Now is the time to start thinking about taking measures to protect the grain you will put in bins this fall from stored grain insects.

Stored grain insect pests are an economic concern in Iowa—they reduce the quality of grain in bins on too many farms each year. Infestations can directly reduce grain weight and nutritional value of the grain, in addition to indirectly causing mold and other contamination.

There are two types of stored grain pests. Primary stored grain insects feed within the intact kernels while secondary pests feed on broken kernels or grain dust. Examples of primary pests include rice weevil, granary weevil and maize weevil. Common secondary pests are red and confused flour beetles, and the sawtoothed grain beetle and Indianmeal moth. You should use integrated pest management strategies of stored grain insects to prevent infestations and thus protect your investment. That's the advice of Erin Hodgson and Ken Holscher, Extension entomologists at Iowa State University. They provide the following information and suggestions.

Think about stored grain pests before harvest

Sanitation is the most important IPM practice for storing and protecting grain. Some experts say that successful sanitation is 80% of an effective IPM program in stored grains. Removing any potential pests and their food before filling grain bins will greatly enhance any subsequent management actions.

 
• New grain should NEVER be stored on top of existing grain; remove old grain and clean bins before adding new grain.
• Clean all grain handling equipment before harvest and storage of new grain, including combines, wagons, trucks, augers, aeration fans, etc.
• Remove any grain or grain dust from inside the bins by sweeping empty bins and brushing down walls.
• Remove any spilled grain from around the outside of the bin and storage facility.
• Carefully inspect storage bins, and seal/caulk any cracks, holes or gaps that could be potential entry points for insects or rodents.
• Look for possible moisture leaks in the roof and repair if necessary.
• Remove any vegetation from within 10 feet of storage bins to discourage insects from establishing.

Empty bin treatments—use residual insecticide

The inside walls and floors should be treated with a residual insecticide after thorough cleaning. The outside walls (up to 15 feet) and outside base of grain storage bins may also be treated. The area beneath the perforated, drying floor should also be cleaned and treated with a residual insecticide. Treating empty bins is most effective when insect activity is likely ( temperatures over 60°F). Common products for empty bin treatments maybe difficult to find as labels expire (see Table 1).

Table 1. Insecticides labeled for empty grain bin treatments, intended to be applied four to six weeks before grain enters storage.

Grain cleaning and storage

Another invaluable IPM tool for stored grain pests is making sure the kernels are clean prior to storage. Dirty grain can prevent adequate airflow and uniform aeration. Uneven cooling and drying can result in hot spots that tend to favor insect development. Uncleaned grain increases the potential for spoilage since broken kernels, weed seeds and other debris often spoil at recommended moisture levels for storing grain. Excess grain dust can also form explosive aerosol dusts. Any grain protectants, top dressings or fumigations will be more effective with clean grain.

Temperature and moisture management of stored grain is vital. It is crucial that the grain mass temperature be reduced to 50 degrees F and the grain moisture is below 12 to 13% soon after storage. Colder temperatures will slow development of insects and inhibit molds, and extend insecticide residuals.

Grain protectants and top dressing

If grain is expected to remain in storage bins for over 12 months, consider using a protectant to reduce pest activity. These products are generally applied to whole grains as they are being augered, loaded, or turned into storage facilities.

A consistent rate of application is important to ensure an even distribution of the insecticide protectant throughout the grain mass. Low pressures and large droplet sizes are recommended with pressurized spray systems. These products are not highly volatile, and penetration into the kernel is limited. Do not apply grain protectants before high temperature drying of the grain because the extreme heat can cause rapid volatilization of the insecticide.

Protectants applied when temperatures drop below 40 degrees F will limit the residual effectiveness. Grain protectants applied at 13% moisture will have a greater residual life compared to applications made at 15% or greater moisture. When protectants are applied according to the label, they can be sold or fed immediately after application (see Table 2).

Table 2. Common protectants applied to grain stored longer than 12 months; applications should be made to clean, dry grain.

Sometimes, a top dressing of insecticide is recommended instead of treating the entire grain mass with an insecticide protectant. Applications should be made as soon as the grain bin is filled and the surface is level. Any disturbances to the surface may require another top dressing application. Follow label directions for these types of applications; some products recommend treating the top 10 feet of grain and other products suggest the top few inches (see Table 3).

Table 3. Top dressing insecticides for stored grain pests.

Grain monitoring also very important

Any time the grain mass is above 50 degrees F, it should be inspected for insects every two weeks. Samples should be taken from several depths and locations, paying particular attention to the grain mass surface, central core and any developing hot spots. Proper insect identification is important to determine their damage potential and control options. Purdue Extension put together a key to distinguish species . Control measures should be implemented immediately to protect grain quality.

When should you use fumigation?

 There are three options for stored grain infested with internal grain feeders (e.g., weevils and lesser grain borer): feed the grain as is, sell it at a discounted price, or fumigate. Fumigants are extremely hazardous because of the application method, and therefore, are "restricted use" products and should be applied by a licensed professional. Unfortunately, fumigant insecticides have no residual activity and grain will become susceptible to reinfestation within 72 hours.

Using proper sanitation prior to storing grain will likely prevent the need for fumigation. A storage bin with clean, whole grain is important to deter insects that feed on broken kernels and grain dust. 

Locate a licensed applicator in your region of Iowa, through this link and searching for "7c-Fumigation." For information on becoming a certified pesticide applicator in fumigation, contact the Iowa Department of Agriculture and Land Stewardship Pesticide Bureau at (515) 281-8591.