Within a month, state agricultural crews will begin eradicating colonies of little fire ants within about a 4-acre area of Waimanalo.

During a briefing about little fire ants, state Agriculture Department officials said Monday the colonies, pinpointed by a survey, will be controlled and eradicated in about a year. The department would then monitor the area for three years.

"We will continue treating until we don’t find anymore ants at the site," said Rob Curtiss, the department’s acting plant control branch manager.

In response to fears that those buying plants from nearby nurseries in Waimanalo might spread little fire ants elsewhere, state officials said little fire ants have been eradicated from some garden shops, landscape plantings and nurseries.

Officials said the remaining colonies are confined to state agricultural land, which is situated outside nurseries, in hedgerows and gulches.

"They’re not in any nurseries. They’re not in any used areas," Curtiss said.

State agricultural officials plan to mark the ant-infested areas with tape and stakes to warn the public to steer clear.

Little fire ants were found on Hawaii island in 1999 and on Maui and Oahu in hapu logs from Hawaii island in December 2013.

Five Oahu nurseries, three of them in Waimanalo, were found to have small infestations of little fire ants, according to the state Department of Agriculture.

The colonies on Maui, on roughly 4 acres, have been eradicated, the department said.

Officials said that by the time state officials discovered fire ants on Hawaii island, they were too widespread to eradicate and there weren’t the kind of measures now available to kill them.

The little fire ants establish their colonies in trees, sometimes falling and biting people and probably responsible for blinding pets, officials said.

State officials fear the ants, if left unchecked, could severely affect the visitor industry.

Little fire ants, measuring about a 16th of an inch long, are pale orange in color and issue painful stings.

"There’s a lot of social and economic repercussions to having little fire ants," Curtiss said.

Curtiss said the infestation on Hawaii island has prompted some farmers to abandon their fields because they can’t find workers willing to pick their crop.

The state said the survey looked at about 50 acres near Kumuhao and Mahailua streets in Waimanalo and found billions of little fire ants on 4 acres. The state will use a combination of measures to eradicate the colonies, including pesticides and cutting trees.

"It’s still within the realm of things we think we can eradicate," Curtiss said of the areas.

Neil Reimer, the department’s Plant Industry Division administrator, encouraged people to send in a sample of their ants if they suspect them to be little fire ants. State officials said one way to test for little fire ants is to leave a chopstick with smooth peanut butter near plants in the shade in their yard. The little fire ants are attracted to nonchunky, nonorganic peanut butter, Curtiss said.

After an hour, if it has suspected little fire ants, the stick can be put in an airtight plastic bag, labeled with an address, and mailed to the state Department of Agriculture.

"We really need the public’s input," Reimer said. "The more we can get, the better it is that we can protect Oahu."