Evil green invasion of the ash borer

Countywide quarantines, unified command, emergency response squads, a joint information center -- they're all part of a battle plan that Minnesota officials have prepared to combat a metallic-green, half-inch bug. The emerald ash borer has not yet shown up in Minnesota, but officials are sacrificing trees, setting traps and training volunteers as part of a statewide early detection system.

Brought to the United States in packing crates from China and discovered near Detroit in 2002, the invasive insect has killed more than 20 million ash trees in southeastern Michigan alone, and millions more in six nearby states and Ontario.

Louisville Slugger has even prepared a fact sheet on the borer, whose invasion could spread east to wipe out ash trees near the Pennsylvania-New York border that the company harvests to make baseball bats.

"I always tell people that if emerald ash borer arrives, you won't even remember Dutch elm disease, which is pretty scary," said Ralph Sievert, director of forestry for the Minneapolis Park and Recreation Board. That disease, a fungus spread by beetles, decimated millions of elms beginning in the late 1970s and left huge holes in urban forests where graceful boughs had arched across avenues.

Sievert said that the emerald ash borer could jeopardize about 38,000 ash trees in Minneapolis, which constitute 19 percent of the trees growing on boulevards in front of homes and businesses.

Another 170,000 ash trees are planted on private property or natural areas such as parks and parkways.

St. Paul has about 90,000 ash trees on public and private land, ,according to city arborist Chris Boche.

The stakes are even higher for the state. Minnesota has about 872 million ash trees growing on forest land -- second highest in the nation after Maine -- according to state officials.

"If we lose the species, it would change our whole landscape," said Val Cervenka, forest health supervisor for the Minnesota Department of Natural Resources. "The longer we can prevent the emerald ash borer from coming here, the more time we buy in learning how to manage it once it gets here."

Officials expect the borer will probably be detected next in Wisconsin but note that it can show up wherever infested wood is transported as nursery stock or hauled as firewood.

The emerald ash borer can only fly a couple of miles a year, said Cervenka, but firewood moves at 55 miles per hour. "Firewood restriction is our top priority," she said.

Last year Minnesota passed a law banning firewood from state parks, forests and other state lands unless it has been purchased from an approved firewood vendor. Effective May 1, any non-approved firewood brought onto DNR lands is subject to confiscation and a $100 fine, Cervenka said.

The Minnesota Department of Agriculture has prepared an elaborate plan designed for early detection of emerald ash borers. Last week, its officials watched as Minneapolis arborist crew leader Jim Spencer selected a healthy ash tree in a natural area along Minnehaha Parkway in south Minneapolis. It would be one of half a dozen in the city, and hundreds across the state, to become living lures for the borers.

Scientists in Michigan have learned that borers are more attracted to trees that are under stress, said MDA plant protection division scientist Mark Abrahamson. So the state program intentionally weakens the trees by removing some of their bark and skin, a process known as "girdling."

Spencer used a hand saw to cut through the bark encircling the tree, then pulled on a draw blade to shave off the bark between the two cuts and the thin layer just beneath the bark that carries water and nutrients from the roots to the crown.

Girdling a tree will essentially starve it in a couple of years, said Abrahamson, and it creates an odor that can draw ash borers from some distance if they're already nearby. The borers typically fly to upper leafy areas with plenty of sun, mate and lay eggs in crotches where branches meet the tree and the furrowed bark offers protection.

By returning to the tree this fall, cutting it down and stripping it, Abrahamson said, workers will be able to view whether any larvae that hatched from the eggs have burrowed into the bark and are feeding on the tree's vascular system.

About 1,300 trees were girdled across Minnesota last year, Abrahamson said, and none of those sacrificed last year showed any signs of the borers. Another 400 will be treated in the next few weeks for 2008.

The state has also acquired about 250 purple traps that are part of a national effort by the United States Department of Agriculture to detect ash borers. The three-sided traps are about 3 feet long and 1 foot wide and look something like a box kite, sticky on one side. They will be placed near the top of ash trees in about 50 locations, he said, including 20 state parks that receive large numbers of visitors from other states who might be carrying firewood from infested areas.

State agriculture officials also held six training sessions across the state during the past month to teach about 180 volunteers how to identify the ash borer. The reason for all of the prevention is to detect ash borers as quickly as possible, said Abrahamson, so that a rapid response plan can be activated to try to eradicate them or to initiate quarantines to confine their further spread within the state.

The state's plan, completed last year, would establish an incident command system similar to what's used when federal, state and local agencies respond to natural disasters such as hurricanes and forest fires.

But it's unclear whether anything can stop the bug. Sharon Lucik, public affairs specialist for the USDA near Detroit, said researchers in Michigan and elsewhere are studying whether the insect can be controlled by introducing tiny parasitic wasps from Asia, or by using pesticides.

Minneapolis and St. Paul stopped planting new ash trees during the past couple of years, but Sievert said that homeowners should not cut down existing ash on their property because of fear about an emerald ash borer invasion. "It could be a number of years before it gets here, you never know," he said. "But if someone's going to plant a new tree, we advise against choosing an ash."

That's a shame, said Minneapolis forestry program manager Jim Hermann, because the ash is an ideal urban tree: a tough species that grows quickly, provides great shade, and is able to tolerate poor drainage, mixed soils and winter salt and sand. He and others hope that the girdled detection trees in Minneapolis and elsewhere do not show any ash borers for a long time to come.

Abrahamson agrees but said it's also possible the borers have already arrived somewhere in Minnesota and haven't built up a large enough population to be detected yet. "The expectation is that southeastern Wisconsin will be the next place it'll be seen," he said. "It's not a question of if, but when."

Tom Meersman • 612-673-7388