Gypsy moth spraying

Spraying for moths
An airplane treats an area of Wisconsin to help reduce gypsy moth population levels. (Photo courtesy of DATCP)


Officials hope for lonely gypsy moths after spraying activity

By Ted Pennekamp


On July 9, two areas to the east of Ferryville in Crawford County were sprayed in an effort to slow the spread of gypsy moths. Different parts of Crawford County have been sprayed in the past and the process is biologically interesting as a means of getting rid of the destructive pests. 

Through its Gypsy Moth Slow the Spread Program, the Wisconsin Department of Agriculture, Trade and Consumer Protection is hoping that male and female gypsy moths become very lonely this mating season. During the next few weeks, male gypsy moths may find it challenging to meet ‘that special someone’ because of efforts by state and federal agencies to interfere with their love life. 

Through much of July, yellow spray planes contracted by the US Forest Service in a joint project with DATCP, are applying a pheromone flake, or mating disrupter, to nearly 20 sites in a dozen counties in the western third of the state. Two sites totaling nearly 5,000 acres near Fairview in Crawford County were treated July 9. About 1/4 to a 1/2 cup of flakes per acre is applied, which is equivalent to one to two flakes per square foot of leaf canopy.

“Female gypsy moths do not fly. They give off a pheromone which is a chemical scent that attracts male gypsy moths,” explained Rick Hummell, public information officer for DATCP’s gypsy moth program. “The flakes that we apply to the tree leaves emit the same scent. This confuses the males and makes it more difficult for them to find a mate. Next spring, there should be far fewer gypsy moth caterpillars.”

The flakes are extremely thin, tiny pieces of green plastic that are about 1/8 by 1/16 inches. The flakes are applied to the tree leaves at a very low rate so they are not easily detected. Hummell said past research shows that the flakes can reduce gypsy moth populations by nearly 90 percent from one year to the next.

“We mix the flakes with a sticking agent that is similar to white school glue so the flakes adhere to the tree leaves. We use airplanes to apply the flakes at a rate of one-two flakes per square foot of tree canopy,” Hummell said. “The flakes don’t harm the gypsy moth in any way; it just makes it more difficult if not impossible for a male to find a female gypsy moth.” 

The flakes are not harmful to humans, animals, birds or other insects. According to the Environmental Protection agency, there is no health risk to humans nor have any adverse effects been reported during the nearly two decades that these pheromones have been used. The spraying of pheromone flakes began in Wisconsin in 1999. Hummell said that spraying began in Crawford County in 2004, but it has not been done every year.

Residents of Crawford County may have noticed the yellow spray planes recently and in the past. They take off usually before 7 a.m. and remain in each select area until spraying is completed. The planes fly just above the treetops, so they are very low and loud. 

“Some of our spray blocks are very large, so it takes several days to complete the entire application,” Hummell said.

Program staff completed treatments in the southern part of the state last week, including Crawford, Grant, Richland and Iowa counties, before heading north this week to treat blocks in Dunn, Chippewa and Eau Claire counties. Treatments will continue over the next couple of weeks, and finish for the year, in several northern counties (Rusk, Sawyer and Bayfield). Hummell explained that gypsy moth caterpillars develop in Wisconsin from south to north throughout the summer. There can be a month difference between when they develop in the southern part of the state and the northern. The spraying is designed to follow this development pattern.

Hummell said that the moths emerge from the pupa stage and live for only about two weeks, during which time they try to mate.

The traps that have been seen hanging in trees in various parts of Crawford County over the last several years not only capture moths, but aid in the planning of spraying. Hummell said that the traps lure male moths in with use of the female pheromone. The traps are usually put out in a grid pattern in early summer and then collected in late summer, said Hummell. The moths in each trap are then counted. Hummell said that traps in some areas may only have a few moths, while others in different areas may hold more than 1,000 moths each. The areas which have a high concentration are then targeted for spraying the next year because there are obviously reproducing populations in these areas, said Hummell, who noted that the western part of Wisconsin has higher concentrations this season.

The gypsy moth is a destructive, exotic forest pest that was accidentally introduced into the United States. It feeds on more than 300 species of trees and has defoliated tens of millions of acres since the 1970s. Gypsy moth defoliation can lead to extensive tree mortality, reduce property values, adversely affect timber and tourism commerce, and cause allergic reactions in sensitive individuals who come in contact with the caterpillars.

“We need to keep the damage and defoliation level down,” said Hummell, in noting that there can be more than 1 million caterpillars per acre in an outbreak area. One caterpillar can eat one square yard of leaves. “They can make it look like winter time,” said Hummell. “They are not fussy eaters.” Hummell said that the caterpillars feed on numerous species including aspen, willow and maple to name a few, but they prefer oaks, which, of course, are abundant in Wisconsin. 

Maps of the spray sites and more information are available on the gypsy moth website at

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