Preventative Measures for Stored Grain Pests Back »

Granary weevil (Sitophilus granarius). This insect thrives in stored grain and is regarded as a stored grain pest. [CC BY 3.0], via Wikimedia Commons

Written collaboratively by Adam Varenhorst, Patrick Wagner, and Amanda Bachmann.


As harvest rapidly approaches, it is time to inspect grain storage facilities and conduct pre-harvest bin maintenance. These preventive measures can prevent insects and other pests from infesting the new crop of stored grain during the fall. Although the majority of scouting for insect pests occurs during the summer, it also must continue until the grain is marketed and delivered.

Federal Grain Inspection Service "Infested" Designation

While grain is being stored, it is susceptible to insect feeding which can cause both direct and indirect damage. Direct damage to the grain occurs when insects feed directly on the kernel or seed. This feeding results in reductions to germination, weight, and the nutritional value of the seeds. Indirect damage to the grain occurs when the presence of insects (alive or dead) causes heat damage, promotes mold growth, or contaminates the grain with dead insect parts. When these conditions are present, the grain quality is downgraded and a reduction in the crop’s market value occurs. The current Federal Grain Inspection Service (FGIS) regulations used to determine if grain is considered infested can be found in Table 1. Pre-binning activities and routine inspections of stored grain can assist with preventing economic loss attributed to stored grain pests. Like summer insect pest management, an integrated pest management (IPM) plan should be implemented to achieve optimal results.

Table 1. FGIS designation levels for infested grain.

Crop Insects per 2.2 pounds of grain to receive FGIS “infested” designation
Barley, Canola,
Corn, Oats, Sorghum, Soybean, Sunflowers
• 2 live weevils
• 1 live weevil + 5 other live stored grain pests
• 10 other live stored grain pests
Rye, Triticale, Wheat • 2 live weevils
• 1 live weevil + 1 other live stored grain pest
• 2 other live stored grain pests
 

Sanitation

Sanitation is the most important component of a stored grain IPM program, and is thought to account for nearly 80% of an effective plan. The purpose of sanitation is to remove any pests (insects or rodents) that may currently be present in a bin, and to remove any food sources for potential future pests. In addition to cleaning, it is important to inspect the bin for any leaks and ensure that the bin is weatherproof. This can all be achieved by the following steps:

  1. Inspect the roof for any leaks and repair if present.
  2. Inspect the bin for any cracks, holes, or gaps and seal if present.
  3. Remove old grain from bin. It’s never advised to store new grain on top of old grain.
  4. Remove any grain, dust, or debris from inside the bin by sweeping or vacuuming. Be sure to brush down the walls as well as the floor.
  5. Clean any grain spills around the outside of the bin. These spills can serve as a food source for pests before they infest a bin. They may also attract pests to the bin site.
  6. Clear a perimeter of 10 feet around the bin of any vegetation or debris.
  7. Clean grain handling equipment prior to harvest. This includes augers, wagons, grain carts, trucks, combines, grain cleaners, and aeration fans.
  8. Seal the bin door once the bin has been filled.

If proper sanitation is conducted prior to storing grain the risk of infestation is greatly reduced.

Pre-Binning Insecticide Treatment

Pre-binning insecticide treatment should occur after a proper sanitation has occurred. The walls and floors of the bin should be treated with a residual insecticide 2-3 weeks prior to harvest. These treatments are most effective when temperatures are over 60°F due to increased insect activity. The outside walls and base of the bin may also be treated with an insecticide labeled for perimeter use. Table 2 contains a few of the common residual insecticides that may be used for this treatment.

Table 2. Residual insecticides labeled for pre-binning applications of empty bins.

Insecticide
(active ingredient)

 
Re-entry interval (REI) Comments
Tempo SC Ultra
(beta-cyfluthrin)
When spray has dried Do not allow run-off to occur.
Suspend SC
(deltamethrin)
When spray has dried Do not allow run-off to occur.
Centynal
(deltamethrin)
When spray has dried Do not reapply within 21 days.
Malathion 5EC
(malathion)
12 hours Use malathion products according to their label.
Pyronyl
(pyrethrin)
12 hours Do not reapply within 30 days.
Dryacide and Insecto
(silicon dioxide)
Once dust settles Over application of product may reduce grade of grain.

*Always follow label instructions and wear proper personal protective equipment.
**This list is not meant to be comprehensive.

 

Stored Grain

Stored grain should be cleaned prior to storage for the removal of cracked grain, dust, or any other debris that can cause aeration issues later in the storage process. To ensure optimal airflow, grain should be leveled once the bin is full. Areas where the grain is peaked can provide optimal conditions for stored grain insect pest outbreaks. Stored grain should also be uniformly aerated because uneven drying and cooling can result in “hot spots”, which favor insect activity and mold growth. Grain should be dried prior to storage and then cooled to a point below 55°F as soon as possible to reduce insect development and activity. The cold temperatures will also inhibit mold growth.

Stored grain typically does not require a protectant insecticide application, but it should be considered if the grain is going to be stored for more than one year. Protectant insecticides should be applied after the grain has been dried, and the moisture level is uniform. Depending on the insecticide label it may be applied at the auger while the grain is being filled. A protectant insecticide may also be applied as a top-dressing once the bin is filled. Table 3 provides a list of some common protectant insecticides.

Stored grain should be inspected on a weekly basis while the temperature of the grain is above 55-60°F. Once the grain temperature falls below 55°F it should be inspected every two weeks. When inspecting, the grain samples should be taken from several locations and from several depths at each location. It is important to pay attention to the condition of the surface of the grain, and also of any potential “hot-spots”. Always use safety precautions when sampling grain, and ensure that crusts haven’t formed on the grain surface.

Table 3. Common stored grain protectant insecticides.

Insecticide
(active ingredient)
Re-entry Interval
(REI)
Comments
Dipel DF
(Bacillus thuringiensis kurstaki)
4 hours To be applied as a top-dressing to the top 4 inches of stored grain. Not effective against beetles. Labeled for all crops.
Biobit HP
(Bacillus thuringiensis kurstaki)
4 hours To be applied as a top-dressing to the top 4 inches of stored grain. Not effective against beetles. Labeled for all crops.
Centynal
(deltamethrin)
When spray has dried May be applied while grain is being loaded into the bin. Do not reapply within 21 days. Labeled for barley, corn, oats, rice, rye, sorghum, and wheat.
Nuvan Prostrips
(dichlorvos)
N/A Treatment normally lasts 4 months. Place strips in the headspace of the bin. Wear protective gloves when applying strips. Labeled for all crops.
Actellic 5E
(pirimiphos-methyl)
When spray has dried. May be applied while grain is being loaded into the bin, or as a top-dressing. Cannot be used for both. Do not make more than one application per year. Labeled for shelled corn and sorghum.
Pyronyl
(pyrethrin)
12 hours Do not reapply within 30 days. May be applied while the grain is being loaded into the bin. Labeled for barley, beans, corn, flax, oats, rye, sorghum, and wheat.
6% Malathion grain dust
(malathion)
12 hours Apply to grain prior to loading the bin. Do not reapply to grain within 7 days of selling. Labeled for barley, corn, oats, rice, rye, and wheat.
Diacon IGR and Diacon-D IGR
(S-methoprene)
30 minutes May be applied while grain is being loaded into the bin, or as a top-dressing. Labeled for all crops.
Dryacide and Insecto
(silicon dioxide)
Once dust settles May be applied while grain is being loaded into the bin. Over application of product may reduce grade of grain. Labeled for all crops.
*Always follow label instructions and wear proper personal protective equipment.
**This list is not meant to be comprehensive.
 

Stored Grain Insects

Stored grain insects include any insects that are present in the stored grain. Proper identification of these insect pests is important because some are internal feeders and others are external feeders. Internal feeders cause damage to the grain by feeding on the kernel, while external feeders feed on grain dusts, cracked kernels, or other grain debris. Some of the most destructive stored grain pests include the granary weevil (aka wheat weevil), maize weevil, and rice weevil. Purdue University Extension constructed a key for the stored grain beetles that may be found in a bin. In addition to beetles, Indian meal moth larvae can also cause damage to stored grain.

Treating an Infestation

When an infestation of internal feeding stored grain pests is detected, there are four management options available. The first is to move the grain and apply a protectant as it is being reloaded. The second option is to feed the grain as is to prevent spoilage. The third option is to sell the grain at a discounted price. The fourth and final option is to fumigate the bin. Fumigant insecticides are extremely dangerous, and are very hazardous to applicators due to their application method. Because of this, it is recommended to have a licensed professional apply fumigant treatments.


References:

  • Hodgson, E. and K. Holscher, 2009. Think about stored grain pests before harvest. ISU Integrated Crop Management News. Iowa State University Extension, Ames, IA.
  • Mason, L. J. and J. Obermeyer, Rev. 2010. Stored grain insect pest management. E-66-W. Purdue University Extension, West Lafayette, IN.
  • Peairs, F.B. Rev. 2010. Insect damage to farm-stored grain. Factsheet No. 5.545. Colorado State University Extension, Fort Collins, CO.
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