Prevent Insects in Stored Grain

WINNIPEG - Sep 6/07 - SNS -- Growers need to take steps to protect grain from insect infestations when it's stored on the farm this fall and winter, says the Canadian Grain Commission (CGC)

The CGC's stored products entomologist Blaine Timlick says that this year producers should be aware of insects that have appeared in grain samples sent to the CGC: the lesser grain borer and the minute scavenger beetle.

The lesser grain borer is not as common in stored wheat as the rusty grain beetle or the red flour beetle. It is one of the smallest -- and one of the most destructive beetles infesting grain in North America. Lesser grain borers attack most kinds of stored grains but are especially damaging to wheat, rice and corn. Both adult and larval stages cause damage.

Not considered a problem pest in Canada, the lesser grain borer has been detected on the Prairies this year. There are indications that its distribution is expanding. The insects are not likely to survive a prairie winter in the wild. In stored grain, however, their ability to survive increases.

The insects bore into the kernels to feed, leaving behind a fine powder and particles of feces. They typically consume 17 to 20 percent of each kernel they damage. The rusty grain beetle, by comparison, consumes only four percent of the kernel.

Timlick says the lesser grain borer possibly was carried on southerly jet streams or was present in grain deliveries from the United States.

Another insect, the minute scavenger beetle, has been detected this year in canola samples. The minute scavenger beetle is small, and its colouring is similar to that of the rusty grain beetle. It thrives in hot and damp weather on swathed canola where it feeds on fungi found on canola pods and stems. As long as canola is binned and stored under cool and dry conditions, the beetle will migrate or die and not present problems.

To prevent infestations of these insects and other types of pests in stored grain, Timlick recommends five steps:

Decide in advance which bin you will use for each crop. The method used for cleaning and preparing an empty bin depends on the crop you plan to store in it. There are many approved chemical insecticides available to treat the interior of empty grain bins used for storing cereal grains. The CGC urges producers not to use chemical insecticides, for example, malathion, on grain bins intended for storing canola and flax because these oilseed crops absorb this type of pesticide, and the residue remains in the seed.

Prepare the bin before filling it. Insects in grain bins feed on debris, dockage and leftover cereal grain. Therefore, clean bins thoroughly. If you plan on storing canola or flax, clean the bin by using high pressure water or air, a heavy broom or vacuum.

Add clean grain to the bin and make it level as possible. Grain is a very good insulator. If warm grain is placed in storage and left undisturbed, convection currents may develop and cause hot spots and condensation. When the grain pile is made level, aeration is more effective.

Bring the temperature down as soon as possible to +15°C. Large amounts of grain stored above 14.5 percent moisture content can develop heated regions. Heat encourages fungal growth. Fungi and heat attract insects in stored grain. Lowering moisture content below 14.5 percent and cooling the grain below +15ºC mitigate insect pest problems in stored product as most stored product pests do not feed or reproduce below +15ºC.

Monitor the temperature of the stored grain and aerate the grain bulk. Check the temperature of the bin every two weeks. Stored grains should be aerated as soon as possible after harvest, particularly if aeration can reduce the bulk temperature below +18°C. When the ambient temperature falls below that of the grain bulk, initially during the early evening, night, and early morning, you can use aeration to reduce the temperature of the grain. Aeration systems preserve stored grain and keep it dry by reducing the temperature of grain and reducing moisture migration.