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Steam cleaning the Port of Tacoma to eradicate invasive snail

TACOMA, Wash. – Where other solutions failed, steamed snails appears to succeed.

Washington State University is working with the Port of Tacoma and the Washington State Department of Agriculture (WSDA) to eradicate the invasive Mediterranean vineyard snail using steam.

A blue tarp covers a small part of a large grassy area. A dark brown section of grass is right next to the tarp. In the background is a large tank, with hoses running from the tank to the tarp.
The steaming apparatus at work, next to a plot that had just been steamed.

“We’ve had a portable steam boiler system that we use to fight fungi,” said Gary Chastagner, a plant pathology and Extension specialist at WSU’s Puyallup Research and Extension Center. “This is definitely an unplanned use of the technology, but the results have been very positive.”

The invasive snails were first found on Port of Tacoma property in 2005. The total infestation covered about 300 acres of land held by the Port, Pierce County, and private owners, according to Jenn Stebbings, a Port of Tacoma biologist.

Traditional treatments, including debris removal, brush cutting, and molluscicides, or snail bait, were used on most of that area. But areas within a 10-acre plot at the port, where the invasive snail was originally found, have proved difficult to clear.

“It’s a wetlands area, so you can’t use snail bait when surface water is present,” said WSDA Eradication Coordinator Rian Wojahn. “We’ve been looking for years for another way to get rid of them.”

At a meeting two years ago talking about other projects, WSU research associate Marianne Elliott overheard people talking about the continuing snail problem and suggested the steam system could help.

How to steam invasive snails

The system consists of a trailer-mounted powerful boiler with a 300-gallon water tank, temperature sensors, hoses, and large plastic tarps. Swimming pool covers are used to retain heat.

Steam from the boiled water is released at several spots under the tarp, warming the covered soil.

Closeup of a gloved hand holding two glass vials full of snail shells.
Examples of the Mediterranean vineyard snails that invaded the Port of Tacoma.

The steam kills snail eggs and adults in the covered area. The process takes about four hours per plot, and they can do two 750-square-foot plots per day.

Treatment of infested areas will take a few weeks to complete, depending on weather. The colder the temperature, the longer it takes to heat the soil, Elliott said. Wet soil is more difficult to work with.

“This is a bigger area than we’re used to, it’s not a nursery with a small area infested with an invasive fungus problem,” Chastagner said. “But we did several test runs last year and it really worked well.”

The steam process isn’t targeted, so all plant life is killed in treated areas. As part of the permit for the steaming project, WSDA is seeding the affected area with native grasses and covering it with hay for protection.

Need for eradication

A black tarp on a field with steam seeping out from the edges. Two people stand nearby observing.
Steam escaping from under a tarp used to eradicate invasive snails.

Mediterranean vineyard snails love to feed on wheat. That’s a big problem in a state with a $700 million wheat industry.

“It’s a nasty wheat pest,” Wojahn said. “It’s gotten to Australia, and they can’t harvest the wheat. They gum up the harvesters. It would be a huge problem if the snails get away from the Port.”

This isn’t the first unplanned use for WSU’s steam system. Chastagner and his team have helped fight apple maggots near Twisp and treated yard waste in Okanogan County, among other projects.

“Steam is one of the oldest ways to fight agricultural pathogens,” Chastagner said. “It’s all about reaching the right temperature at soil depths where the targeted organism occurs. We think this will be very helpful for the Port as a way to eliminate this invasive species.”

Media Contacts

Gary Chastagner, WSU Department of Plant Pathology and WSU Extension, 253-445-4528