The Hawaii Department of Agriculture this morning resumed plans to drop a citric acid solution over a remote mountain area of Waimanalo as part of efforts to eradicate invasive coqui frogs.

Helicopters were initially scheduled to drop the solution via “bambi buckets” back in the third week of April, but the operation was postponed due to high winds, as well as last week due to weather conditions.

The department said after a rain delay this morning, the treatment began at about 10 a.m. The helicopter made a total of 83 drops of the citric acid solution over 4 acres of the coqui infestation.

Officials said area residents and businesses have been continually informed of the planned treatment schedule, weather permitting.

They said the citric acid solution is a formula that has been successful in controlling and eradicating coqui in Hawaii in the past, and should not physically impact the neighborhood, and that helicopter noise will be intermittent.

The department first detected the coqui frog infestation in April 2021 along the base of the mountains in Waimanalo, where 65 frogs had initially been hand captured.

Since then, Jonathon Ho, the department’s Quarantine Branch Inspection and Compliance Section chief, said an estimated 600 coqui frogs have been caught in the past year or so.

“How the frogs got there, we’re not quite sure because they’re so remote,” he said in a video interview. “We’re just looking to eradicate it.”

Ho said there is another, smaller infestation of coqui frogs in Palolo Valley. That one, however, is “nowhere near the scale or remoteness of this particular infestation,” he said.

The invasive, small tree frogs known for their piercing, nocturnal “KO-KEE” calls, were first detected on Hawaii island in the late 1980s, where they have taken hold.

The state Department of Land and Natural Resources said besides being a major noise nuisance, coqui frogs pose a threat to native ecosystems, and compete with native birds for insects.

Upon discovery of the Waimanalo infestation, the state Agriculture Department joined forces with DLNR, the Hawaii Invasive Species Council, Oahu Invasive Species Committee, and the Department of Hawaiian Home Lands to eradicate this coqui population.

DLNR said the treatment should have no significant impact on protected species in the area.

Ho said he expects this to be the first of multiple treatments. To consider the population eradicated, he said officials would have to hear no coqui frogs for at least eight months.

“There will be monitoring by staff, which we will continue to do on a bi-weekly basis, and then obviously we will then treat as needed,” he said.

Anyone who hears coqui frogs on Oahu, Kauai or Maui County should call the state’s toll-free hotline, 808-643-PEST (7378).