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It’s not over yet… plan for stored grain insects

Now that harvest is approaching or underway in many regions, it is timely to consider how to best manage grain quality post-harvest

The lesser grain borer is one of several high-risk pests of stored grain (Source: GRDC).


Harvested grain is at its highest quality when first loaded into storage. If the storage environment is not managed correctly, the quality will steadily deteriorate. Grain storage expert, Peter Botta (PCB Consulting), stresses that three key factors can provide significant benefits for both grain quality and control of storage pests: (i) farm hygiene, (ii) aeration cooling, and (iii) storage choice. There is a nil tolerance for live storage pests in grain sold off-farm.

Critical issues in the management of stored grain pests

There are many damaging insect pests of stored grain and phosphine fumigation is one of the most commonly used techniques for protecting grain. Unfortunately the widespread use of phosphine has lead to the development of resistance in several insect pests of stored grain, including the lesser grain borer (Rhyzopertha dominica), the saw toothed grain beetle (Oryzaephilus surinamensis), the flat grain beetle (Cryptolestes spp.) and the rust red flour beetle (Tribolium castaneum). There are many other beetles, moths and mites that can also be pests of stored grain. Correct insect identification will allow for more targeted control options, and minimise the likelihood of control failures due to resistance.

Good hygiene is a critical factor in the management of stored grain pests. Grain residues in or around storages, or older grain stocks held over from last season provide ideal breeding sites for insects. As little as one bag of infested grain can produce more than one million insects during a year, which can travel to other grain storages where they will start new infestations. Successful grain hygiene involves the removal of all waste grain from storages and equipment including headers, augers, storage facilities and old grain bags.


The best approach to manage chemical resistance is to ensure phosphine is only used when necessary and fumigation takes place in gas-tight storages. Phosphine should be held at lethal concentrations for 7-10 days to ensure effective control of all insect life stages.

Regulations prohibit the sale and handling of insect-infested grain and the spraying of contact insecticides onto grain, other than malathion.

Our advice

We recommend the following steps to minimise problems that can reduce grain quality in storage:

• Clean up grain residues and spillages in and around empty storage facilities and machinery, and remove weeds and rubbish.

• Augers, field bins and silos should be thoroughly cleaned of grain residues and treated with a hygiene spray or dust.

• Ensure insect pests are not carried onto your property on farm machinery.

• Silos that will be fumigated should have their seals checked prior to filling to ensure they are gas-tight.

• Consider installing aeration cooling fans and aeration controllers.

• Monitor stored grain monthly for insects, grain temperature and moisture.

• Be aware of withholding periods if you are treating the inside of an empty silo with a registered insecticide.

• Grain that is to be stored for more than 6 weeks should be treated with an insecticide.


Further information

For further information on grain storage pests, including identification, monitoring and management refer to GRDC Grain Storage Fact Sheet: Stored Grain Pests Identification or the GRDC Grain storage facilities booklet,, or ring 1800WEEVIL to speak to an expert.

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