DNR halts gypsy moth spraying in much of state

Weather boosts fungus that kills caterpillars

The Department of Natural Resources is suspending a once highprofile program involving planes that swoop low and spray insecticides over areas infested with gypsy moths — an invasive pest that first defoliated Wisconsin trees in 1997.

The action ends a regimen begun in 2001 of aerial spraying, using naturally occurring insecticides that target known infestations of the leaf-munching insects in the eastern two-thirds of Wisconsin.

The change approved on Wednesday by the state Natural Resources Board has been in the works for several years. Experts say it’s an indication the suppression program has kept populations of gypsy moths at bay.

The biggest year of the program was in 2004 when spraying covered 51,450 acres. That year, planes swept over nearly 1,000 acres in Milwaukee County.

But while the DNR is suspending its efforts, another state agency will keep spraying with another strategy in mind, which owes to Wisconsin’s location and role in a national effort to combat the gypsy moth.

Wisconsin’s western counties represent the leading edge of gypsy moths’ spread, so a separate, larger spraying program managed by the Department of Agriculture, Trade and Consumer Protection, and coordinated with federal authorities, will continue in an effort to blunt the expansion.

With the U.S. Forest Service paying roughly two-thirds of the cost, the cost of the defensive spraying has averaged more than $2 million annually in Wisconsin since 2010, federal figures show.

To the east, however, “it’s become spotty — it’s small,” Andrea L. Diss Torrance, a plant pest and disease specialist with the DNR, said in an interview before the board’s action in Green Bay.

Diss-Torrance said that with outbreaks now found in smaller, isolated areas, an infrastructure of private aerial applicators and arborists are in a better position to take on the gypsy moth.

“It’s time to step back and let private business take over,” she said.

Entomologist Patrick Liesch of the University if Wisconsin-Madison’s Insect Diagnostic Lab agreed with the DNR’s strategy. “It’s really come down,” he said. “There isn’t the demand there once was.”

He said rainy springs in recent years have unleashed a fungal disease known as entomophaga maimaiga that kills gypsy moth caterpillars.

The impact of the fungus got a boost beginning in 1997 when the DNR spread soil and gypsy moth cadavers containing the fungus at strategic locations for three years — an innovation now used in other states.

The fungus then spread naturally, Diss-Torrance said. “Once we got it started, it pretty well took care of itself,” she said.

In its caterpillar form, the gypsy moth damages trees when it congregates in high numbers, usually during the months of May and June. A prized target is oaks, but many tree species are affected.

Wisconsin’s last large gypsy moth infestation occurred in 2010, when 346,749 acres were defoliated, according to DNR figures. That appears to be an anomaly: Since 2014, fewer than 100 acres have been damaged in any one year.

Liesch said the situation contrasts with the emergence of emerald ash borer, another invasive species that continues to spread across the state and is causing widespread devastation.

Liesch also said that another emerging pest is the invasive brown marmorated stink bug, which can cause problems for fruit growers, home gardeners and landscapers.

(It also invades homes and its trademark odor, sometimes described as rotting food, is released when the bug is threatened or killed.)

Wisconsin’s last large gypsy moth infestation occurred in 2010 when 346,749 acres were defoliated, according to DNR figures. That appears to be an anomaly: Since 2014 fewer than 100 acres have been damaged in any one year.

The gypsy moth arrived in the U.S. in 1869 when growers tried breeding silkworms to survive the North American climate. Two decades later, authorities were getting reports of gypsy moth infestations after some escaped.

The goal of a federal-state “slow-the-spread” program in transition states such as Wisconsin, Illinois and Ohio is designed to keep the bug out of states to the west.

In Wisconsin, an average of more than 180,000 acres have been sprayed annually between 2010 and 2017, Forest Service figures show.

This year, it dropped sharply to 70,230 acres.

It’s unclear if this represents a trend, said agriculture department spokeswoman Donna Gilson, “but rather it depends a lot on what is happening in other states along the frontier of the infestation.”