Ash borers hit West River Parkway

For the first time, emerald ash borers have crossed the Mississippi River and been detected along West River Parkway in south Minneapolis.

The invasive insects, discovered in St. Paul in 2009, spread to the Prospect Park neighborhood of southeast Minneapolis last year. They typically kill trees within five years.

Minneapolis forestry crews will cut down about 100 infested trees in both areas within the next two weeks.

"The significance here is that it's a new part of the city where we haven't really dealt with emerald ash borer yet," said Mark Abrahamson, entomologist for the Minnesota Department of Agriculture.

Abrahamson confirmed five infested trees along the top of the west parkway bluff near the railroad bridge at East 27th Street. He also identified 13 trees that are suspected of being infested.

All of the infected trees will be removed.

The bugs have spread to another 78 ash trees in Prospect Park, said Michael Schmidt, assistant superintendent for operations for the Minneapolis park system. The trees range from 3 to 18 inches in diameter, he said. They are mostly on the Malcolm Avenue side of the park, near the "witch's hat" water tower. Last year bugs were found in four trees in the park.

The small, green beetles came from China, likely in crates or pallets in the 1990s. They were first found in the Detroit area in 2002. They have killed millions of ash in Michigan, and spread to 12 more states and two Canadian provinces.

Most of the spread is through firewood, since the insects can fly only a few miles each year during the few weeks that they have wings. Its larvae bore into trees, grow under the bark, and eat away at vessels that carry water and nutrients.

Minnesota is especially vulnerable. It has an estimated 998 million ash trees, tops in the nation, said state agriculture spokeswoman Liz Erickson.

Schmidt said Minneapolis has more than 30,000 ash trees on its boulevards, with an average diameter of 12 to 18 inches.

Since the trees are likely to become infected eventually, the city last year removed 1,400 ash that were poorly formed, interfering with phone or electric wires, or otherwise unhealthy, he said. They will be replaced with other species this spring, he said.

"The surprise in St. Paul is how few infested trees we've found outside of that neighborhood," he said.

But Abrahamson has found two new "hot spots" about half mile away. About one-fourth of 250 ash trees are infested in woody patches just north of Energy Park Drive, he said.

Trees with ash borers are difficult to spot because the bugs live under bark. Woodpeckers prey on them, Abrahamson said, flaking off outer bark and leaving light patches and dime-sized holes. This is the best time to spot that evidence, he said, before leaves begin to emerge.

One bit of good news is that the life cycle and population growth of borers may be slower in Minnesota than elsewhere, perhaps because of its colder winters, he said.

The Agriculture Department will set out 4,500 traps across the state during the next week or two, he said. The aim is not to catch vast number of insects, but get an early warning sign of where borers may be present. They sprout wings and emerge from trees in late May.