Stored grain insects

Given that harvest is now underway it is timely to consider how to best manage grain quality post-harvest. Harvested grain is at its highest quality when it is first loaded into storage. If the storage environment is not managed correctly, then quality will steadily deteriorate. Grain storage expert, Peter Botta (PCB Consulting), says three key factors (farm hygiene, aeration cooling and storage choice) can provide significant gains for both grain quality and control of storage 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 common insect pests of stored grain: 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). The best approach to manage this resistance is to ensure phosphine is only used when absolutely necessary and that fumigation only takes place in airtight storages. Phosphine should be held at lethal concentrations for 7-10 days to ensure effective control of all insect life stages. Poor fumigation practices will worsen the resistance problem by selecting for resistance.

The following steps are recommended in order to minimise problems that can reduce grain quality in storage:

• Clean up grain residues and spillages in and around empty storage facilities and machinery used for grain handling before processing this season’s grain.
• Ensure insect pests are not carried onto your property on farm machinery such as harvesters. All equipment should be thoroughly cleaned down after use. The first grain through the header is often at the greatest risk of early infection.
• Storages and equipment can be treated with an inert dust treatment once they have been cleaned.
• Silos that will be fumigated should have their seals checked prior to filling to ensure they are gas-tight. Grain that is to be stored for more than 6 weeks should generally be treated with an insecticide.
• Aeration controllers can be used to rapidly reduce stored grain temperatures, which will help to limit the activity of insects and avoid grain spoilage from moulds and fungi.