Ash borer creeping to more cities

When Bloomington's tree guy, Paul Edwardson, got a call earlier this month from the state warning him that the emerald ash borer had attacked trees 2 miles from the city border, he wasn't surprised.

He'd been waiting for the call for three years, ever since the insect was discovered in St. Paul.

"We knew it wasn't a matter of if it would happen, it was just when," Edwardson said last week. "You plan for the worst and hope for the best."

Bloomington and Richfield are now at the front lines of the destructive bug's advance into the metro area, with Edina not far behind. Two weeks ago, the state announced that the borer had been found in trees on the Fort Snelling golf course.

The emerald ash borer larvae tunnel under the bark of ash trees, destroying the tissues that move water and nutrients. Signs of emerald ash borer include a thinning canopy and woodpecker activity in trees. But often a tree has been infected for years before it is noticed.

With no natural enemies in this country, experts expect the insect to eventually kill many if not most of the estimated 998 million ash trees in Minnesota. There is little to stop it from spreading except county quarantines on transporting cut wood and applications of insecticide to individual trees.

Bloomington, Richfield and Edina have taken different tacks to deal with the threat, but they all said they are sticking with existing policy.

After the Ft. Snelling infestation was announced, Bloomington set up a page about the bug on the city's website (it can be seen at www.startribune.com/a1658). Edwardson said he hasn't gotten any recent calls about the borer.

"Maybe there's a little bit of complacency, but part of it is that most cities have tried to keep people educated with up-to-date information," he said.

After the borer was found in the state in 2009, Bloomington added ash trees to its list of prohibited nuisance plants. No more ash trees could be planted in the city. Even before the borer was discovered in the state, Bloomington had been planting few ash and never offered them in its city-sponsored spring tree sale because of concerns about overplanting, Edwardson said.

During the winter, Bloomington has been removing sickly and weak ash trees on public property. That effort may take on a little more urgency now, he said.

In Richfield, Public Works Director Mike Eastling said his department sent a memo to the City Council after the Ft. Snelling news was announced. Richfield has adopted a very different policy from most cities, deciding that its ash trees are a critical part of the city's urban forest and spending $150,000 over the last three years to inoculate trees on boulevards.

Edina has done a tree inventory on maintained parkland but has chosen not to treat ash trees. City Forester Tom Horwath said he, too, thought they were being overused in the landscape and the tree is not a predominant species in the city.

"We didn't stuff our parks full of ash trees," he said. "I haven't planted an ash tree for the city in 22 years."

A handful of calls from Edina residents came in after the Ft. Snelling announcement, Horwath said, but the city usually refers them to the state. Horwath said he is concerned about some homes and industrial campuses in the city "with nice significant ash trees that were planted 30 or 40 years ago."

"It'll make a difference in the landscape," he said. "But for the city itself, we don't have ash-lined boulevards, so it's not so alarming for the city of Edina."

In all three cities, officials are recommending that if homeowners choose to treat their trees they hire a professional to inoculate their tree rather than use one of the soil drenches that are available. Chemicals that are dumped on the ground can get into storm water systems, affect non-target plants and poison good bugs like pollinating bees and aquatic insects that fish feed on.