Taking out slugs without more insecticides

Slugs can be a challenge in minimal and no-till fields, where greater tillage isn’t an option

Most of the acreage in Pennsylvania is no-till and that means slugs can be a huge issue.

This has become such an issue that growers are reverting to using more tillage, said John Tooker, of the department of entomology at Penn State University He spoke at the recent FarmSmart Conference at the University of Guelph.

Why it matters: Farmers using no-till and cover crops have found greater challenges with slugs, so slug management is critical to the continued use of these conservation tillage methods.

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Tooker teamed up with a farmer from Pennsylvania, Lucas Criswell, and found that the use of rye interseeded into soybeans helped decrease the slug damage.

“They cut the damage [from slugs] to about half on the soybeans with another crop to feed on,” said Tooker. “The ground beetles increased with the rye, by about three times, compared to that with no rye between the rows.

“Just by having something else out there we are diverting their attention and we are decreasing their damage by half,” said Tooker.

Mollusks are non-selective pests and they love canola, soybeans and small grains. Although not an issue in many corn fields, Pennsylvania state farmers are still dealing with them in their corn.

Slug populations can grow exponentially throughout one season because their eggs survive cold winters, Slugs can lay 500 eggs in a year and as hermaphrodites, they can fertilize one another or themselves.

About 20 per cent of the mid-Atlantic no-till fields has yield loss from slugs, which is about 600,000 acres, said Tooker.

The pests are best controlled through tillage, meaning no-till farmers face the worst of the invasions.

Some farmers spray nitrogen on their corn crops, about 30 per cent urea-based, at night to burn them off but this also results in burned corn, said Tooker. No-till and cover crops make good natural habitat for slugs, but also for their natural enemies.

The addition of cover crops to a no-till system “enhances the food web,” said Tooker. “We are farming to maximize connections between species and the more predators we have in the field, the less we need to rely on chemicals.”

In terms of the gray garden slugs, ground beetles are the “lions of the no-till fields”.

Tooker and his team of researchers measured predator populations as as they increased, the pest feeding damage declined.

Tooker said insecticides are valuable, but foliar insecticides, soil insecticides and seed treatments tend to be overused.

Using insecticides to remove the feeding pest from fields comes with consequences when they are used too much. They decrease populations of bad insects, but they also damage beneficial insect populations and can cause environmental issues.

It’s important to manage only those pests the farmer has, said Tooker, to minimize the possibilities of damaging natural control mechanisms.

Criswell and Tooker tried another study as well to look further into the cover crop method.

Criswell planted soybeans into his winter rye cover crop, and then one to seven days later, burned off the rye with glyphosate. They found that the slugs fed on the dying rye more than they did on the corn and soybeans.

“That dying rye is more attractive to a slug than a growing corn or a growing soybean and we think it’s because there’s more of an available protein in that dying rye,” said Tooker. “Yet this is also a wonderful habitat for ground beetles and their allies, so the slugs are feeding there away from your cash crop, but they are also getting hammered by the predators.”

This practice also provides the benefit of using fewer herbicides and without insecticides, unless the field reached the economic threshold where spraying is recommended.

The Criswell family now is reaching the same yields with their cash crops, while using fewer inputs, said Tooker.

About the author

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Jennifer lives on a farm in Cayuga, Ontario and has a lot of experience in the many aspects of agriculture.

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