Ag. Department plans gypsy moth treatment in Lowry Hill

The Minnesota Department of Agriculture's proposed treatment area.

The Minnesota Department of Agriculture is planning to apply a biological insecticide this spring in the Lowry Hill neighborhood and small portions of surrounding neighborhoods with the goal of eradicating a population of invasive gypsy moths.

The department plans on applying the insecticide three times using a small airplane or a helicopter, likely starting in May, Kimberly Thielen Cremers, the department’s gypsy moth program supervisor, said at a March 6 public meeting at the Kenwood Community Center. The treatments will occur five to 10 days apart, though the department hasn’t set exact dates yet.

The department’s goal is to completely eradicate the invasive moth from the area, Thielen Cremers said. That’s unlike goals at some sites further east where the moths have already established.

“In this site in Minneapolis, we’re not up against that population front,” Thielen Cremers said. “So our goal isn’t just to slow this population. We want to eradicate it.”

The proposed treatment area.
The proposed treatment area.

Gypsy moths have been spreading west across the U.S. since being introduced to the country in 1869, aided in part by human activity, according to the Agriculture Department. The moths have established in New York, Pennsylvania, Michigan and parts of Ohio and Wisconsin, among other states, along with the two northeastern most counties in Minnesota.

Gypsy moths hatch in May as caterpillars and feed for approximately five to six weeks, Thielen Cremers said. The caterpillars can completely defoliate trees over that time, she said, making trees more susceptible to diseases and other insects that can cause morality.

“(The moth) doesn’t necessarily kill a tree … but the tree becomes stressed,” Thielen Cremers said. “And it’s the stress that leads to tree mortality.”

Gypsy moth caterpillars prefer to feed upon oak, aspen, willow and birch trees, among others, Thielen Cremers said, but will feed upon over 300 different species of trees and shrubs. One egg mass alone contains 500 to 1,000 caterpillars, she said, which allows a moth population to establish quickly.

Thielen Cremers said gypsy moth caterpillars have hairs that can create negative responses for people with skin sensitivities and asthmatic conditions. The caterpillars can also devalue properties by stressing trees and can force state agencies to restrict the movement of wood and outdoor items into and out of an area, she said.

The caterpillars enter a pupal stage in early July and no longer feed once they subsequently leave their cocoons, Thielen Cremers said. The moths die before winter, and the cycle begins again in the spring.

Infestation found early

The Agriculture Department typically needs three years to find a new gypsy moth infestation, Thielen Cremers said, but it found the Lowry Hill infestation in a shorter timeframe because of the vigilance of a private landowner. She said the department found thousands of caterpillars when it visited the site last June and that the infestation was the worst she’s seen in Minnesota.

The department was unable to treat the infestation last summer, Thielen Cremers said, but it immediately restricted movement of tree branches, woody debris and other outdoor products from the area. The quarantine remains intact.

The department plans on treating the area with an insecticide that contains the active ingredient bacillus thuringiensis kurstaki, or Btk. The bacterium is naturally occurring and is only toxic to caterpillars who digest it, Thielen Cremers said.

It has a proven safety record with people, pets, birds, fish livestock and other insects such as bees, according to the Minnesota Department of Health.

Public health officials say Btk is not a public health risk, the agency says.

Thielen Cremers said that 50 percent of the product breaks down in less than four hours due to natural sunlight and that the spray is effective for three to seven days. She said people with severe food allergies or weakened immune systems may want to stay indoors during and immediately after treatment but added there’s no evidence the insecticide will affect any given group of people.

An aircraft will fly about 50 feet over the treetops to spray the substance, Thielen Cremers said, noting that it could be loud. The Agriculture Department conducts the treatments in the early mornings, as early as 5 a.m., to take advantage of weather conditions, she said.

The department typically lifts a quarantine in the middle of June, Thielen Cremers said. She said there’s a potential the department will have to treat the Lowry Hill area again next year.

The treatment will impact other caterpillars in the early stages of development, Thielen Cremers said, but she noted that gypsy moths typically hatch before monarch butterflies arrive in Minnesota.

The quarantine area includes 66 acres in the Lowry Hill neighborhood, and the proposed treatment area includes 310 acres in Kenwood, Lowry Hill and a sliver of Bryn Mawr. The Agriculture Department will send out mailers to households in the treatment area approximately two weeks before the treatment date, Thielen Cremers said. People can call the department’s Arrest the Pest toll-free line at 1-888-545-6684 for information on treatment times or to report sightings of gypsy moths or caterpillars, she said.

Visit to learn more about the proposed treatment and to learn more about Btk.