and feeding on the trees' nutrients. Since its accidental introduction into North America around 2002, the pest has destroyed millions of ash trees in 24 states. It was first discovered in Minnesota in 2009.

Minnesota has approximately 1 billion ash trees, the most of any state.

Managing the outbreak in Anoka and Dakota counties will be more challenging than in urban neighborhoods. Abrahamson said it's not feasible to remove every infected tree in wooded areas.

"As it goes out of the metro and into natural areas, it is going to burn hotter," he said. "In natural areas, it tends to be something that is going to run its course."

Abrahamson said that is evidenced by the fact that the pest has spread more quickly in rural Houston County than in the Twin Cities.

Cities have managed emerald ash borer through a combination of pre-emptive ash tree removals and treatment. Virtually every city has stopped planting ash trees along boulevards and in public parks and is urging residents to inspect their own property.

Shoreview — the infection site closest to Anoka County — had its first case of the ash borer in 2011 and has been able to keep the pest isolated to the Shamrock Park area. The city removes diseased trees and treats healthy high-value ash trees near the affected neighborhoods.

Neighboring Blaine, anticipating the beetle's arrival, has been removing about 70 boulevard ash trees and 50 park trees each year for the past several years.

"We've removed a total of 500 ash trees, which is nothing compared to what we have," Shippee said. Boulevard trees are replaced for free if a homeowner is amenable. City staff also will help residents obtain information about treating trees on private property.

In Lino Lakes, the city is removing some ash trees from parkland and treating other "high-value"ashes along boulevards and in parks.

The Lino Lakes environmental board will also review the city's existing emerald ash borer management plan this spring in light of the Ham Lake infestation.

Shannon Prather • 612-673-4804