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Preventative Measures For Stored Grain Pests

Sep 20, 2016
By Adam J. Varenhorst
Assistant Professor & SDSU Extension Field Crop Entomologist
 
Granary weevil (Sitophilus granarius). This insect thrives in stored grain and is regarded as a stored grain pest. 
 
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.
CropInsects 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.
  9. 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 driedDo not allow run-off to occur.
Suspend SC
(deltamethrin)
When spray has driedDo not allow run-off to occur.
Centynal
(deltamethrin)
When spray has driedDo not reapply within 21 days.
Malathion 5EC
(malathion)
12 hoursUse malathion products according to their label.
Pyronyl
(pyrethrin)
12 hoursDo not reapply within 30 days.
Dryacide and Insecto
(silicon dioxide)
Once dust settlesOver 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 hoursTo 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 hoursTo 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 driedMay 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/ATreatment 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 hoursDo 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 hoursApply 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 minutesMay 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 settlesMay 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.
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