Federal and state officials are proposing to spray 133,275 acres in Cook County this summer in an attempt to slow the spread of destructive, exotic gypsy moths.
The proposed treatment area is more than 40 times the size of the largest area previously treated in Minnesota.
"This is going to be large," said Kimberly Thielen Cremers, the state's gypsy moth program coordinator. "The largest blocks were back in 2002, when we treated 3,000 acres in the Twin Cities area."
The U.S. Forest is seeking public comment on the proposal, under which low-flying aircraft will spread tiny plastic flacks embedded with a synthetic pheromone.
The chemical doesn't harm moths, but it mimics the scent that female gypsy moths use to attract mates. Flooding an area with pheromones confuses the male moths so they can't find mates and reproduce.
"It's about the lowest-impact treatment that the agencies have found to be effective in slowing the spread of gypsy moths," Superior National Forest spokeswoman Kris Reichenbach said.
The chemical is so specific for gypsy moths that it's used in areas where federally listed threatened or endangered moth or butterfly species are present.
Officials plan on applying the chemical in late July or early August.
"What we are proposing is treating some 133,000 acres in four blocks," Reichenbach said. "It's mixed ownership. The majority is on federal Forest Service land, but to really have an effective treatment, we need to look at blocks."
The chemical and spraying costs will average about $8.35 an acre.
"We know we're not going to knock this population out completely," Thielen Cremers said. "We're just hoping to slow it down enough to buy us some more time in regards to management."
Officials decided to treat the area after the Minnesota Department of Agriculture's annual trapping program discovered a record number of male gypsy moths in the area.
In fact, the number of moths trapped in Cook County jumped 458 percent between 2004 and 2005. The moths caught in Cook County comprised 82 percent of all the gypsy moths caught in the state during 2005.
The sudden increase in moths in Cook County surprised officials last fall. They speculate travelers may be one reason for the increase, since gypsy moths lay eggs on vehicles, boats, trailers and camping equipment.
Weather also might have helped the moths.
"We had an abnormally warm summer, so there were ideal conditions up there for gypsy moths," Thielen Cremers said. "A lot of times cooler temperatures kind of hold them at bay. Hopefully this winter has knocked them back a bit."
Gypsy moths are not native to North America, so there are few if any natural enemies to slow their westward spread.
Before hatching into moths in midsummer, gypsy moth caterpillars can defoliate large sections of forest, with oak, aspen, birch and willow among their preferred meals. They eat more than 300 tree and bush species.
Unlike forest tent caterpillars, whose populations cycle up and down, gypsy moths can remain strong year after year, defoliating trees repeatedly and stressing forests.
In some cases, tree growth can be slowed and trees already stressed by other causes can be killed. One Wisconsin study showed up to 20 percent of defoliated trees died.
This will not be the first time crews have battled gypsy moths in northern Minnesota. So many moths were trapped near Tower in 2004 that crews returned last spring and used airplanes to spray a bacteria to kill moth caterpillars on about 640 acres. It was the first eradication effort in northern Minnesota.
A lower moth population density in Cook County caused officials to decide to use the pheromone rather than the bacteria.
"We have a more scattered, low-level population, not as concentrated as we had in the Tower location," Thielen Cremers said. "Pheromone is best for this population."
Cook County isn't the only Minnesota area where authorities will battle gypsy moths this year. At the request of the Grand Portage Band of Chippewa, the MDA plans to treat 2,087 acres of the reservation with bacteria in early summer. An area near the Twin Cities also is slated for bacteria treatment.Duluth News Tribune
