As increased amounts of grain are being stored on-farm, with growers holding their produce until their pre-determined prices are reached, it is important the grain quality is maintained and the threat of insect depredation is averted.
An on-going study involving Dr Greg Doran from Charles Sturt University’s School of Agricultural and Wine Sciences in collaboration with Dr Mark Stevens, a principal research scientist with the NSW Department of Primary Industry, Wagga Wagga is investigating the efficiency of fumigation using the thermo-siphoning system for grain silos.
The absolute control of insects is an imperative, according to Dr Doran and especially in this era of fast-moving and ever changing international trade negotiations.
“There’s zero tolerance for live pests in grain off-farm and the most common control method is fumigating using phosphine gas,” he said.
Dr Doran said the aluminium phosphide tablets are incorporated into the grain through the augurs as the silos are filled or alternatively the tablets are hung in the headspace of the silo or in a fumigation box and a fan is used to circulate the phosphine gas.
“Thermo-siphoning phosphine in silos is a more recent development and involve the use of solar radiation to warm air in an external pipe, causing it to rise to the top of the silo, carrying phosphine from a fumigation box at the base of the silo,” he said.
“The greater density of phosphine relative to air causes the phosphine to sink to the bottom of grain chamber, fumigating the grain in the process.”
Thermo-siphoning phosphine in silos is a more recent development and involve the use of solar radiation to warm air in an external pipe, causing it to rise to the top of the silo, carrying phosphine from a fumigation box at the base of the silo
- Dr Greg Doran
Dr Doran said he and Dr Stevens are examining how this fumigation technology will perform under a variety of climatic conditions.
Testing the latest system for insect control
Research, conducted in collaboration by Dr Greg Doran at Charles Sturt University, Wagga Wagga (CSU) and NSW DPI research scientist Dr Mark Stevens into the efficiency of thermo-siphoning fumigation in silos is supported by an innovation connections grand under the auspices of the Federal government’s Entrepreneurs’ Programme, in partnership with HE Silos based at Forbes.
The researchers are using a HE silo sited within the research facility at CSU, Wagga Wagga which has been fitted with sensors through which variations in temperature, humidity, dispersal and the concentration of the phosphine gas through a number of experiments during the following twelve months.
“We aim to test the parameters of this fumigation technology to provide information to the silo manifacturesr and the grain growers who may use the technology,” Dr Doran said.
In order to kill grain pests at all stages of their life cycle (egg, larva, pupa, adult), including pests with strong resistance, Grains Research and Development Corporation (GRDC) recommends phosphine gas concentration levels need to reach and be maintained at 300 parts per million (ppm) for seven days (when grain is above 25°C) or 200ppm for 10 days (between 15–25°C).
Phosphine remains the single-most relied upon fumigant to control stored grain pests in Australian grain-production systems, but continued misuse is resulting in poor insect control and developing resistance in key pest species.
Unlike herbicides, where resistance can be avoided by rotating chemical group from year to year, there are few alternative stored grain fumigation options other than phosphine; and the best way to prevent resistance is to use phosphine correctly — in a gas-tight, sealed silo.
