If a protectant is not used on all incoming grain, it is advisable to apply insecticides to the top 6 to 12 inches of grain. This approach provides an effective barrier against migrating insects such as the Indianmeal moth larvae, which concentrate in the upper layer of the grain mass. Topdressings are applied by adding the product to the last truckload of grain before it enters the auger or by raking the product into the top layer of the grain mass. Treatments can be applied to the stored grain at any time, but for best results, make application immediately after harvest before moth or beetle activity occurs.
Bacillus thuringiensis (Dipel, Biobit), Reldan, and Actellic are labeled as a topdress application. All of these products can suppress Indianmeal moth populations; however, existing populations in old grain may be difficult to control. Before making a surface application, remove any webbing that exists on the grain surface. If high numbers of Indianmeal moth worms (2 to 3 per square foot) exist, it is best to remove the webbing, fumigate, and then apply a surface application.
Apply wettable powder Bt products in a constantly agitated water suspension by mixing 1 pound of the formulation to 10 gallons of water. Use a sprinkler can or sprayer to apply 0.6 pint of the suspension per bushel as the last truckload is augered into the bin. Or apply 10 gallons of the suspension to 500 square feet of the grain surface in the bin and mix thoroughly with a scoop or rake to a depth of 4 inches. More thorough coverage may be achieved by dividing the recommended dosage into three applications and mixing the grain between applications. Apply Dipel dust as a topdressing at the rate of 4 pounds per 500 square feet and mix thoroughly to a depth of 2 to 4 inches. Remember that Bt product is only effective against certain caterpillars, such as the Indianmeal moth; it will not control weevils and secondary beetles.
As a topdressing, the rate of Reldan 4E per 1,000 square feet of grain surface is 3 ounces for wheat, 2.8 ounces for sorghum, 1.6 ounces for oats, and 2.4 ounces for barley. Mix the recommended rate of the concentrate with 2 gallons of water and apply to every 1,000 square feet of grain surface. Reldan 3% dust can also be used at the rate of 7 pounds per 1,000 square feet. Reldan is not labeled for corn.
For Actellic 5E, use 3 ounces in 2 gallons of water per 1,000 square feet for use only on corn and grain sorghum. It cannot be used on small grains except in situations where the small grain will be exported to other countries. Apply one-half of the mixture as a spray to the grain surface and rake the mixture into the grain to a depth of 4 inches. Apply the remaining one-half of the mixture to the raked surface.
Slow-release DDVP or dichlovos (Vapona) strips are registered for use in grain bins. Placement of these strips in the bin headspace will help to protect against infestations of Indianmeal moth; however, strips work best in an airtight bin. Use one strip per 1,000 cubic feet of headspace above the grain and replace every 3 to 4 months.
