Clean augers, field bins and silos prevent insects contaminating grain
Winter is the best time to do a thorough check and clean out of empty storage and grain handling equipment. During the cooler months of the year grain insect activity is at its lowest, breeding is almost nonexistent and flight does not occur therefore extending the period of protection of any hygiene measures undertaken.
Growers are reminded that they should check and maintain grain silos before storing this year's harvest to enable the use of phosphine for insect disinfestation. Regulations prohibit the sale and handling of insect infested grain as well as the spraying of contact insecticides onto grain which is not going to be used for seed.
Gas-tight sealable silos are the preferred system of storage but rubber seals should be checked. Augers, field bins and silos should be thoroughly cleaned of grain residues and treated with a hygiene spray or dust. The ground around storages should be cleared of weeds and rubbish to prevent harboring insects. Old grain resides should be burned or buried deep.
Be aware of withholding periods if you are treating the inside of an empty silo with a registered insecticide such as fenitrothion, to provide residual control before the grain is loaded. Non-chemical products such as silica dust (e.g. Dryacide®) need at least two weeks before loading grain to be effective.
Dryacide is a naturally occurring insecticide and will provide good control for at least 12 months. It is a non-toxic, diatomaceous earth product that is recommended as a structural treatment.
Nitrogen can be used on its own for effective insect control but requires the silo to be initially purged along with very high levels of silo sealing to maintain an environment free of oxygen.
Nitrogen can also be coupled with other fumigant delivery systems to apply chemicals such as ethyl formate to dramatically reduce fumigation exposure periods.
While a relatively expensive option, the advantages of using nitrogen for managing insects in stored grain are there are no withholding periods, no fumigant residues and no insect-resistance issues.
Growers are reminded that the insecticide fenitrothion is not registered as a seed treatment. Fenitrothion is a contaminant in exported grain. Growers using feniitrothion in the weeks prior to harvest should leave the chemical in place for 2-3 days and then wash it off to prevent contamination of any grain that may come into contact with the sprayed surface. It is better to have applied fenitrothion to an empty silo at least two months before harvest to allow it to degrade to harmless substances.
Phosphine is the cheapest form of insect control at around 40c/tonne but growers need to be sure their silo has ample light hydraulic oil in the pressure relief valve and the silo is sealed.
Phosphine is a very effective fumigant gas for sealed storages but it must be held in a gas-tight sealable silo meeting Australian Standard; AS2628-2010. See the GRDC supported Stored grain information hub website for more details.
This ensures the gas is maintained at a lethal concentration for 7-10 days to kill all insect growth stages. Poor fumigation can result in only adult and larval insects being killed giving the mistaken impression that the fumigation was successful. However, the immature eggs and pupae will not be killed so infestations will likely build up again quickly, selecting for resistant populations. Fumigating in an unsealed silo or field bin is an off label use, it is not only ineffective, at best killing adults and larvae, it will also lead to strong resistance developing on your farm.
Managing phosphine resistance
Insect populations with weak phosphine resistance have developed in all grain-growing states of Australia largely as a result of poor fumigations. Strong resistance is widespread in the eastern states and has started to take hold in the west, so to help minimise the development of strong resistance to phosphine in WA, use well maintained sealed silos.
Detecting phosphine resistant grain pests early will make eradication possible and will protect your income. To arrange a free resistance test for grain pests contact David Cousins, DPIRD stored grain insect group, South Perth on +61 (0)8 9368 3920.
Farmers keeping grain on farm for their own use, with silos that are not sealed can use aeration as an alternative method to keep insects in low numbers.
Aeration cooling is an effective tool which can be used in combination after fumigation for maintaining insect population control. While aeration cooling will not kill insects in WA conditions, it will dramatically reduce reproduction provided aeration fans are used in combination with an aeration controller to selectively push cool dry air through the grain in the silo at a rate of 2-3 litres per second per tonne.
For more information on stored grain management techniques visit;
- GRDC supported website; Stored grain information hub
- GRDC’s Hygiene and structural treatments for grain storage factsheet.
- DPIRD’s Sealed silos make sense page
- DPIRD's Insect pests of stored grain page.
For more information contact David Cousins, Technical Officer, South Perth on +61 (0)8 9368 3920 or Ben White, GRDC Stored Grain on +61 (0)407 941 923.