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Grains storage pests

With many crops now approaching harvest it is timely to think about on farm grain storage issues. Harvested grain is at its highest quality when it is first loaded into storage. If the storage environment is not managed correctly the quality will steadily deteriorate. Grain insects, end-user requirements and maintaining quality are important issues to consider.

Generally, grain to be stored for more than 6 weeks should be treated with an insecticide. Grain can be treated with a protectant when it is added to storage or fumigated in a sealed silo. Most contact insecticides provide between 3-6 months protection, although this is dependent upon the moisture content and temperature of the grain. High moisture content and temperatures can lead to the rapid breakdown of chemicals and leave grain vulnerable to attack. Always aim to store grain at a moisture content of 12% or less and at a temperature of 25°C or less. This will also help to limit the activity of insects and avoid grain spoilage from moulds and fungi.

One of the most important things for growers to understand is the markets they wish to supply and their requirements. This takes careful planning and could mean improving storage facilities. Markets are increasingly demanding grain free of chemical residues. In sealed storage, grain can be fumigated effectively, providing quick, inexpensive and long-lasting insect control without the problem of pesticide residues.

Phosphine fumigation is one of the most commonly used techniques for protecting stored grain from insect pests, with at least 80% of Australian grain fumigated with phosphine each year. Unfortunately the widespread use of phosphine has lead to the development of resistance in four 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).

These pests are all small (between 2-3 mm long) and dark reddish-brown to grey in colour. Check for these species in grain residues in harvesting and grain-handling equipment, and in storages. Strong resistance in these pests has now been detected in populations from all states in eastern Australia. However, this resistance can be managed by ensuring phosphine is only used when absolutely necessary and that fumigation takes place only in airtight storages. Fumigating in unsealed storages will worsen the resistance problem by selecting for resistance.   

Grain handling equipment also requires some routine maintenance in order to minimise the possibility of contributing to grain contamination. Seals on silos should be checked before each filling and replaced if worn or damaged. Headers, carriage equipment (trucks, bins), augers and storages should be thoroughly cleaned down after use. Clean up spillages in areas around silos and destroy all residues to prevent re-infestation.

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