Insects and Mould in Stored Grain

Insect Control – Prevention

Clean Storage Facilities

Storage and transport facilities should be cleaned thoroughly and sprayed or dusted, if needed, with a recommended insecticide before storing grain in the bin (e.g. malathion, diatomaceous earth or cyfluthrin – refer to product labels for details). Clean storage will eliminate one source of infestation. However, grain stored for long periods of time still has the potential for renewed infestations.

Dry and Cool Grain

Ideally, the grain should be dry before being put into storage, and cooled as quickly as possible. For long-term storage, producers are urged to lower the grain temperature below 15°C as soon as possible after the grain is placed in storage. At 15°C, insects in the stored product stop laying eggs and developing. Aeration systems used during the night immediately after harvest should have the grain below 15°C in about two weeks. Grain that is not moved or aerated after harvest can remain warm enough to allow insects to survive the winter. Convection currents arising from this warm air can also promote condensation, sprouting (heating) and mould growth in unmanaged grain. These conditions are very attractive to stored product pests and support their development.

Monitoring for Insects

Regular monitoring of the stored grain is the next step in determining the presence and potential for serious infestations. Either the presence of insects or damaged kernels will give an indication of a problem. Probably the most sensitive means of detecting insects in stored grain is through the use of probe traps, available from numerous crop protection agents. Often the first indication of an infestation will be found near the top centre of a storage bin, and therefore, this is where traps should be placed. Monitoring should take place once every seven to 10 days during the onset of storage (first 60 days) and then the frequency of monitoring may be adjusted.

Identifying insects in stored grain

Correct identification of insects found in stored grain is important in determining the most appropriate control methods. Some of the insects found in stored grain feed on the grain, while others feed on fungus that may be developing in the stored grain.

Grain feeders

Insects that feed on the grain include rusty grain beetles, red flour beetles, and saw-toothed grain beetles.

• The rusty grain beetle is the most common stored product insect. Heavy infestations of this insect cause grain to heat and spoil.
• The red flour beetle is the other common insect pest of stored grain in the prairies. Red flour beetles cannot feed on undamaged, dry seed with less than 12 per cent moisture content. They prefer grain dust, broken grain and milled stocks. Red flour beetles can be controlled by moving grain, whether or not it is cold.
• Saw-toothed grain beetles are more common in stored oats than in stored wheat and barley.

Fungus feeders

Insects that feed on fungus in the grain bin include the foreign grain beetle, hairy fungus beetle, psocids and grain mites.

• Foreign grain beetles resemble the rusty grain beetle, but can be distinguished from it by club-shaped antennae. Also, when placed in a glass jar, foreign grain beetles will climb up the sides, while rusty grain beetles cannot. While foreign grain beetles are considered fungus feeders, they will feed on grain if the moisture content is in the high end of the acceptable range (eg. 14.5 per cent moisture content wheat).
• Grain mites are whitish, about 0.2 to 0.5 mm long, and can be hard to see with the naked eye. About eight kinds of mites are common in farm granaries and elevators.
• Psocids are soft-bodied insects, about one mm long, with long antennae relative to the body size.

Fungus feeding insects and mites cannot survive in dry grain. Chemical control is not necessary for fungus feeding pests in stored grain. Practices that result in the grain drying may be all that is needed to control such pests.

Information to help identify insect pests of stored grain can be found at: http://www.grainscanada.gc.ca/storage-entrepose/mqsgm-mgqge-eng.htm

Control Techniques

The Canada Grain Act states there is zero tolerance for any primary insects (those that feed on whole, sound grain) in grain delivered to elevators. Below are some control techniques, showing when and how these techniques can be best used.

Cold Temperatures

Time Required to Kill Insects at Various Grain Temperatures

Rusty grain beetles are cold hardy and can survive subzero temperatures. Rusty grain beetles and other stored grain insects can be killed by reducing core grain temperatures as follows:

Cooling the grain, through aeration or moving the grain several times during mid-winter, should provide effective control of rusty grain beetles.

Moving Grain with Pneumatic Conveyors

Moving the grain using pneumatic conveyors (grain vacs) has also proven to be an effective means of controlling free-living insects in stored grain.

Chemical Control

Phostoxin

Company: Degesch America Inc. (Phostoxin)
Formulation: 55 per cent aluminum phosphide.

• Insects controlled: Rusty grain beetle, red flour beetle, saw-toothed grain beetle, granary weevil, Indian meal moth and yellow mealworm.
• Approved for use on the following stored grains: Barley, corn, dried peas, lentils, oats, rice, rye, soybeans, sunflower seeds, triticale and wheat.
• Restricted Product: The use and sale of Aluminium Phosphide (Phostoxin) is restricted to licensed pesticide applicators possessing a valid fumigation licence (Saskatchewan) or stored agricultural products licence (Manitoba).
• Rate and Minimum Exposure Period: Refer to labels to determine rate. For grain bins, a dosage of 250-500 tablets (or 880-2560 pellets) per 100m³ of bin space being treated (not volume of grain) is recommended. It is important to ensure that bins are relatively secure. It is not advisable to use phosphine products in bins that are leaky or not well sealed.

The following table may be used as a guide to determine the minimum length of exposure period to phostoxin at the indicated temperatures:

If the grain is less than 5°C, then the tablets will not release the gas until the grain temperature warms up. This may result in poor control and accidental exposure to phostoxin at a later date in grain handling facilities. Very dry grain will also slow the release of the gas from the pellets. A shortened exposure period cannot be compensated for by increased dosage. Also ensure that storage is well ventilated for at least 24 hours after the required time for fumigation.

Protect-It, Insecto

Company: Hedley Technologies Inc. (Protect-It) PCP#24259; Natural Insecto Products Inc. (Insecto) PCP#22489
Formulation: 90 per cent Diatomaceous Earth (DE)

• Insects controlled: Rusty grain beetle (Protect-It only), rice weevil, granary weevil, Angoumois grain moth, Mediterranean flour moth, Indian meal moth, red flour beetle and Tribolium.
• Approved for use on the following stored products: Feed grains, seed, stored grains, wheat, barley, buckwheat, corn, oats, rye, flax, peas, soybeans and sorghum. This product is also registered for structural treatment of empty grain storage and transportation containers.
• How it works: Diatomaceous earth damages the cuticle of the insect, reducing the insect's ability to retain moisture. The insect eventually dies from dehydration.
• Rate, for empty storage structures: Use a dust blower or aeration fan to get diatomaceous earth into the cracks, crevices and void spaces of the structure being treated. Dust areas at a rate of one kg per 200 square meters (5 g/m²).
• Rate, while grain is being placed into storage: Protect-It; The application rate for Protect-It varies by crop and insect species, ranging from 100 g/tonne for control of rusty grain beetle in wheat to 1000g/tonne for red flour beetle in corn. Refer to the label for details. Insecto; Apply to grain at the time of storage at a rate of 0.5 to 1 kg per tonne of grain (500-1000 ppm).

Precautions: The application of DE will lower the test weight measurement of the grain, but usually not to the point of downgrading. If test weight loss is excessive, the grain can be diluted with untreated grain. DE is non-toxic to humans and animals.

Malathion Grain Protectant Dust

Company: Interprovincial Co-operative PCP# 17222
Formulation: 2 per cent malathion

• Insects controlled: confused flour beetles, flat grain beetles, granary weevil, Indian meal moth, lesser grain borer, rusty grain beetle and saw-toothed grain beetle.
• Approved for use on the following stored grains: Wheat, rye, barley and oats.

Malathion Grain Protectant can be applied to grain as it is being loaded into a bin or as it is being turned by adding gradually at the grain auger. It can also be used to control surface infestations by applying to the grain surface and raking in to 15 cm depth of the grain. Malathion controls insects by ingestion and contact, and insects must be active for it to be effective.

• Do not apply to grain within seven days of sale.
• Be aware that the Canadian Grain Commission allows only eight ppm of malathion residue in stored grains.

Malathion 500 Emulsifiable Concentrate

Refer to labels for these products for insect and mite control in empty grain bins.

Malathion 500 (IPCO)

Tempo 20 WP

Company: Bayer CropScience PCP# 25673
Formulation: 20 per cent cyfluthrin. Tempo is a group three (pyrethroid) insecticide.

• Application: Tempo can be used to control insects in grain storage facilities, truck beds and other areas where grain is stored before filling these areas with grain. Cleaning of all areas prior to use of Tempo 20 WP insecticide will increase levels of control. See the insecticide label for specific mixing instructions.

Fungus in Stored Grain

Often mould or "fungal" organisms enter stored grains on different foreign materials. They may be present on farm machinery or as spores found on stored seeds. These organisms are more active when seed-moisture contents are high. Accidental wetting of grain may also stimulate these spores to germinate and cause further mould development.

With the introduction of a mould species, numerous other moulds usually develop in succession. Warm temperature and high moisture are two factors that have an effect on this process. The result is that grain quality may diminish due to heating and spoilage, packing or caking effects, poor germination, and production of off-odours.

Some by-products formed by these fungal organisms may be toxic to farm animals and cause other related problems. These mycotoxins are only detectable by lengthy and complex chemical analysis.

Preventing Fungus Growth

Well designed and constructed granaries are required to prevent mould infestations and preserve grain quality during long-term storage. Smaller quantities of grain will cool and dry quicker than larger masses. Also, in bins holding large volumes of grain, moisture may condense at the surface or sides, providing a suitable environment for fungal organisms to develop. So having more, smaller capacity granaries is better than a few larger ones.

Cooling the grain temperature to -8°C will help inactivate mould growth. Aeration can be used to help reduce grain temperature. You should start the fans when grain is placed in the bin, allowing the grain to cool to the equivalent of outside night temperatures.

At 0°C there may be some efficiency if airflow is reversed. In this case the outside air is chilling the grain, but not removing moisture. In this circumstance, this may reduce the chance for moisture condensation to occur near the top centre of the grain mass.

- Insects, mites, and moulds in farm-stored grain in the Prairie Provinces, Agriculture Canada, Publication 1595/E, Revised 1983
- Annual Guide to Crop Protection Saskatchewan, Saskatchewan Ministry of Agriculture