Clean augers, field bins and silos prevent insects contaminating grain
The 2017 harvest has commenced in WA with the CBH Group tweeting that the first load of canola had been delivered at Esperance on Friday 6 October.
Growers who are yet to commence harvest are reminded that they should check and maintain grain silos before storing this year's harvest to guard against grain storage pests. Regulations prohibit the sale and handling of insect infested grain as well as the spraying of contact insecticides onto grain. The exception is malathion which can be sprayed onto stored grain.
Sealed 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 deep buried.
Be aware of withholding periods if you are treating the inside of an empty silo with a suitable insecticide such as malathion or fenitrothion, to provide residual control before the grain is loaded. Non-chemical products like Dryacide® dust need at least two weeks to be effective.
Dryacide is an insecticide and will provide good control for at least 12 months. It is a non-toxic, diatomaceous earth product that must be applied when loading the silo at a rate of one kilogram per tonne. This grain can only be used on your own farm since most central grain buyers will not accept it as it changes the flow characteristic of the grain. However you can store grain even in an open shed very safely using Dryacide.
Fenitrothion is a contaminant in exported grain. If you are using either liquid or dust in the weeks prior to harvest it is recommended you leave it 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 a very effective fumigant gas for sealed storages but it must be held under gas-tight conditions 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, and will 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 or Dryacide or a combination of both as alternative methods to keep insects in low numbers.
Aeration is a tool for creating a low temperature in the silo so that insects breed very slowly. Insects rely on the environmental temperature for body warmth and breed faster in warm conditions. If the temperature is kept below 20°C they will produce less progeny in the storage period. However to stop reproduction, grain temperatures must be kept below 14°C; temperatures below 10°C (difficult in WA) will eventually kill the insects. Failure to follow these strategies may result in the grain having populations of insects and cannot be sold off-farm without fumigation by transferring it to a fully sealed and tested silo.
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.