Steps to Prevent Stored Grain Infestations

 

As wheat harvest is underway it is important to ensure that grain bins are prepared in the best possible manner to prevent insect infestations. The general rule of thumb is the longer grain is stored, the greater the chance of an infestation occurring. There are seven steps that can be taken to help reduce the chances of having infested grain. 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. However, 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 associated hazards. For instance, suffocation can occur in grain bins due to bridged grain; bridged grain 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:

 

 

The seven components to a stored grain integrated pest management (IPM) plan are as follows:

 

 

 

 

 

 

 

 

 

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. This 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. Applicators using fumigants must also prepare and follow a fumigant management plan.

 

 

 

 

 

 

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.

 

 

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.

 

 

 

Of the internal feeders, 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.

 

 

 

 

 

 

 

 

 

 

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, Bugwood.org

 

 

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.

 

 

 

 

The stored grain pests that are external feeders are present in the grain because grain dusts, cracked kernels, or other grain debris are present and are a viable food source. Similar 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.

 

 

 

 

 

 

 

 

 

 

 

 

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.