The cheapest and safest method of controlling grain pests is prevention. Consider fumigation only as an emergency treatment. Once grain has become infested with insects, the quickest and most effective way to remedy the problem usually is with a fumigant. All fumigants, however, are hazardous and must be handled with extreme caution. Fumigants are considered restricted-use pesticides, and their container labels all carry the signal word “Danger” and a skull-and-crossbones symbol. Only chloropicrin, aluminum phosphide, and magnesium phosphide are available for use as grain fumigants. As of 1990, fumigation of grain storage facilities requires special certification. Contact your local Penn State Cooperative Extension office or the Pennsylvania Department of Agriculture for details. The use of methyl bromide has also been gradually phased out, and its registration will end in 2005.
Although it is legal to acquire private certification to apply fumigants on the farm, a farmer should consider seriously the hazards associated with fumigation products before attempting to fumigate grain. The most commonly used grain fumigant is phosphine gas produced by aluminum phosphide or magnesium phosphide coming in contact with water. These materials are sold as pellets or tablets that are placed in the grain mass. When they make contact with normal air moisture levels, they slowly begin to liberate the phosphine gas. The amount of time that an applicator has to place these tablets in the grain mass and get out before phosphine levels become toxic depends on moisture and air temperature levels. If a tablet or pellet contacts too much moisture, the reaction to liberate the gas is rapid, resulting in an explosion. This explosion can harm the applicator and set the grain mass on fire.
In addition to this significant hazard, the fumigant is a very small molecule that is only slightly heavier than air. Because of these properties, the gas is hard to contain unless the grain bin is tightly sealed. Phosphine can move through plastic, concrete, wood, and any crack or seam in a metal bin. Because it is heavier than air, it will slowly displace air in low areas and become concentrated if it escapes from the bin. Therefore, any work areas, nearby homes, or livestock shelters near a bin under fumigation can build up concentrations of the gas high enough to kill livestock or humans. It is important to note that in 2010, EPA implemented new restrictions on phosphine fumigants prohibiting their use around residential areas, increasing buffer zones for treatment around nonresidential buildings that could be occupied by people or animals, and creating more protective product labeling. Properly handling and using fumigants requires considerable experience. Novices can easily harm themselves, employees, family members, and livestock. For this reason, fumigation is best left in the hands of experienced professionals.
For those who choose to use fumigants, the methods of application, dosages, temperature, moisture, exposure periods, and all precautions are listed on the label. Be certain to read and understand all directions before using any fumigant. In addition, consider the following recommendations:
- Fumigants generally are not fully effective at temperatures below 60°F.
- Aluminum phosphide is less likely to impair seed viability than are other fumigants.
- Aluminum phosphide and magnesium phosphide are extremely corrosive to gold and copper. As a result, electrical and computer circuitry will be damaged if it contacts the gas.
- Use of methyl bromide, once a stored-grain fumigant, is no longer legal. This chemical was phased out completely by EPA, effective January 1, 2005.