Residents of Jackson County, Iowa — particularly those around Andrew and LaMotte — will see low-flying airplanes Monday and Tuesday, weather permitting, that will release tiny flakes onto the tree canopy in an attempt to slow the spread of an insect pest.

The flakes are bits of plastic treated with a chemical substance, or pheromone, that disrupts the natural mating pattern of the gypsy moth, which can be destructive to trees, especially oaks.

The treatment is in response to the discovery last year of unusually high numbers of gypsy moths in Jackson, Allamakee and Winneshiek counties, indicating that a population has taken hold.

The flakes will be spread over about 27,000 acres of public and private land, about 20,000 in the Andrew area and 7,000 in LaMotte.

Planes will fly over more acres that that — about 68,200 total — but they will treat only specific wooded plots, not row crops, pasture lands or waterways, said Robin Pruisner, state entomologist with the Iowa Department of Agriculture and Land Stewardship. 

By comparison, Jackson County has 415,252 acres total; 108,807 of those are forested. 

The cost of the treatment is about $7.70 per acre, or $189,000 total.

The treatment program is being conducted through a partnership among the Iowa Department of Agriculture, the Iowa Department of Natural Resources and the U.S. Department of Agriculture’s Gypsy Moth Slow the Spread Foundation.

People “will likely see the low-flying planes as soon as the sun is up on treatment days,” said Tivon Feeley, the forest health program leader with the Iowa DNR. Treatment is entirely weather-dependent, though. If there is rain, the work will be delayed until the next suitable day, he added.

The way the pheromone flakes work is that they “mask the female gypsy moth’s natural pheromones to confuse the males and make it more difficult to find the females,” Feeley said.

The pheromone is specific to gypsy moths, so it does not affect humans or other animals or plants, including moths and butterflies, Pruisner said.

Iowa is one of nine states, along with Illinois, Indiana, Minnesota, North Carolina, Ohio, Virginia, West Virginia and Wisconsin, on the front edge of the gypsy moth’s spread across the country.

Iowa is not considered “infested,” and the goal is to delay that from happening as long as possible.

Gypsy moths are a European species introduced to the United States in Boston during 1869. The moth has been slowly making its way westward, with entomologists monitoring populations in Illinois and Iowa  since the 1970s.

The moths eat the leaves of, or defoliate, more than 300 different species of trees and shrubs, with oaks a favored species. Each larva can grow up to 2 inches long and consume up to 11 square feet of foliage from early May through June.

When they are abundant, the caterpillars can completely defoliate trees. Although healthy trees can survive defoliation, repeated removal of leaves can kill a tree. Older, less-vigorous trees suffering from drought can be killed by a single defoliation.

Treatments will be June 29-30 in Allamakee and Winneshiek counties. In all, 158,649 acres of Iowa forestland will be treated.