Phosphine as a replacement for methyl bromide for postharvest disinfestation of citrus
P. Williams, G. Hepworth, F. Goubran, M. Muhunthan and K. Dunn
Postharvest Biology and Technology Vol: 19 Issue: 2 Pages: 193-199.
2000
บทคัดย่อ
Methyl bromide is the only fumigant registered for disinfestation of citrus in Australia. However, it has been identified as an ozone-depleting chemical and its use is being restricted in accordance with an international agreement. The only alternative to a 2-h methyl bromide fumigation is cold treatment at 1°C for 16 days, and a more rapid alternative is desirable. The phosphine cylinder gas formulation ECO2FUME (phosphine with CO2 as a carrier gas) was recently registered for 15-h fumigation of cut flowers. This treatment was used as a basis for experimental fumigations of oranges infested with larvae of Queensland fruit fly, Bactrocera tryoni in a 900-l chamber. Uninfested oranges were included in all fumigations to check for possible adverse effects. A 16-h fumigation at 20°C with an initial phosphine concentration of 0.98 g m-3 resulted in 96.4% mortality of fly larvae. This was a promising result but the mortality achieved was insufficient to meet mortality requirements for interstate (99.5%) or export trade (99.9%). Exposure times, temperatures and phosphine concentrations were all increased in subsequent fumigations. In the final series of fumigations with export grade Washington Navel oranges the exposure time was 48 h, thermostat settings for the chamber heater were 23 or 25°C, initial phosphine concentrations were 1.67 g m-3 and the concentrations were topped up to ~0.7 g m-3 after 24 h. No adverse effects on the oranges were observed, and a mortality of 99.998% was achieved with >48000 larvae exposed. This would meet requirements for interstate trade and possibly also some international trade, particularly if incorporated as part of a systems approach.