SAN PIERRE, Ind. – Researchers from Purdue University are trying to solve a problem mint growers are having with crop loss from the Asiatic garden beetle, an invasive species that feeds on the hair-like roots of the plants.

The jury is still out but the ongoing research at a mint field in the northern part of the state is showing early positive results.

“I’m very excited about this. It’s been a lot of work,” said Elizabeth Long, an entomologist at Purdue.

Long is leading the ongoing effort primarily at the 800 acres of mint farmed by Larry Wappel Sr. and his son, Larry Wappel Jr. in Starke County.

The objective is to kill the grubs while they’re still underground with nematodes, which are ground burrowing round worms and a natural predator of the beetle.

In September, Long said nematodes were applied in some areas of the fields and recent soil samplings revealed they were still there in strong numbers. 

Long said soil samplings to be taken in the coming months when the grubs are large enough to see will reveal if there’s been a reduction in the amount of the plant-killing species.

“That’s what we’ll know come this fall when we go out and do that next sample,” she said.

The hope is the nematodes through reproduction will grow in numbers to control the grubs permanently without use of insecticides on the perennial mint plants. The grubs hatch from the eggs of the female Asiatic garden beetle and burrow into the ground, then feed off the roots of the plants.

Long said the infected plants wither and can die from their damaged roots no longer being able to supply a sufficient amount of nutrients.

Wappel Sr. said problems with the Asiatic garden beetle at his farm started about 10 years ago. His crop losses of up to 50 percent in some fields have been heaviest in more recent times.

“When you have the number we have had the past three years, it’s just impossible to grow mint unless we treat it,” he said.

Wappel Sr. said he has insecticide but he doesn’t want to use it unless he has to.

Long said insecticide will kill the grubs as they ingest the chemicals from the roots but whether a need exists can be difficult to gauge since beetles are difficult to notice as they fly only at night.

There’s also a belief insecticides will have an impact on the flavor and other qualities of the mint used in products like chewing gum, candy and skin products.

“Insecticide, if applied, is then in all of the plant tissues,” she said.

Long said not all mint growers are being impacted by the species, which seem to thrive best in sandier soils.

The Wappel mint farm in San Pierre grows strictly peppermint. One of their major customers is the Wrigley Co., widely known for its chewing gum.

According to USDA, more than 80 percent of mint production in the U.S. happens in Washington, Oregon and Idaho, while much of the rest comes from Indiana, Wisconsin and Michigan.

Long said she began putting together the framework of her research after the Wapple reached out to her in 2020.

She received grants from USDA to help cover the costs of her research, which included purchasing nematodes the Wapples applied to their fields with traditional farm equipment.

“If we don’t treat this stuff, we don’t have a sustainable crop,” Wappel said.

Corn and soybeans are the primary crops at his farm, which also grows other specialty crops like potatoes and cucumbers.