Canadian Grain Commission
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Protection of farm-stored grains, oilseeds and pulses from insects, mites and moulds

3. Introduction

Protecting stored grain and oilseed crops from spoilage is an essential part of their production; failure to do so may result in their being downgraded. Heated or insect- and mite-infested crops in storage quickly lose weight and quality and may cost individual farmers thousands of dollars in lost income. Storing grains and oilseeds cool and dry in clean, uninfested bins that are weatherproof and well-aerated prevents such losses, maintains quality, and assures saleability.

The small, light-avoiding insect and mite pests of stored crops can penetrate deep into bulk-stored crops. In empty bins, they hide in cracks and crevices where they survive in residues until a newly harvested crop arrives. Most do not attack field crops and are not brought into storage with the grain, although rice weevils and lesser grain borers infest cereals in the field in warm climates. Stored-product pests also feed on dried animal and vegetable matter and on moulds; some survive on food that contains as little as 8% moisture. Cold-hardy insects can survive the winter in stored crops. During summer, some insects fly and can be carried by the wind from infested grain residues and animal feeds to granaries and even into houses.

In Canada, many of the insect and mite pests of stored grain and oilseed crops are cold hardy; these pests manage to survive the winter by finding protected habitats among the seeds or by adaptation to cold, or by changing to a nonfeeding, hardy life stage, as in some mites. Insects rarely reproduce at temperatures below about 17°C and mites below 3°C, but, when stored crops heat up, insects, especially the rusty grain beetle and red flour beetle, multiply rapidly and do much damage. The moisture content of grain also affects the extent to which insects and mites infest stored crops and cause them to heat and spoil. The insects, mites and moulds that cause grains and oilseeds to heat and lose condition are inactive at low temperatures (below about 0°C for moulds). Crops stored in small bins cool more rapidly and evenly during winter than in larger bins that are not aerated. Dry (straight-grade) grain or oilseed crops are less prone to spoilage than tough or damp crops. Tough grains and oilseeds are particularly prone to mite infestation. Canola is often infested by mites and moulds. Canola should be below 8% moisture content for prolonged storage.

Harvested grain or oilseed crops contain small amounts of storage moulds (storage fungi) that develop during storage and cause spoilage. Moulds develop rapidly in crops that are stored either tough or damp during warm weather (Table 1). Under warm, moist harvest and storage conditions, some fungi may produce poisonous mycotoxins.

Stored grain or oilseed problems are best understood when bulk grain is considered as an ecosystem in which living organisms (e.g., grains, insects, mites and moulds) and their nonliving environment (e.g., temperature, moisture and oxygen) interact with one another. Grain quality usually declines slowly, but when certain conditions occur in undisturbed bulks, spoilage is faster; complete loss of the crop quality may follow.