Phosphine

With the future prospect of increased levels of resistance in pest populations there is a need to use longer exposures for phosphine fumigation of commodities to retain treatment efficacy. Trials in grain bins and on floor-stored grain have shown that it is possible to maintain adequate concentrations of gas throughout the bulk for lengthy periods using phosphine in carbon dioxide from cylinders. An automated dosing system for cylinder-based phosphine has been developed and tested by the Central Science Laboratory. The performance of the dosing system was compared with the SirofloR system that has been developed by CSIRO in Australia. Both systems were tested in a silo containing 700 tonnes of feed wheat and in a floor store containing 150 tonnes of feed wheat. The automated dosing system coupled with re-circulation gave comparable results to the SirofloR system. It may not be possible to maintain an even gas distribution using the automated dosing system without circulation in windy weather or during times of widely fluctuating diurnal temperatures. An alternative to phosphine for grain treatments developed at CSL is the use of the exhaust gas from propane combustion, using a purpose-designed self-cooling burner. Bins of 1000 tonne capacity can be disinfested at a fuel cost of less than 50p per tonne. Current research is indicating that although very low levels (<1%) of oxygen are required to kill insects, somewhat higher levels can be effective at preventing breeding and reinfestation. A new approach to storage life protection could involve storage under modified atmospheres