Insecticides to control grain insect pests

Insecticides are a powerful tool to control insect pests. When using any insecticide, read and follow the instructions on the label. This will ensure the safe use of the insecticide for workers and consumers and control of insect pests. Labels for approved insecticides can be found on the web site of Health Canada’s Pest Management Regulatory Agency (PMRA).

Insects can develop resistance to insecticides. Resistance may develop if the same chemical class is used repeatedly. When possible, alternate control methods should be used to minimize the development of resistance.

Residual insecticides for structures

There are several insecticides available for treating cracks and crevices in buildings or empty bins and other storage containers:

  • Malathion
  • Pyrethrins
  • Cyfluthrin
  • Diatomaceous earth
Photo shows a man spraying a chemical insecticide on the interior surface of a steel grain bin
Spraying a chemical insecticide on the interior surface of a steel grain bin

Residual insecticides for direct application to grain

Diatomaceous earth

  • Absorbs waxy layer on insect skin causing death by desiccation of insect.
  • Most effective when applied as dry grain is augered into a bin during harvest.
  • Treatment for a 6-week period at above 20°C is necessary to ensure maximum efficacy.
  • Diatomaceous earth has the potential to reduce test weight. Lower auger flow rates when applying as diatomaceous earth increases grain friction.

Malathion

  • Incapacitates the insect’s central nervous system.
  • Best applied as a liquid spray or dust as grain flows through an auger or conveyer.
  • Intended for use on cereal grains. It is not registered for use on oilseeds.
  • Ensure that the formulation used is registered for direct grain treatment.
  • Not all formulations of malathion meet this registration requirement.
  • Grain treated with malathion should not be sold for 7 days.

Aluminum phosphide (phosphine)

  • Applied as pellets to bulk grain either as the grain is entering storage; or placed into the grain with a probe after the grain is stored; or contained in prepackaged devices (ropes) on grain surface.
  • Structures must be well sealed in order for treatment to be effective.
  • Aluminum phosphide reacts with water in the air to produce the gas phosphine.
  • Grain temperature and moisture are both factors in contributing to the effectiveness of aluminum phosphide. Grain should not be fumigated if the temperature is less than 5oC or if the moisture content is less than 10%.
  • Eggs are the most resistant stage, requiring approximately 20 times higher doses to control than adults and larvae.
  • Phosphine used according to the label will control all life stages and all stored-grain insect pests.
  • Monitoring of phosphine during fumigation will ensure that gas levels are sufficient to control insects.
  • Phosphine may cause corrosion of certain metals (copper, brass, silver and gold) at high temperatures and humidity. Precautions should be taken to remove or protect equipment containing these metals such as electrical motors, wiring and electronic systems.
  • Insect resistance to phosphine is known to occur in the United States and Australia and continuous or inappropriate use may result in resistance developing.
Fumigant pellets are placed into bulk stored grain using a hollow probe
Fumigating stored grain using a probe

Magnesium phosphide (phosphine)

  • Like aluminum phosphide, magnesium phosphide reacts with water in the air to produce the gas phosphine.
  • Magnesium phosphide generates phosphine faster that aluminum phosphide.
  • Unlike aluminum phosphide, magnesium phosphide cannot come in contact with the commodities fumigated.
  • Magnesium phosphide is applied contained in plates, pouches or strips.
  • Mainly used for fumigating empty structures or tarped commodities.
  • Similar issues with temperature, humidity and corrosion of metals as aluminum phosphide.
  • Structures must be well-sealed in order for treatment to be effective.

Gaseous phosphine

  • Gaseous phosphine (compressed gas in a cylinder) allows a more precise dosage of phosphine and faster fumigation than the metal phosphides.
  • Fumigation at minimum temperature of 0°C, compared to metal phosphides with a minimum temperature of 5°C.
  • Similar issues with corrosion of metals as aluminum phosphide.
  • 2 formulations: ECO2FUME® (ready for application), VAPORPH3OS® (needs onsite dilution).

Carbon dioxide

  • Carbon dioxide is applied to grain as a gas from cylinders
  • Structures must be well sealed in order for treatment to be effective
  • Dose: Maintain at 60% for 4 days between 20°C and 25°C. Refer to label for further dose information

Methyl bromide

  • Methyl bromide can be used for quarantine and pre-shipment applications either for export or for import.
  • The only quarantine insect for stored grain is the khapra beetle (Trogoderma granarium).There are several other non-grain pests that are found on wood or other commodities that may need to be fumigated before export or import into Canada.
  • In the past, methyl bromide was used to fumigate flour mills and structures and grain to control stored grain insect pests, but this use has be almost entirely stopped because of restrictions under the Montreal Protocol on Substances that Deplete the Ozone Layer.

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