Temporary grain storages store approximately 60% of Australia’s grain. This temporary grain storage system is an inexpensive alternative way to the traditional permanent storage system.
Metal wall temporary storage is the most common form of temporary storage followed by concrete wall. In emergency situations dirt bunkers are also used on higher ground site for very short periods.
The loss of grain is greater in temporary storage due to leaking tarpaulins caused by birds eating holes in them and higher risk of ground flooding. More fumigate is also require during fumigation period as the sealing of the tarpaulin to the floor and wall is always an issue.
Fumigating an unsealed bunker does not kill pests at all stages of their life cycle. Repeat fumigations in unsealed bunker 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 unsealed bunker that are not 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.