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Posted ?? October 2018. PMN Crop News.

How Do I Manage Insects in My Stored Grain?

Source: South Dakota State University iGrow Article.

By Adam J. Varenhorst, Assistant Professor & SDSU Extension Field Crop Entomologist, Amanda Bachmann, SDSU Extension Pesticide Education & Urban Entomology Field Specialist, Philip Rozeboom, and Patrick Wagner, SDSU Extension Entomology Field Specialist


Brookings, South Dakota (September 24, 2018)--Throughout the year, it is possible to find an infestation of insects in stored grain. The general rule of thumb is the longer grain is stored, the greater the chance of an infestation occurring. As mentioned in a previous article, there are many important steps to be taken to reduce the likelihood of infestation. Under most storage circumstances it is not necessary to treat grain with a protectant insecticide prior to binning (See Table 2 for information on protectant insecticides). This is true for grain that will be removed from storage by May or June of the following spring, or that will be used on-site as livestock feed within one year of harvest. A protectant insecticide should be applied to grain that is expected to be stored for more than one year. If a protectant insecticide application is necessary, it should only occur after the grain has reached the optimal storage moisture. These insecticides can be applied at the auger while the bin is being filled, or as a surface treatment that is referred to as either top-dressing or capping-off.

Stored grain with a temperature above 55-60°F should be inspected each week, and every two weeks when the temperature is below 55°F. When inspecting stored grain, it is important to remember the potential hazards of grain that is in storage. If an insect infestation is detected in stored grain the grain can either be moved and have a protectant insecticide applied, fed to livestock as-is, be sold at a reduced market value, or be fumigated (Table 1). Due to the hazardous nature of fumigant insecticides we strongly recommend that the application of these is done by a hired professional. Many of these products are activated by moisture, including the moisture present in air. That means the second the seal is removed or the package is opened the product is active. The application of fumigants should be done with a forced air or oxygen provided respirator system to prevent any negative health impacts including death. Always read and follow the label directions when using any pesticide product.

The Seven Components to a Stored Grain Integrated Pest Management (IPM) Plan

Step 1: Structural and Maintenance Components: keep bins clean and repaired.

All season:

• Keep a 10 ft. perimeter around the bin free of vegetation and trash.

• Clean up grain spills outside of the bin.


• Bins built on moisture-proof base

• Confirm that bin facilities are weather tight and rodent proof.

• Screen ventilation openings to prevent entry of rodents and birds.

• *Do not mix new and old grain; remove all old grain from bin or fumigate old grain.

• *Clean the bin wall, ceiling, ledges, floors, and sills prior to filling with new grain.

• *Clean combine, wagons, grain carts, trailers, and prior to handling new grain.

• Dispose of any debris removed from bins or machinery as insects may infest it.

• Examine area to determine if rodent bait stations are necessary.


• Seal any holes, and caulk around any doors.

• Do not seal roof aeration exhaust of inlet vents except during fumigation.

Step 2: Residual insecticide sprays (Table 2).


• Spray the wall surfaces, ledges, floors, and sills with a residual insecticide.

• Spray outside walls and outside base.

• For long-term storage (> 1 year) consider fumigating the area beneath the slotted floor. (Table 2 for information regarding insecticides)

Step 3: Condition grain: store clean, dry grain.


• For long term storage corn moisture should be 15% or less.

• Use a grain cleaner to remove cracked kernels and other debris.

Step 4: Proper aeration.


• Run bin fan and stirator to ensure uniform temperatures and prevent moisture buildups. This will reduce mold growth.

Step 5: Use insecticide protectants (Table 2).

• Treat grain as it is moved into storage.

Step 6: Regularly inspect grain.


• Monitor the grain regularly. For grain above 55-60°F inspect weekly. For grain below 55°F inspect every two weeks.

• Use a grain probe to take samples in a pattern from the surface, and also from the base of the grain mass.

• Take samples from the center to the areas near the wall, with samples being no further than 20 feet apart.

• “Hot spots” felt on the grain surface or unusual odors are indicators of insect activity, and should be examined.

• During the winter insects will move to the center of the bin, so sampling at that location is important.

Step 7: Treating detected infestations when necessary.


If an insect infestation is detected:

1. Move the grain and retreat as in Step 5. It is possible to kill some of the insects if the grain is moved during cold weather.

2. Feed the grain to livestock.

3. Sell at a reduced price

4. Fumigate (Table 1)

*These precautionary maintenance steps should be taken two weeks prior to binning.

Bin Sampling Safety Protocol

There are many potential hazards associated with sampling inside of a grain bin. For instance, suffocation can occur in grain bins due to bridged grain. Bridged grain is occurs when grain mats together and forms a false floor. When the false floor is broken during sampling procedures cave-ins can occur. Where possible:

1. Always have another person with a cell-phone outside the bin in case there is a problem.

2. Wear a harness that is attached to a properly secured rope when entering a grain bin.

3. Use a pole to break up crusted grain from a distance.

4. If the grain begins to flow stay near the outer wall of the bin and continue walking and get to the bin ladder as quickly as possible.





Bin Aeration

Stored grain insect pest development begins to slow when grain temperatures drop to around 60°F, and essentially stop when the temperature drops below 55°F. Because of this it is important to lower grain temperatures and reduce the risks of stored grain pests. Stored grain can be cooled once the outdoor temperatures begin to drop in the fall. For bins that are equipped with fans, run the fan during these cooler temperature periods to cool the grain. In addition to reducing potential insect issues, proper aeration of the grain will help maintain uniform temperatures throughout the bin. This will eliminate “hot pockets” that are favored by insects and mold. To ensure optimal airflow level off the grain once the bin has been filled. When the grain is not level, areas with peaks can provide optimal conditions for stored grain insect outbreaks.

Common Stored Grain Insect Pests of Corn

There are several species of insects that feed on stored grain. Both the immature (larval) and adult stages of stored grain beetles are capable of causing damage to grain, while only the larval stage of the stored grain moths cause damage. These insect pests can be grouped based on whether they are internal feeders or external feeders. Internal feeders feed within the kernels while external feeders will consume grain dusts, cracked kernels, and other grain debris. Below are the common internal and external stored grain pests. In addition to these, other species including the foreign grain beetle and hairy fungus beetle may be observed in a bin. These beetles are feeding on the molds or fungi growing on the grain.

Internal Feeders

Of the internal feeders, the weevils (Figure 1, Figure 2, and Figure 3) are generally given the most attention because they are among the most destructive pests of stored grain. The larvae of grain weevils develop within the kernels, and when infested grain is left undisturbed for long periods of time can cause nearly complete destruction. Adult weevils are easily distinguished from other beetles by their elongated snouts.


Figure 1. Granary weevil (aka wheat weevil). (Courtesy: Pest and Diseases Image Library,



Figure 2. Maize weevil. (Courtesy: Gary Alpert, Harvard University,



Figure 3. Rice weevil. (Courtesy: Pest and Diseases Image Library,


The lesser grain borer (Figure 4) is a pest of a wide variety of grains. The larvae and adult of this pest are damaging. The larvae of this pest are unable to infest undamaged kernels. In addition to kernels, the larvae are also able to develop on grain meal.


Figure 4. Lesser grain borer. (Courtesy: Pest and Diseases Image Library,


The larvae of the angoumois grain moth (Figure 5, adult moth) are typically not a pest of shelled grain. However, the larvae are a pest of ear corn and can infest the corn before it is harvested. The larvae feed inside kernels, and cause an unpleasant smell. During warm falls, several generations of the moth can be completed resulting in significant damage.


Figure 5. Angoumois grain moth adult. (Courtesy: Clemson University-USDA Cooperative Extension Slide Series,


External Feeders

The stored grain pests that are external feeders are present in the grain because grain dusts, cracked kernels, or other grain debris was present and is a viable food source. Similarly, to internal feeders, the best management for these insects is prevention. The presence of fungus feeders indicates that the grain is moldy. Proper aeration and grain cleaning can prevent most infestations caused by external feeders.

The cadelle beetle (Figure 6), confused flour beetle (Figure 7), flat grain beetle (Figure 8), red flour beetle (Figure 9), and sawtoothed grain beetle (Figure 10) are present in the grain due to the availability of cracked kernels, dust, and other grain debris. In some instances, these beetles will feed on kernels that were damaged by internal feeders.


Figure 6. Cadelle beetle. (Courtesy: Clemson University-USDA Cooperative Extension Slide Series,



Figure 7. Confused flour beetle. (Courtesy: Pest and Diseases Image Library,



Figure 8. Flat grain beetle. (Courtesy: Gary Alpert, Harvard University,



Figure 9. Red flour beetle. (Courtesy: Pest and Diseases Image Library,



Figure 10. Sawtoothed grain beetle. (Courtesy: Pest and Diseases Image Library,


The larvae of the Indian meal moth (Figure 11, adult moth) cause direct damage to the grain by feeding on the seed germ. The larvae of this pest also reduce the quality of grain by producing waste and constructing silken webs in the grain. These webs are often observed on the top surface of the grain and can become quite thick.


Figure 11. Indian meal moth adult. (Courtesy: Pest and Disease Image Library,


Adam J. Varenhorst

Amanda Bachmann

Patrick Wagner