Current Stored Grain Insecticide Options

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Glenn F. Chappell II, Extension Agent; Wade E. Thomason, Extension Grains Specialist

Managing stored grains requires the use of various techniques to ensure that the quality of the grain entering the storage facility does not deteriorate over time. Relatively few insecticides are currently labeled for use in or on stored grain; however, insecticides are only one option in an arsenal of strategies used to protect our stored commodities. In addition to the judicious use of insecticides, the following measures should be included in a complete program: the use of sanitation; storing sound, dry grain; managing temperature and aeration; and regular sampling. Bin facilities also play an important role in determining whether grain quality is maintained and should be inspected regularly for deterioration of any type. Four insecticide treatment options in stored grain include applying insecticides as an empty-bin spray, treating the entire grain mass (protectants), treating the top of the grain mass (top-dress treatment), and fumigation.

Empty-bin sprays are recommended when grain is stored in the summer, if there are difficult to clean areas or if there has been a history of insect problems. After bins have been properly cleaned and inspected and prior to adding new grain, treat the empty bin with a labeled insecticide. Spray to run-off the inside surface and as much of the outside, including the nearby ground surfaces, aeration ducts, and grain handling equipment, as possible. Sprays should be concentrated on cracks, crevices, and hard to clean areas. Applications should be made at least two weeks prior to adding new grain. Allow 24 hours for sprays to dry. These sprays provide a barrier to insects that may be attracted to the storage facilities and also provide control of the insects not removed during the cleaning operation.

Storcide II (chlorpyrifos-methyl + deltamethrin), Storcide (chlorpyrifos-methyl + cyfluthrin), Tempo (cyfluthrin), Malathion (various products), Reldan 4E (chlorpyrifos-methyl), Diacon II [(s)-methoprene], Silicon dioxide and/or diatomaceous earth (DE) (Insecto, Perma-Guard, and others), and Bacillus thuringiensis (Bt) (Dipel, Biobit), are all labeled as empty-bin sprays. Refer to the individual product label for a list of the insects controlled.

A grain protectant may be added to the grain when the bin is being filled to guard against insect damage. Protectants may also be added to the upper surface of the grain in the bin (top dressing) to protect against damage from moths and other insects entering the top of the storage facility. Protectants are recommended if grain is going to be stored for extended periods, in flat structures, under circumstances that favor pest development, or in facilities with a history of insect damage. Protectants will not eliminate existing infestations and should only be applied to clean, dry grain. The combination of high grain moisture and high temperatures will shorten the residual life of grain protectants.

Storcide II (chlorpyrifos-methyl + deltamethrin) is registered for use on small grains (barley, oats, rice, sorghum and wheat). Storcide II is targeted as the replacement product for Reldan 4E and the original Storcide. It is effective against a broad spectrum of stored grain pests, including lesser grain borer.

Reldan 4E (chlorpyrifos-methyl) is labeled for use on barley, oats, rice, grain sorghum and wheat but is not labeled on corn. Reldan does not have activity on lesser grain borer and has limited activity on existing populations of insects. Distributors will sell Reldan 4E until 12/31/05 and treated grain will be given the opportunity to move through grain channels until 2008-2009.

Diacon II [(s)-methoprene] is registered for use on corn, barley, oats, rice, peanuts, grain sorghum, peanuts, sunflowers, wheat and all food commodities. Diacon II is an insect growth regulator (IGR) that prevents insects from completing their growth and development. Diacon II is not an adulticide. Consult the product label for a list of insects controlled.

Acetellic 5E (pirimiphos-methyl) is registered for use on corn and grain sorghum. Actellic is also available in a low odor formulation. Do not apply to grain before high temperature drying. Actellic applied at the highest labeled rate will suppress lesser grain borer.

Silicon dioxide and/or diatomaceous earth (DE) (Insecto, Perma-Guard, and others) are registered for all grains. Applications of these materials to the entire grain mass can lower test weight and reduce the flowability of the grain. In many cases, these products are only applied to the bottom and top layers of the grain.

Bacillus thuringiensis (Bt) (Dipel, Biobit) is registered for use on all grains including soybeans. Agitation is important. Read and follow label directions carefully. This product does not control weevils, lesser grain borer, or any bran bugs.

Pyrethrins + piperonyl butoxide (various products) is labeled on corn, wheat, rye, oats, barley, and grain sorghum. These products degrade quickly and provide only short residual control.

6% Malathion Grain Dust (malathion - various products) is labeled for application to wheat, corn, oats, rye, and barley. Only the dust formulation is labeled for direct grain applications! Due to resistance problems with this active ingredient and concerns over residues in flour, malathion is not suggested for direct applications to stored products.

It may be necessary to apply an insecticide to the top few inches of the grain mass (top dressing) to prevent the introduction of insects (primarily moths) through the head space. Top dressings should be applied to the grain as soon as the bin is filled and the surface of the grain mass is leveled. They may need to be reapplied anytime the surface is disturbed. Bacillus thuringiensis (Bt)(Dipel, Biobit, etc.), chlorpyrifos-methyl (Reldan 4E), malathion (6% Malathion Dust), chlorpyrifos-methyl + deltamethrin (Storcide II), methoprene (Diacon II), pirimiphos-methyl (Actellic 5E), pyrethrins + piperonyl butoxide (various products) and silicon dioxide (Insecto, Perma-Guard, and others) applied as a top dress treatment will prevent the introduction of most insects including the most common stored grain insect pest, the Indian meal moth. See product labels for a complete list of the pests controlled. Bacillus thuringiensis (Bt) is registered for use on all grains including soybeans. This product only protects against Lepidopteran insect pests, Indian meal moth and Angoumois grain moth, and only impacts the larval (caterpillar) stage.

Resin strips (dichorvos or DDVP) may also be hung in the air space in the top of the bin to help control adult moths. One strip should be used per 1000 cubic feet of air space and replaced after 3 months. For this treatment to be effective, the top of the bin must be temporarily sealed, including the roof vent. Aeration will disrupt this treatment.

When Bacillus thuringiensis, chlorpyrifos-methyl, methoprene, pirimiphos-methyl, pyrethrins + piperonyl butoxide, and silicon dioxide products are applied according to the product labels, there is no required waiting period for subsequent sale, processing, or feeding of grain. Grain can be used immediately. Refer to Storcide and Storcide II product labels for any sale, processing or feeding restrictions.

Fumigation should be conducted only by trained, experienced, registered applicators. If insects are found above the suggested thresholds, fumigation is suggested. The goal of fumigation is to maintain a toxic concentration of gas long enough to kill the target pest population. The toxic gases penetrate into cracks, crevices, the commodity, and the facility treated. Fumigants provide no residual protection. Fumigants come in several forms and formulations. All label instructions and precautions should be read and carefully followed. Fumigant selection should be based on the following factors: pest susceptibility, volatility, penetrability, corrosiveness, safety, flammability, residues, odors, application method, required equipment, and economics. Two products remain for treating stored products - methyl bromide and phosphine producing materials such as magnesium phosphide and aluminum phosphide.

Mention of a trade name neither constitutes endorsement of the products mentioned nor criticism of similar ones not used or mentioned.