WAIMANALO — The nursery business has a potential new weapon against the pesky coqui frog, using heat to kill the animal in potted plants.

In a test done at Leilani Nursery last week, nine out of 10 frogs died after being exposed to temperatures of more than 113 degrees for five minutes.

The frog that survived had burrowed in the dirt of a potted plant. However, the frogs don't normally burrow into the soil, and the tester said he could overcome the problem.

Bill Durston, owner of Leilani Nursery, said the goal is to kill 100 percent of the frogs in potted plants being prepared for export, and that he'll run more tests to see how much more exposure it will take to kill all the frogs.

"This is a prototype ... to stop the spread of coqui frogs and possibly other insects," Durston said, adding that he is ready to move to full production of the system.

The plants are treated to a hot shower in an insulated chamber the size of a shipping container for about 20 minutes.

The plants seem to enjoy the bath and come out glossier and brighter, according to Durston, who said the idea came from University of Hawai'i researcher Arnold Hara, who discovered the coqui's sensitivity to heat. UH researchers also helped him obtain a $22,000 grant to build the 8-by-8-by-20-foot chamber.

Hara, an entomologist with the UH College of Tropical Agriculture and Human Resources, said the heat treatment process has been around since the 1920s but had lost popularity with the advent of chemicals. Now with the prices of chemicals rising and strict regulation of chemical use, the cost-effective heat treatment is making a comeback.

"It's not only for the treatment of coqui — it's a control for other quarantine pests," said Hara, adding that he's looking into using the process for fire ants, stinging caterpillar, snails and slugs. "It's effective and it's nonchemical. There's no toxic residues."

Loved in their native Puerto Rico, coqui frogs are loathed in Hawai'i for their shrieking. Big colonies have established themselves on the Big Island and Maui.

O'ahu's biggest colony of coqui frogs in Wahiawa recently was brought under control with the help of the O'ahu Invasive Species Committee and the state Department of Land and Natural Resources. A crew has been spraying citric acid three to four times a week for the past year, said Scott Williamson, with Forestry and Wildlife.

The frogs are believed to have hitched a ride to Hawai'i in plants shipped from Puerto Rico or Florida in the 1990s. Here there are no natural predators, such as snakes, to keep the coqui numbers under control.

The heat treatment won't eliminate the species, Durston said, but if successful, it would make it possible for growers to guarantee that their plants are coqui-free when they ship interisland or out of state.

State, UH and Guam officials witnessed the test and were impressed with the results.

Guam has not allowed large shipments of plants from Hawai'i for several years because of the coqui frog, said Russell Campbell, administrator for the Guam/USDA Plant Inspection Station.

Campbell said he's impressed with the treatment and could see Guam opening its doors to plants from Hawai'i again.

Reach Eloise Aguiar at eaguiar@honoluluadvertiser.com.