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

7. Controlling infestations

To keep infestations from spreading to other granaries, pests should be controlled as soon as they are discovered. The type of control implemented will depend on the condition of the grain, bulk temperature, kinds of insects or mites present, and the time of year.

Cooling and cleaning the product

An effective method to control insect infestations in winter is to lower the grain temperature. This can be done by mixing and transferring infested crops from one granary to another which will lower grain temperatures about 10°C in the winter; or by transferring part of the crop to a truck or small pile exposed to low air temperature, leaving it to cool for one or more days and then returning it to the granary. However, aeration systems are much more effective at lowering the grain temperature. Insects do not develop or feed at temperatures below 10°C. At temperatures below 0°C, the insects will die eventually. Control of the rusty grain beetle will be obtained:

  • after 1 week at a grain temperature of -20°C
  • after 4 weeks at a grain temperature of -15°C
  • after 8 weeks at a grain temperature of -10°C
  • after 12 weeks at a grain temperature of -5°C

Because the rusty grain beetle is the species most resistant to low temperature, most other insects in stored grains and oilseeds will also be controlled by these combinations of temperature and exposure periods. The low temperatures listed here do not kill fungi or all mites.

Cleaning the grain also checks infestations. To control surface infestation of moths, mites and spider beetles, remove and destroy webbed and infested patches, rake the bulk surface to break up any crust, and then dry the bulk.

Pneumatic grain-handling equipment

Most free-living adult and larvae insect pests are killed during bin unloading by using a “grain-vac.” Insects are killed by abrasive contact and impact as the grain and insects are moved through the discharge tube. Better control is achieved when there is a 90° bend in the tube; this causes more contact of insects with the sidewalls of the tube.

Diatomaceous earth

Control of rusty grain beetle can be achieved by using a nontoxic dust made from prehistoric diatoms. When rusty grain beetles come in contact with this dust, the waxy covering on their skin is absorbed, leaving them prone to dehydration and death. The product is applied to grain as it is augered into the bin, and is most effective when applied to dry grain at harvest. Control can take up to five or six weeks.

Treating with insecticides


Resistance to insecticides (notably malathion) is becoming more common in stored-product insects across Canada notably in the Indianmeal moth in central Canada and in the red flour beetle, confused flour beetle and rusty grain beetle throughout most of the country. Repeated use of one kind of insecticide in the same storage area increases the chance of development of insecticide resistance on the part of an insect pest. Use more than one control and prevention method, and use an insecticide only when it is absolutely necessary.

To control insects occurring in residues in empty granaries, use only an insecticide that has been approved for use in granaries, and take precautions in its handling and use. Approved insecticides are selected largely on the basis of the following:

  • low toxicity to mammals and high toxicity to insects
  • freedom from taint or odour on food
  • non persistent environmental effects
  • safe, economical and easy use
  • presence of negligible residues or toxic products in food

Some insecticides are more effective and longer lasting than others. Premium-grade malathion, cyfluthrin, pyrethrum with piperonyl butoxide and diatomaceous earth are at present the insecticides registered for empty-bin treatments. Long-term protection of stored cereal can be achieved by adding premium malathion or diatomaceous earth.

As insecticide sprays and dusts act only on contact with insects and do not penetrate piles of grain or dust on floors, remove residues from the granary before applying the insecticide.

Dissolve emulsifiable concentrates of malathion in clean water to form a milky emulsion and spray it on metal and wood surfaces immediately after mixing to avoid the insecticide separating from the water. Emulsifiable concentrates break down rapidly on concrete, but are effective for up to a year on wood or steel. Do not use these sprays near electrical switches or fuse boxes.

Wettable powder sprays can be applied to concrete, brick, metal or wood surfaces (Fig. 13B). Mix wettable powder formulations of malathion with clean water in a separate container before filling the sprayer. Wettable powders applied on painted surfaces leave white specks.

In cold weather, oil solutions of insecticides are better than water-based sprays because they will not freeze. Oil solutions can be prepared by mixing insecticide in deodourized kerosene following label instructions and can be used near electrical switches. Wood or metal surfaces can be sprayed and empty bins fogged, but avoid treating plastic or rubber surfaces with oil solutions.

Insects beneath the floor or within wall spaces may be controlled with insecticide powders or dusts, because these places are hard to treat with liquid insecticides. These powders or dusts are usually commercial formulations of malathion on treated wheat flour. Use a dust applicator or sweep the dust into cracks in the floor.

Oilseeds absorb contact insecticides from treated granary surfaces. Therefore, avoid treating granaries in which oilseeds are to be stored. If the granary is infested, sweep it well, destroy the sweepings, and treat sparingly only the junctions of the floor and walls.

If stored-product insects are visible on the outside wall of the granary, spray the walls and surrounding ground. Even if insects are not readily visible, it is a sound practice to spray not only grain spillage, but also the ground around the granary and underneath raised granaries.

Application of fumigant tablets to grain

Fig. 13A – Application of fumigant tablets to grain

Application of contact insecticide to an empty granary

Fig. 13B – Application of contact insecticide to an empty granary. Note use of full-face gas mask, rubber gloves, coveralls and hard hat.

Cautions for spray operators

  • Read insecticide labels and follow instructions on them.
  • Examine the sprayer and hoses for leaks.
  • Avoid spillage of insecticide.
  • Use a protective mask with approved filters when applying insecticide in enclosed areas such as empty granaries.
  • Wear protective clothing, hard hat, goggles, rubber work boots and rubber gloves during preparation and spraying.

Use of concentrates

The amount of water needed to dilute emulsifiable concentrates or wettable powder formulations depends on the amount of insecticide in the concentrate and the dosage of insecticide recommended to control the pest. Use the following example to calculate how much water to add to a 50% emulsifiable concentrate to obtain a 1% spray solution of malathion.

(50 - 1)/1 = 49/1 = 49

Therefore, add 1 part (0.1 L) of a 50% emulsion to 49 parts (4.9 L) of water to obtain a 1% spray.

Use a 1% spray of malathion to control rusty grain beetles in empty farm granaries. Apply the spray evenly with a portable compressed-air sprayer at 5 L/100 m² using a nozzle with a 0.4-mm diameter orifice for emulsifiable concentrates or oil solutions and a 0.8-1.2-mm diameter orifice for wettable powder solutions.

Grain treatment

Grain treatment is not a substitute for good housekeeping; however, special formulations of premium-grade malathion are available for treating cereals for long-term (8 months to 1 year) protection from insects. Either liquid insecticide is sprayed on the grain, or dust composed of treated wheat flour is mixed with the grain at rates that are dependent on its flow through the auger.

Follow the instructions on the label

Chemical odours will be produced that lower the selling price of grain if insecticides are applied at rates in excess of those recommended. Insecticide-treated grain should neither be sold for 7 days nor used for feed for 60 days after treatment.

To treat the grain with a 1% spray of premium-grade malathion, apply it at 0.8 L/t of wheat. Use Table 5 to determine the amount and rate of malathion for application. The treatment is effective as a protectant, but the grain should be stored in good condition and contain less than 14% moisture, otherwise the insecticide will break down quickly, reducing its residual activity.

Table 5 – Amount and rate of premium-grade malathion required for application ¹
Flow rate (wheat) Application rate (1% spray)
t/h t/min L/h L/min
¹ The Canadian Grain Commission does not recommend the use of grain protectants for the following reasons:
  • insect problems may not arise
  • alternative control measures, such as aeration or grain movement, are available
  • chemical residues remain in the grain.
3 0.05 2.4 0.04
6 0.10 4.8 0.08
9 0.15 7.2 0.12
12 0.20 9.6 0.16
15 0.25 12.0 0.20


Fumigants generate toxic gases that are used to control insects in stored grain. They are available for farm use only as solid formulations. Fumigants are also toxic to humans and farm animals and, therefore, must be applied only by trained people. Avoid inhaling the vapours, and follow the directions on the container (see section on “Cautions for fumigators”). CO2 is registered for fumigation of grain, but bins must be made airtight; welded steel hopper bins can be made airtight for about $300.00 and the cost of fumigation with dry ice (CO2) is comparable to phosphine treatment, only slower.

The solid fumigant aluminum phosphide, which generates phosphine gas in the presence of air moisture, should be applied only when the following conditions are met:

  • Licensed personnel must apply fumigants.
  • The grain temperature is at least 10°C. Fumigants are most effective at temperatures higher than 20°C. If the grain is below 5°C do not fumigate. Cool the grain to decrease the severity of the infestation by moving it to another bin or by aerating.
  • The infested grain is stored in a granary that can be tightly sealed to retain the gas for at least 5 days by plugging cracks, crevices and other openings.
  • Rapid control of an infestation is needed before selling the grain.
  • Full-face gas masks in good condition and with the appropriate canister for phosphine, cotton gloves and protective clothing are available to wear during application.
  • Gas-detector tubes or other detection equipment are available.


In calculating fumigant dosage on the basis of bin volume, include the headspace above the grain. Use correct number of tablets or pellets as recommended by the manufacturer. Add tablets or pellets of solid fumigant (aluminum or magnesium phosphide) either to the grain stream as it is discharged from an auger into a sealed bin or by probing them into the grain at regular intervals once the bin is filled. Treat small bins of about 27-tonne capacity by dropping the fumigant through metal pipes inserted into the grain (Fig. 13A). Select about 12 evenly spaced points on the surface of the grain and mark them with wooden stakes. Insert a pipe 3-cm in diameter and 1.5 m long at each point and drop a tablet into the grain every 15 cm as the pipe is withdrawn. Start at the far end of the bin and work towards the door. Push some tablets into the auger hole before sealing.

In bins that cannot be tightly sealed at the top, cover the grain with polyethylene sheeting to reduce loss of fumigant and to improve effectiveness of treatment.

Cautions for fumigators

When using fumigants, follow the directions on the label closely and especially take the following precautions:

  • Always wear a full-face gas mask either when applying fumigant to binned grain, to grain during augering or when entering a fumigated bin. Respirators are ineffective on bearded men because a tight seal cannot be made around the face.
  • Always fit a new canister in your mask before starting fumigation. Use the type of canister recommended for phosphine gas. A canister does not protect people exposed to heavy concentrations inside buildings (for gas levels above 2% in air) and does not supply oxygen.
  • Always work with at least one other person.
  • Wear dry gloves of cotton or other breathable material. Aerate used gloves and other contaminated clothing in a well ventilated area before laundering.
  • Wear coveralls and a hard hat.
  • If an individual shows symptoms of overexposure to a fumigant, move that person to fresh air and call a doctor immediately. Symptoms of fumigant poisoning are dizziness, blurring vision, vomiting and abdominal pain.
  • After applying the fumigant to a granary, nail or lock the doors, seal ventilators, and post warning signs on the door.
  • Fumigated areas must be aerated to 0.3 ppm hydrogen phosphide or less prior to re-entry by unprotected workers. Because fumigated grain can take several weeks to aerate during cold weather, check for residual gas with gas detector tubes from outside the bin before entry and inside during any prolonged period of work in the bin.
  • Do not feed fumigated grain to livestock unless the grain has been shown to be gas free by detector tubes or other analyses.
  • Always consider wind direction. If there is a dwelling or livestock close to and downwind from the structure to be fumigated, postpone fumigation until the wind subsides or changes direction.
  • Do not fumigate when winds are strong.
  • For your safety, position yourself upwind during application of fumigant to grain being augered into a bin. Avoid standing downwind from a bin under fumigation.
  • Phosphine gas may react with certain metals, especially copper, brass, silver and gold to cause corrosion at high temperatures and humidity. Take precautions to remove or protect equipment containing these metals, such as electric motors, wiring and electronic systems.