Development of a hot water disinfestation treatment for taro exported from the Pacific Islands

Taro imported to New Zealand from the Pacific Islands are currently fumigated with methyl bromide (MB) for control of mites, nematodes and other quarantine pests. There are growing restrictions on the use of MB, and alternatives to this fumigant are being sought, such as hot water treatments. Mites (Rhizoglyphus minutus) and nematodes (Meloidogyne sp. or Helicotylenchus sp.) were exposed to hot water both ‘on’ and ‘off’ taro. Hot water exposures ranged from 47.5°C to 52.5°C for 15 s to 5 min, the duration depending on the temperature. Preliminary ‘off taro’ experiments indicated that 100% mortality of R. minutus mite adults was achieved in 3–4 min at 47.5°C, and between 30 s and 1 min at 50°C. All adult mites were dead at the shortest treatment duration (15 s) at 52.5°C. The results indicated that 100% mortality of juvenile Meloidogyne sp. was achieved in 1–2 min at 47.5°C, and between 30 s and 1 min at 50°C. All juvenile nematodes were dead at 45 s at 52.5°C. Preliminary ‘on taro’ experiments at 52.5°C for durations of 3.5 min and 5 min indicated that a longer duration would be required to achieve 100% mortality of Rhizoglyphus mites. No live Meloidogyne or Helicotylenchus nematodes were present in either the untreated or hot water-treated taro.