Prevention of Stored Grain Pests

With harvest just around the corner it is time to start thinking about pre-harvest bin maintenance and ultimately preventing the new crop of stored grain from being infested by insects. Unfortunately, scouting and management decisions don’t stop once the crop is harvested, and actually continue until it is sold and delivered.

During storage the grain is susceptible to both direct and indirect damage that can be caused by insect feeding. Insect pests of stored grain are capable of causing direct damage to the grain by feeding on the kernel, which results in reduced germination, weight, and nutritional value. They can also cause indirect damage by causing heat damage, promoting mold growth, or contaminating the grain with dead insect bodies or parts. These conditions ultimately result in a downgrading of the grain quality and a reduction of the crop’s market value. To prevent economic loss attributed to stored grain pests, implement an integrated pest management (IPM) plan.

Sanitation
This is considered the most important part of a stored grain IPM plan, and is believed to account for as much as 80% of an effective plan. The goal of sanitation is to remove any food sources for potential pests, and also any pests that are currently infesting the bin. In addition, a goal of sanitation is to ensure that the bin is weatherproof.

For proper sanitation:

If proper sanitation is conducted prior to storing grain it is possible to prevent infestations and the insecticide treatments associated with them.

Pre-binning Insecticide Treatment
Prior to filling the bin, but after proper sanitation, the walls and floors should be treated with a residual insecticide. The outside walls and outside base of the bin may also be treated with an insecticide. This treatment should occur 2-3 weeks prior to filling the bin, and is most effective when temperatures are over 60°F due to increased insect activity. Table 2 contains some common residual insecticides that may be used for this treatment.

Storing Grain
Grain that is going to be stored should be cleaned to remove cracked kernels, dust, or any other debris that can cause aeration issues later in the storage process. To ensure optimal airflow grain should also be leveled once the bin is full. Areas with peaks can provide optimal conditions for stored grain insect outbreaks. Uniform aeration is crucial as uneven drying and cooling can result in “hot spots”, which can also 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.

Generally stored grain does not require a protectant insecticide treatment unless it 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 it may be applied at the auger while the bin is being filled or as a top-dressing once the bin is filled. Table 3 provides a list of some common protectant insecticides.

Stored Grain Insects
If insects are present in the stored grain, proper identification is important, as some are internal feeders while 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, the larvae of the Indian meal moth 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. Move the grain and apply a protectant as it is being reloaded, feed the grain as is, sell the grain at a discounted price, and the fourth option is to fumigate the bin. Fumigant insecticides are extremely dangerous and due to their application method very hazardous to the applicator. Because of this, it is recommended to have a licensed professional apply fumigant treatments.

Source: Adam J. Varenhorst and Billy Fuller, South Dakota State University 

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