Application of insecticides directly to grain to prevent infestation may be warranted if grain is to be stored for more than 3 to 6 weeks at grain temperatures above 60° to 70°F. Summer- harvested grains that will be stored 1 month or longer and fall-harvested grains that will remain in storage beyond May or June of the year after harvest should be treated with a protectant insecticide.
Incorporating a surface treatment is adequate for short-term protection. However, uniform application to all grain at the auger is necessary for long-term protection.
If grain- protectant insecticides are applied at labeled rates, grain may be processed or fed to livestock with no waiting period.
To protect against stored-grain beetles and weevils throughout the entire mass of grain within a bin, apply a protectant insecticide to grain as it is augered into the bin. Spray-on applicators may be mounted on the auger to apply liquid formulations.
Dusts may be spread over a load of grain in a truck or wagon just before unloading.
Protectant insecticides should not be applied to grain before high-temperature drying. A “topdress” or “cap-off” treatment may be used to give some control of insects entering the top of the grain mass. If stirrators are used after a topdress application, the surface of the grain mass will no longer be protected.
Table 1 summarizes the uses for registered grain protectants. Cropspecific recommendations for the use of protectant insecticides are described in the subsequent sections.
Corn:
It is not necessary to apply any insecticide to new crop corn that will be removed from storage by May or June of the following spring. Similarly, if corn will be used on-site as livestock feed (and not subject to grading associated with sale) within 1 year of harvest, a protectant insecticide usually is not necessary.
For storage periods of 1 year or longer, apply Actellic at the loading auger, using rates listed in Table 1. Reldan is not registered for use on corn. Do not apply insecticides before high-temperature drying because extreme heat results in rapid volatilization of the insecticide and reduction in residues.
For Actellic residues to persist on corn at effective levels through the summer after harvest, corn must be dried to approximately 14 to 15 percent moisture. If the grain mass is not treated, surface topdressing or cap-off applications of protectant insecticides are effective against insects that feed at the grain surface.
Actellic, Bacillus thuringiensis (Bt), Diacon II, and diatomaceous earth may be applied to corn and incorporated into the top 4 to 6 inches of the grain mass by raking. Actellic, Diacon II, and diatomaceous earth are labeled for use against all the insects that infest stored grain; Bt products are effective against Indianmeal moth larvae.
Dichlorvos resin strips may be hung in the bin headspace as a further deterrent to Indianmeal moth infestation. See the text starting in the next column regarding Diacon II and diatomaceous earth.
Long-term storage programs usually allow “rotating” corn in storage—shipping out old corn and replacing it with the new crop each year. Annual rotation of stored corn helps avoid buildup of insect infestations. Where annual rotation is practiced, topdress treatments of Bt (for Indianmeal moth) or Actellic applied in April or May usually provide adequate control without treating the entire grain mass.
Soybean:
Only the Indianmeal moth infests soybean stored at moisture levels that prevent mold growth. To protect against Indianmeal moth infestation, rake in surface applications of Bt or diatomaceous earth after the bin is filled and leveled or by May of the following year.
Dichlorvos resin strips may be hung in the bin head space as a further deterrent to Indianmeal moth infestation. No other protectant insecticides are registered for application to stored soybean.
Wheat:
Wheat is especially vulnerable to insect infestation because it is harvested in midsummer when stored- product insects are active within and outside storage facilities. Warm temperatures in summer-harvested wheat also contribute to the rapid development and reproduction of insects within bins. Apply Storcide II at the loading auger to all wheat that is to be stored for 1 month or more.
Sorghum:
For storage periods of 1 year or longer, apply Actellic or Storcide II at the loading auger, but not before high-temperature drying. Actellic should persist for 12 months or more on sorghum at 12 to 13 percent moisture.
Use dichlorvos resin strips or rake in surface applications of Bt or diatomaceous earth after the bin is filled and leveled or by May to control Indianmeal moth if the grain mass is not otherwise treated.
Topdress applications of Actellic usually will provide adequate protection for one summer’s storage if application is made by April or May.
Insecticide Resistance in Stored Grain:
Insecticide resistance is an important worldwide problem that is especially common (on an international scale) in stored-product insects. In Illinois, resistance to malathion is widespread among Indianmeal moth populations.
Some Illinois populations of the red flour beetle are resistant to malathion, but the range and intensity of this resistance problem are not well known. Populations of the hairy fungus beetle may be resistant to both Actellic and malathion; the geographical range of resistant populations of this species is not known.
Diacon II and Diatomaceous Earth:
Diacon II contains the insect-growth regulator methoprene. It prevents the normal growth and maturation of immature insects, killing them before they become adults. It does not kill adult insects and, therefore, may not be as effective as needed in many circumstances.
Diatomaceous earth is an abrasive and slightly sorptive dust that damages an insect’s body covering and causes death by dehydration. Incorporating surface treatments should provide some control of insects active in the treated layer.
Problems associated with the use of diatomaceous earth as a grain protectant throughout a grain mass include increased wear to grain-moving equipment, the generation of great amounts of airborne dust during grain handling, and possible reductions in test weight.
In addition, diatomaceous earth is not very effective when the grain is wet. Grain that is identified as having been treated with diatomaceous earth is not downgraded when inspected by official grain graders, but some buyers refuse to accept grain treated with diatomaceous earth if the appearance of the grain is altered by a dusty coating.
Conversely, buyers of organic foods or feeds accept grains treated with diatomaceous earth or Bacillus thuringiensis, but not grains treated with synthetic chemical insecticides.
Due to its cost and the drawbacks discussed, using diatomaceous earth to treat an entire grain mass by admixture at the auger, conveyor belt, or bucket elevator is not advised except in unique circumstances, such as the long-term storage of organically certified grains. For topdress applications, diatomaceous earth gives satisfactory results.
Another successful and practical use of diatomaceous earth has been its addition to small seed packets to prevent infestation by stored-product pests.
Authors:
Rick Weinzierl : Department of Crop Sciences
Russell Higgins : Matteson Extension Center
