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Managing stored grain to minimize risk of storage losses

Phillip Glogoza and David Nicolai
Regional Extension Educators-Crops, Moorhead and Hutchinson, MN

Grain harvest is in full swing across the state. It is not too late to review basic on-farm grain storage principles for maintaining quality of stored commodities. Harvest should include preparation of storage structures to receive grain. Preparation includes several practices that aide in preventing pest infestations from developing within our storage structures.

Multiple practices should be implemented on farm to maximize grain quality. These include using appropriate production and harvest practices, maintenance and proper use of grain handling equipment, drying systems and storage structures. There are four simple steps to maintain post-harvest quality sanitation, loading, aeration, and monitoring to protect stored grains from insects, weather, rodents, self-heating, molds, mycotoxins, and pesticide residues.


Be sure that the storage structure as well as any grain handling equipment (conveyors, wagons, trucks, elevators) are free of leftover grain. Cleanup is most effective when completed in early spring or immediately after bins are emptied. Unnecessary grain residue present during early summer only allows insect infestations to increase during warming temperatures. Even small amounts of moldy or insect-infested grain left in equipment can contaminate a bin of new grain. Repairs such as sealing cracks and/or holes can be completed simultaneously. Old grain being moved to different storage should be screened and, if infested, treated by fumigating.

Always keep areas clean outside around the bin, beneath perforated floors and inside ducts in addition to cleaning the bin. Debris and grain spills outside the bin encourage rodents and insects which can then move in through openings. Keep weeds from growing around bin areas as these sites are ideal for pests to hide. On the inside, sweep or vacuum grain dust and old grain from floors, walls and ceilings where hiding places exist for stored grain insects. A common rule-of-thumb is, "If you can tell what has previously been in the bin, it is not clean".

In bins where the perforated floor cannot be easily removed, chloropicrin fumigant can be applied to control insects in the sub-floor area. Though still approved for use in empty bins, chloropicrin is NOT approved for direct application to grain. Chloropicrin is a highly toxic chemical, and as such, all label instructions and safety measures must be carefully adhered to. To use this product, an applicator must be a certified fumigator.

Roof leaks commonly lead to columns of spoiled grain. Check for these leaks by looking for light coming into the bin. Moisture coming into the bin through the seal between the bin and concrete will cause spoilage around the perimeter of the bin at the base. Check the seal since sealants do deteriorate. Water will run away from the seal at the base of the bin wall if the concrete is sloped away from the bin. Also check the seals around the doors and hatches.

After cleaning and repairing, use a residual bin spray to treat the insect surfaces of the bins at least two weeks prior to filling (see Table 1). It is better to treat during the warmer months when insects are active. If treatments were applied more than three months earlier, an additional treatment should be applied two to three weeks before new grain is placed in the bin.

Combining and loading into storage

Grain harvested with a clean and properly adjusted combine should also be run through a grain cleaner to further remove fine materials on which insects can feed. Grain with many broken kernels can also be run through a cleaner, but this will lead to additional weight loss. Clean, whole grain helps in insect management, but also is important in proper aeration of the grain mass during drying and storage. If fine materials are not present, air drawn into the grain from outside the bin will move more uniformly through the mass. A grain distributor is extremely helpful in preventing aggregations of fine material by spreading it uniformly across the grain mass. When a distributor is not used, the fine material will concentrate in a column at the center of the grain mass. Because this column is more dense, air will move around it through the less dense grain mass, allowing moisture to build up in the center of the bin. Moisture buildup is the first step in grain quality deterioration.

Loading refers to creating a grain mass with several basic properties that make it easy to handle and that lead to long life. The grain mass should be clean and dry, uniform without foreign material, and stored in an aerated weatherproof structure. Further, plan to protect against stored grain insects by using a grain protectant (see Table 1) if grain is to be held in storage for a year or more.

Specific practices that help approach the ideal grain mass include limiting kernel damage through slow drying methods, limiting the number of times grain must be handled, operating augers and elevators at capacity and slowest possible speeds, and storing grain in aerated structures.

If insecticide protectants are going to be applied to the grain, treat the grain stream just before it reaches final storage. Grain that is treated and then transferred long distances through numerous grain handling systems (such as pneumatic systems, belt augers, conveyors, spouts, legs, etc.) before storage will have less insecticide residue when the grain is finally loaded into the bin. It is very important to note that in situations where grain drying is necessary, an insecticide protectant should be applied after the grain has gone through the drier and has cooled. Commercial grain driers generate enough heat to rapidly degrade insecticides applied to grain prior to the drying process.

Immediately after the bin is filled and the grain leveled, apply a surface treatment ("top dressing") of an approved grain protectant. The surface treatment will help control insects that enter the grain through roof openings. Surface treatments alone generally will not keep the grain insect-free, but they can reduce insect populations during the storage period. Surface treatments are effective if the following limitations are understood. Surface treatment will not control an established insect infestation already in stored grain. The surface treatment should not be disturbed, since it provides the protective barrier against insect infestations.


In the fall, aerate to cool the stored grain and create a better storage environment in any bin larger than 2,000 to 3,000 bushel capacity. We should be able to cool grain to temperatures below 50 F by gradually cooling the grain through the fall. Insect activity is reduced at this temperature. Local winter temperatures allow us to achieve a target temperature for stored grain of 25 F for the winter. At this temperature, insect activity ceases and some mortality will occur for a number of our stored insect pests. Keep grain temperature less than 50°F at all times of the year. In the upper Midwest, aerate to cool grain to 20° to 30°F for winter storage.

The grain mass should be cooled and dried uniformly. Move cooling front completely through and out of the grain mass and maintain low grain temperatures as long as possible during storage. It is not necessary to rewarm dry grain with fans during the spring and summer. The recommended moisture levels for various grains for short term storage and long term storage are summarized in Table 2.


Check stored grain regularly for temperature, moisture, insects and molds. Inspect stored grain every 7 to 14 days when either outdoor or grain temperatures are greater than about 50F, but if the grain is in good condition and has been cooled to less than 30F, you can increase the inspection interval to once every three to four weeks during cold weather. Check for insects by screening them from the grain, examining kernels for damage, looking for webbing, detecting off-odors, or monitoring grain temperatures. Insect infestations can raise grain temperatures to as high as 110°F. During the summer and fall, insect infestations are usually near the surface of the grain. During cold weather stored grain insects will congregate at the center and lower portions of the grain mass and may escape detection until extensive heating has developed.

Table 1. Insecticides registered for use to protect stored grains from insects. Updated September, 2006

SiteInsecticideMaterials to Use
Residual Bin Sprays: Clean, sweep and spray all bins before harvest. Note: Do not add grain to a treated bin for at least 24 hours or until walls have dried thoroughly.
All BinsDiacon II (methoprene)Active ingredient is an insect growth regulator. It prevents the development of larvae into adults. Adult insects are not controlled.
diatomaceous earthDistribute dust to provide an even coating on interior surfaces. Check the label for suggestions on treating methods.
Malathion 5 ECMay not provide control of Indian meal moth. Read the label for recommendations for use.
Tempo SCCheck product label for rates of application. Do not apply directly to grain.
Storcide IIStorcide II combines the active ingredients of Reldan (chlorpyrifos methyl) and Decis (deltamethrin)
Surface Treatment: Apply insecticide to surface after grain is binned. Note: To ensure maximum control, remove all surface crusting and webbing prior to treatment.






Dipel (Bacillus thuringienesis)Use for Indian meal moth larvae only. As a surface treatment, apply 4 lb/500 sq. ft. of grain surface area: mix into top 4 inches
diatomaceous earth2.0 lbs. per ton. Treat only the top 1 ft. of the grain mass
Grain Protectant: All the grain is treated when bin is being filled. Insecticides may be applied as a spray of dust to the grain as it is being augered into the bin. These products may also be used for treatment of hte grain surface for registered commodities.
Corn SorghumAcetellic 5ENo food or feeding restrictions. Lesser grain borer is not listed as a target pest.



Diacon II (methoprene)Active ingredient is an insect growth regulator. It prevents the development of larvae into adults. Adult insects are not controlled.
Malathion 6% DustMay not provide control of Indian meal moth. Malathion products not labeled specifically for application to stored grain should not be used.
Reldan*Do not apply to corn. Product sales were ended December 31, 2005. End-users with product in their possession may continue use according to label directions.
Storcide IIStorcide II combines the active ingredients of Reldan (chlorpyrifos methyl) and Decis (deltamethrin). Storcide II does not have export restrictions on the label.
*Note: Due to the potential for residues of Reldan in malt from treated barley, the American Malting Barley Association disapproves of the use of this insecticide on malting barley.

Table 2. The Recommended Storage Moisture levels for grain (percent wet basis for clean, aerated grain crops).

Storage Time
Up to 6 Months
More than 6 Months
Edible beans
Small grains
Sunflower (oil)

Stored Grain Management Resources:

Post-Harvest Handling of Crops

Program Leader: Bill Wilcke
University of Minnesota, Bioproducts and Biosystems Engineering

Grain Storage Tips:

Factors and Formulas for Crop Drying, Storage and Handling
William Wilcke and Gary Wyatt (pdf)

Post Harvest Grain Quality & Stored Product Protection Program

Purdue University

Grain Drying, Handling, & Storage

Project Leader: Dr. Kenneth J. Hellevang, P.E.
North Dakota State University Extension Service
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