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MNR planes to spray gypsy moth at Devil’s Lake, Kettle Moraine

If you see a low-flying aircraft spraying anything over the South Unit of Kettle Moraine State Forest or Devil’s Lake State Park in the next month, don’t worry.

The Wisconsin Department of Natural Resources will conduct aerial spraying operations through early June to control gypsy moth, an invasive species that, in its caterpillar stage, defoliates trees and can devastate forests during an outbreak, which occurs every five to ten years.

The moth, which was previously known as the gypsy moth, is one of the reasons Wisconsin has rules against carrying firewood.

In February, the Entomological Society of America adopted gypsy moth as the insect’s new common name. It is derived from the common name used in France and French-speaking Canada, “spongieuse”, which refers to the sponge-like egg masses of the moth, according to the ESA.

“(Gypsy) is an ethnic slur to begin with that was rejected by Roma people a long time ago,” ESA President Michelle S. Smith told the AP last July. “Second, no one wants to be associated with a harmful invasive pest.”

Aerial spraying is a means of controlling the pest, and the DNR has already carried out operations. The planes fly 50 to 100 feet above the trees to deploy the spray, an insecticide called Foray which contains a naturally occurring soil bacterium, Bacillus thuringiensis var. kurstaki (BTK). The bacterium kills the moth moth caterpillars when they ingest it.

Spongy moth larva.

The insecticide, which is approved by the Organic Materials Review Institute for use in organic agriculture, is not toxic to people, pets or bees and degrades naturally within 10 days. The DNR advises people with severe allergies to stay indoors during close-range applications, and notes that airplanes can be noisy, as they have to fly close to the treetops where the larvae feed.

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Andrea Diss-Torrance, invasive forest insect program coordinator for the DNR, said she was in the field for many of these spraying operations and described the insecticide as “dirty water” or ” a fine mist of stale beer” – something any Wisconsinite who’s been to a Brewers or Packers game is probably familiar.

So while you don’t want to get it in your eyes or mouth, it’s not harmful if it touches you, and you can easily wash yourself and your things, including cars.

Diss-Torrance said they try to spray early in the morning on weekdays, when people are less likely to be on the move, but operations can extend into the afternoon, depending on the weather. .

Exactly when they spray will also depend on the weather. They aim to catch the caterpillar 10 to 14 days after peak hatching, which usually occurs during dry, hot weather like this week. That means they could spray the week of May 23 and certainly before Memorial Day weekend.

Diss-Torrance said they would target two high-traffic areas in the parks where there are already fewer trees, so losing more would be a big deal.

“We have to keep these trees in place, because we cannot replace them,” she said. “These trees are super important and are what these parks are for. We need to have places where people can enjoy big, beautiful trees. … We put (the trees) in risky situations. They are no longer in the woods We compact the soil on their roots, we change the pH… If we put them in danger, we must protect them when they are threatened, and it is a threat that is easily managed, so it gotta do it.”

In the Kettle Moraine State Forest, they will address the trailheads for the John Muir biking and hiking trails and the Nordic skiing and hiking trails on County Road H east of Whitewater. In Devil’s Lake, they will spray the day-use areas on the north and south shores as well as the campgrounds on the north side, Quartzite and Northern Lights.

The day-use area on the south shore of Devil's Lake, which includes a beach, will be the target of an aerial spraying operation for the gypsy moth in May.

At both parks, signs and staff will warn visitors of spraying operations, and visitors can call the Spongy Moth Information Line (800-642-6684, option 1) to find out where spraying is to take place the next day. .

Treatments are narrowly targeted to areas where they are really needed, not only because they are expensive, but also because they cause minor ecological disturbance.

But Diss-Torrance said the areas they spray are already heavily disturbed by visitors anyway. And because surrounding areas are left untreated, other species that are affected, such as tent caterpillars, typically rebound into the treatment area within a few years.

“We’re not really concerned about disturbing the ecosystem at the North Shore Picnic Area (at Devil’s Lake),” she said. “It’s much more affected by what the people below are doing.”

Gypsy moth outbreaks

The spongy moth, however, takes longer to rebound, with large temporary population increases, or “epidemics,” occurring every five to 10 years.

A sponge moth egg mass can contain between 600 and 700 eggs.

In normal years, only two out of 600 or 700 eggs in an egg mass will survive, essentially replacing the existing population. But if conditions are right for survival, including dry, hot weather, that could jump to four or six per egg mass, and “that’s when the population takes off,” Diss said. -Torrance.

RELATED:Wisconsin sees increase in gypsy moth population thanks to dry spring and summer, asks residents to be on the lookout for egg masses

The caterpillars, which are about 2 inches long and have hairy tips and a pattern of dark red and blue spots, feed on 300 species of trees, but they are particularly fond of oaks and aspens.

Trees can withstand about 50% defoliation, Diss-Torrance said, but when they shed more leaves than that, they tap into their root reserves to do more. These root reserves would have been used to make leaves the following year, thus weakening the trees and putting them on a precarious path.

The DNR uses sprays and insecticides only for extreme situations; they are part of an overall pest management strategy that includes biological measures such as a fungus called Entomophaga maimaiga.

The fungus, which originated in Japan, managed to control the population there as well as in New England and Wisconsin during outbreaks in 2004 and 2010.

“It’s the pox equivalent for the gypsy moth,” Diss-Torrance said, noting that the fungus almost exclusively targets gypsy moths. “We mapped zero defoliation (in 2004). It was super effective. … We were really happy about that, and then it happened again in 2010.”

The effectiveness of the fungus also depends on the weather, as it needs cooler, wetter weather to thrive.

Even with effective biological control, however, DNR takes extra precautions — aerial spraying — in high-use areas.

“You can lose a tree here or there (in the forest), but in a picnic area you lose a single tree, that’s a big deal,” Diss-Torrance said. “That’s why we’re taking these more protective positions.”

The spongy moth feeds on more than 300 species of trees but loves oaks and aspens.

More information: The DNR is working to change all references in its documents to gypsy moth, but for now the department’s gypsy moth portal is

The portal contains information about MNR’s efforts to control gypsy moth, mitigation methods for your own property, sign up for email alerts on spray operations, and the gypsy moth information line (800-642-6684, option 1).

Contact Chelsey Lewis at [email protected] Follow her on Twitter at @chelseylew and @VoyageMJS and Facebook at Journal Sentinel Travel.