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Corn+Soybean Digest

Prevent Insect Infestation in Grain Bins

If the weather continues to stay warm this fall, it may be another busy season for insects as they infest grain bins.

"Take some time now to prepare your storage bins and prevent potential stored insect problems through good bin management," says Janet Knodel, North Dakota State University Extension service entomologist. "There are some good reasons to prevent insect problems in the bin. Most countries have a zero-tolerance policy for insects in grain destined for export. Also, practices to prevent insect grain bin infestation are relatively simple and cost a lot less than practices commonly used to protect a growing crop from insect losses."

Several insect species infest stored grains in North Dakota, including confused flour beetle, Indian meal moth, rice weevil, lesser grain borer and red flour beetle. Damage caused by these insects includes reduced grain weight and nutritional value, contamination, odor, mold and heat damage, which lowers the grain quality.

The first step is to make sure that the bins are clean and free of insect-infested grain. Leftover grain should be removed from the bin and the walls should be swept and vacuumed. All grain-handling equipment, including augers, combines, trucks and wagons, should be cleaned thoroughly and grain residues removed before harvest.

A residual bin spray, such as Malathion, Tempo or Storcide II, should be applied to all interior bin surface areas two to three weeks before new grain is placed in the bin. The treatment will kill insects emerging from their hiding places (cracks, crevices, under floors and in aeration systems). Also, insects crawling or flying in from the outside will be killed.

"When cleaning the bins, remember to get under aeration floors and inside aeration tubes," Knodel says. "These are great spots for insects to hang out while waiting for you to fill the bin."

Remove any vegetation or weeds that may attract and harbor insect pests within 10 ft. of a bin and preferably the whole storage area. Follow by spraying the cleaned area around the bin with a residual herbicide to remove all undesirable weedy plants.

Repair and seal all damaged areas to the storage structure. This will help prevent insect infestation and reduce water leakage, which leads to mold growth.

Whenever fans are not operated, they should be covered and sealed to reduce the opportunity for insects and vertebrates to enter the bin through the aeration system.

If newly harvested grain and/or insect-free grain must be added to grain already in storage, the latter should be fumigated to prevent insect infestation. If grain will be in storage for one or more years, it is recommended that grain be treated with an approved insecticide as it is augured into the bin. Grain protectants kill insects as they crawl about or feed on treated grain or grain fragments.

"Do not apply grain protectants before high-temperature drying because extreme heat will result in rapid volatilization and reduced residual qualities of the pesticides," Knodel says. "Grain protectants applied to 13% moisture grain will have a greater residual life than grain at 15% or more moisture. Moist grain also is more attractive to insect infestations."

Canadian research shows that pea flour extract has some natural repellent properties and insecticidal activity against stored grain insects. Patents have been obtained for the U.S. and Canadian extract process. Agriculture and Agri-Food Canada is looking for a partner to commercialize the pea flour extract.

"Another important step in preventing insect infestations is immediate cooling of the grain after harvest," Knodel says. "Grain insects that are flying in the general area will be attracted to harvested grain by smell. They can find and infest grain on the truck or through an open grain-bin hatch."

If the grain is warm (above 50°), insects will start feeding and reproducing immediately. When grain temperatures are above 50°, bins should be inspected for insect activity every two weeks. Stored grain insect pests generally are inactive at temperatures below 50°.

Use a grain probe to determine what species of insect pests are infesting the grain and the extent of infestation within the grain mass.

Consult the "2007 Field Crop Insect Management Guide" at for a complete list of stored grain insecticides.

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