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  Effectiveness of Hot Water

Hot water (49°C [120°F] for 12 minutes) has long been used as an effective treatment against insects of quarantine significance on cut flowers and potted plants. The DLNR Division of Forestry and Wildlife tree nursery in Hilo and an agricultural engineer from the University of Hawai'i at Hilo designed and built a hot water treatment facility and did some testing to determine the lowest possible lethal temperature for frogs that would also reduce incidence of heat damage to treated plants.

Results indicated that a 45°C (113°F) treatment for 3 minutes was adequate for killing frogs and their eggs. Applied as a shower, this hot water treatment has been effective on frogs and eggs in potted and landscape plants. Heat damage to plants was reduced or eliminated by following the hot water shower with 1-2 minutes of cool water. Orchids and bromeliads were the only plants tested that were sensitive to the treatment. Coqui frog eggs directly dipped in hot water for 3 minutes had a lower rate of hatching compared to untreated eggs of the same age.

treating Coqui frog eggs in hot water
Treating coqui frog eggs in hot water (113°F)
for 3 minutes reduces their rate of hatching.
untreated eggs
4 days after hot water  treatment
Untreated eggs 4 days after hot watertreatment
(113°F for 3 min, 1 min cooling)
(Note fungus beginning to engulf nonviable eggs)

Hot water shower:
hot water system

plants being showered
a) Hot water system to disinfest tree seedlings of frogs prior to planting (Division of Forestry and Wildlife, Hilo) b) Close-up of plants being showered for 5 min with 113°F water followed by 1 minute of cool water.

Photos by S. Chun and A. Hara, UH–CTAHR


A plant nursery constructed a hot water shower container to disinfest potted plants of frogs and eggs prior to shipment and sales.  Various plant species were treated at 113-115.6°F to determine their tolerance to hot water.  Treatment caused mortality of adult coqui frogs and eggs in 10 minutes.  This trial demonstrated that hot water treatment is feasible and effective on a commercial scale. View photos of the facility, process, and results.

All research on coqui frogs reported here was conducted in compliance with the University of Hawai`i Institutional Animal Care and Use Committee (Protocols #02-029-3, 02-043-3, 02-028-3).

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