Minnesota ready to kick some ash borer

The borer war is about to begin.

But set aside any hope that the invasive emerald ash borer can be eradicated from the Twin Cities.

The tiny bugs, discovered last week in part of St. Paul, have likely been in town for four or five years already, said Mark Abrahamson, plant protection specialist for the Minnesota Department of Agriculture. That means they've probably spread among some of the about 300,000 ash trees in Minneapolis and St. Paul, making eradication impossible.

Still, there's "real value in trying to bottle this up in the Twin Cities," said Michael Schommer, a spokesman for the Minnesota Department of Agriculture.

Friday, the state took the first step toward limiting the infestation, establishing quarantines on the transportation of firewood in Hennepin and Ramsey counties.

The next step comes Monday, when about 20 professional arborists will begin canvassing areas around where the insects were discovered -- near the intersection of Interstate 94 and Hwy. 280 -- in the hopes of determining how widespread the infestation has become. Those results will help determine what hope experts can put in protecting greater Minnesota's ash trees from the voracious beetles. The state has some 900 million of the trees, with the highest concentration in northeastern Minnesota, especially St. Louis County.

While it will take several weeks for the arborists to complete their survey, many homeowners don't want to wait that long to know whether the bugs are in their neighborhoods. Rainbow Treecare Co. in Minnetonka got hundreds of calls on Friday from people worried about their ash trees.

An arborist with Rainbow was the one who discovered the ash borers, beetles native to East Asia, as he was estimating a tree-pruning job on Wednesday in St. Paul's Hampden Park neighborhood.

John Lloyd, Rainbow Treecare's director of research and science, said that pesticides are available to kill ash borers, but not if 30 percent or more of the tree's canopy is dead. "Once you get to that level, the tree's game is over," he said.

Spraying the leaves or bark of trees is not effective in killing or preventing infestations, Lloyd said. What has worked in Eastern states that have been invaded by the pests are products that are injected into the tree directly or through its root system, he said, because borers need to come into direct contact with the poison to be killed.

The cost of treating an ash tree is about $100 a year per tree, Lloyd said, and the most common method is drenching roots with the pesticide.

That's not likely to be affordable for cities and counties if trees on public land are infested. St. Paul has about 90,000 ash trees on public and private land. Minneapolis has about 210,000, said Ralph Sievert, director of forestry for the Minneapolis Park and Recreation Board.

"It's a huge number," Sievert said. "People used ash as a replacement for elms because they grow fast and take off quick and have pretty good shade."

Abrahamson said it's too early to tell whether the area of infestation found in St. Paul is an epicenter or just one of many dispersed sites that could turn up in the next few weeks. In the meantime, homeowners shouldn't get out the chainsaws.

"There's no point in cutting your tree down before there's a problem with it," Abrahamson said.

The arborists will be looking for ash trees with dead or dying canopies, or bearing the squiggly trails of borers that have eaten into the bark. Once the scope of the visible damage is determined, the Department of Agriculture will install several hundred large purple traps beyond those areas to find the frontier of the insects' movements.

Tom Fields, who lives about 3 miles from the infestation, loathes the prospect of losing the four mature ash trees on his St. Paul boulevard.

"It's just the beauty is going to be diminished," Fields said.

For some neighborhoods, losing ash trees would be a bitter replay of the elms that were lost to Dutch elm disease during the past three decades.

Sievert said that Minneapolis crews will finish their spring tree planting season at the end of the month, and about 10 arborists will then inspect trees in the city for elm disease, ash borers and other health problems. He said that a couple years ago the city began removing ash trees that were defective or planted too near utility lines as an early stage of phasing them out. Sievert said Minneapolis will not cut down any healthy ash trees, because they provide shade and other benefits.

Tom Meersman • 612-673-7388