Australian farmers grow $8 to $10 billion dollars of grain per year and now are holding an increasing amount of grain on-farm for extended periods before sale or consumption by livestock. Deregulation of the domestic grain market and increasing production of “non-traditional” grain corps as alternatives to cereal grains such as wheat, barley and oats are key factors driving the move to greater on farm storage.
Fumigating with phosphine in unsealed silos does not kill pests at all stages of their life cycle. Repeat fumigations in unsealed silos increases resistance levels and selects for insects with a higher phosphine tolerance. In order to kill grain pests at all stages of their cycle (eggs, larvae, pupae, adult), phosphine gas concentration levels need to reach and remain at 300 parts per million (ppm) for seven days or 200ppm for 10 days. Trials show that these levels of gas concentration are impossible to achieve in silos that are not pressure tested and sealed gas-tight, so insects will not be killed at all life stages. The fumigation may appear successful when the adults die but the surviving eggs and pupae will continue to develop and reinfest the grain.
Technically, a farm silo is only truly sealed if it passes a five-minute half-life pressure test according to the new Australian Standards AS2628. Often silos are sold as sealed but are not gas-tight, rendering them unsuitable for fumigation.