Targeted spraying, rain kills spongy moth in Kenosha County

Aerial spray treatments applied this summer to control moth larvae defoliating an increasing number of trees in western Kenosha County appear to be reducing the invasive insect's population in a targeted area, according to local officials.

In late spring and early summer, the county's public works department oversaw two aerial treatments intended to control a site where an outbreak of spongy moths has been known to occur.

The site included the east side of Highway KD north of Highway C in the Town of Randall and the Village of Twin Lakes where a biological insecticide was applied on May 17 and June 23. The county, which plans to develop trails in the area, worked with property owners concerned about the costly ongoing deforestation by the larvae.

Rain, fungus

A wetter-than-average spring and summer also helped knocked out more mature larvae in wooded areas, said Vijai Pandian, horticultural educator for the Kenosha County branch of the University of Wisconsin Extension. The wet conditions allowed for the activation of fungal spores in the environment to grow and colonize inside the larval hosts, effectively killing them, according to Pandian, who reported results of the program to the county's Planning and Development Extension Education Committee.

The first application killed the newly hatched larvae, stopping them from making their way to the tops of trees. The second application destroyed another wave of hatchlings and egg masses in the targeted area. In between sprays, rain that triggered fungal spores also decimated larvae in their mid-development stage, he said.

By the end of June, he said many of the trees had regrown their leaves.

"They started to re-foliate because of all the rain we got," he said. "Thank God for that."

Risk of damage

He said the level of damage done by the larvae even at mid-growth, however, is significant.

"Can you imagine, actually, what would happen if the spongy moth went into about a fifth or sixth instar stage?" he said. At that point, the distinct crunching sounds from hundreds of thousands of larvae devouring trees would be audible, he said.

The dry spells of the last three to four seasons have also encouraged the pest to flourish, including last year's infestation, he said.

"What level of damage they had, we don't know yet and I think that has yet to be assessed," he said.

Because fungus and viruses in the environment kick in later to disrupt the caterpillars' feeding, affected homeowners will need to continue to use strategies to prevent young larvae from reaching the tops of trees.

Among the methods used to slow their spread include the application of sticky barrier band traps around tree bases to reduce the young caterpillar population and burlap wrap traps to lure larger larvae.

Moth population

He said this season's aerial spray was successful in saving targeted properties while minimizing the defoliation and stress levels on the trees, about 10% of which were lost due to the spongy moth, he said.

"Overall, the spongy moth population crashed down. I can't say 100%, but I would say at least 90%," he said. "What does it mean? Actually, its a classic example of climate change and its impact. If you did get some periodic rain during the springtime that we usually get ... we wouldn't have this issue."