Preparing to store wheat

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

As wheat harvest approaches in Michigan, now is the time to think about storage. Wheat is put into storage under the assumption that its condition will not deteriorate. Insects are one factor that can reduce grain quality and grade during storage by directly feeding on kernels and by reducing test weight. As insects feed, fine matter accumulates in the bin and reduces airflow. This fine dust consists of tiny pieces of wheat, dead insect bits, and caterpillar webbing. Insect feeding also produces hot spots in the grain. Reduced airflow and hot spots, combined with moisture, often lead to another problem; growth of fungi, some of which produce toxins.

Prevention and sanitation

The best way to manage an insect infestation in a bin is to avoid one in the first place. Spilled grain, contaminated equipment and dirty bins provide food for insects. These insects move into newly-stored grain to start new infestations. Cleaning up old grain is key to keeping new grain clean. Good sanitation pays off in the long run, reducing or eliminating the need for insecticide applications. This is important because USDA food testing programs find that a high percentage of wheat samples have pesticide residue. Sanitation and prevention should be part of your routine prior to storing wheat at your facility or farmstead.

  • Clean grain handling equipment (augers, combines, wagons, scoops, trucks). Kernels and fine material stuck in equipment provide a breeding ground for insects.
  • Clean inside the bin and if possible, beneath the floor. Having removed a few floors, I know it’s an unpleasant task. However, under the floor plates can be several inches of fine grain dust, rodent droppings, insect parts, and fungal spores. If an annual cleaning is impractical, make a schedule and try to clean a bin every few years.
  • Clean around the bin. Clean up grain spills and remove weeds from a ten-foot border around the bin. Spilled grain and tall vegetation provides food and shelter for both insects and rodents.
  • Seal all cracks and crevices, entry points for insects. Cover or screen fans when not in use. Keep doors closed, and make sure they seal when shut.

Sanitation may be enough to avoid an insect infestation in Michigan bins. Much of our wheat will be stored only for a short time, heading to local mills or to the East Coast by fall. If wheat is stored for a longer period, we have the advantage of fall and winter temperatures to keep the grain mass cool, reducing insect activity. With an excellent sanitation program, well-maintained bins, and a short storage period, insecticides on wheat can be avoided altogether.

Bin sprays

If your farm has a history of insect problems in grain, or if it is difficult to clean bins and equipment, an insecticide may be useful. Bin treatments are used in and around empty structures after cleaning, but before adding grain. They kill insects still in the area and create a barrier to infestation. Treat bin floors and walls up to six feet, the foundation, and ground directly around the bin, as well as equipment. Concentrate on cracks, crevices, and other hard-to-clean areas that harbor grain dust and insects. The following is a list of products registered as bin treatments. Read the product label carefully before using any of these insecticides, as formulations can vary and labels may change from year to year. Some products are registered only for bins containing certain grains.

  • Tempo (cyfluthrin - a pyrethroid). Registered for all indoor warehouses, bins, grain-handling equipment, trucks, rail cars and areas around bins. Tempo is not registered for direct application to grain itself.
  • Storcide II (chlorpyrifos-methyl + deltamethrin): This product replaced Storcide and Reldan.
  • Malathion - numerous formulations (an older OP). Registered for use in structures that will contain barley, corn, oats, rye and sorghum. Do not use in bins that will contain soybeans. Refer to individual product labels, as some may not be registered for use on stored grain and others are being phased out.
  • Diatomaceous earth. Many products are available, such as Insecto, Protect-It, and PermaGuard. DE is a chemically inert dust that abrades the insect cuticle, or outer skeleton, causing the insect to lose water, dry out and die.

If you follow these recommendations, you will likely not need to use an insecticide on the grain itself or during storage in Michigan. Compared to southern states, we can cool grain faster after harvest, reducing insect and fungal activity.

Treatments directly to grain

If you anticipate storing the wheat for a long period, you may decide to apply insecticide to the grain itself. There are two different types of insecticide applications on wheat. If the bin and the wheat entering the bin is clean, and it is not layered over old grain, a “top dress” or surface treatment may be all that is needed. A surface or barrier treatment is applied on the last grain going into the bin or directly on the grain surface once the grain is in the bin. A surface treatment must not be disturbed after application, since this ruins the barrier. Surface treatments protect against insects entering from the top of the bin; for example, Indianmeal moth, but will not control insects already present lower down in the grain mass (for example, if you put new grain over infested old grain).

Protectants are insecticides directly applied to the grain stream as it enters the bin. These treatments are designed to control infestations throughout the entire bin. In Michigan, protectants are generally not necessary if grain will be used or sold within six months, and if the bin is properly cleaned, sealed, and sprayed with a sanitary spray (see above) prior to fill.

Products labeled as protectants and/or surface treatments for wheat include:

Storcide II (chlorpyrifos methyl + deltamethrin). For use on barley, oats, and wheat.

  • Malathion. Again, many trade names and formulations, registered for different sites and uses. Refer to individual product labels, as some may not be registered for use on stored grain, and others are being phased out. Be aware that grain that has been treated with malathion may not be acceptable to some millers.
  • Diatomaceous earth. Registered for barley, corn, oats, rye, soybean, sorghum, sunflower, wheat. Note that different formulations are registered for different crops, therefore check the labels. Diatomaceous earth is abrasive and may cause equipment wear. Newer formulations of Diatomaceous earth require a lower application rate, and may be easier to use than older formulations.
  • Pyrethrins. Sold under several trade names. Registered as a surface treatment for barley, corn, oats, sorghum, sunflower, and wheat. It is not registered for soybean.
  • Diacon (methoprene). Registered as a surface treatment for barley, corn, oats, sorghum, and wheat, it is not registered for soybean. Methoprene is an insect growth regulator which disrupts insect development. It thus controls larvae, but not adult insects.
  • Dipel, Top-Side, etc. (Bt). Registered as a surface treatment for barley, corn, oats, rye, sorghum, soybeans, sunflowers and wheat. Bt kills Indianmeal moth larvae. Some formulations are acceptable on organic wheat. Bt will not control adult moths, weevils and grain beetles.

Additional insecticide notes: Actellic (pirimiphos-methyl), which can be used as a protectant on corn, is not labeled for wheat. Sales of Reldan, which was available as a bin spray and protectant, ended December 2005. Existing stocks should be gone. Grain treated with Reldan has until 2009-10 to move through channels of trade.

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