Grain placed in on-farm storage this past fall and stored through the summer months of 2009 should be inspected at regular intervals for the presence of stored grain insect pests. Insect infestations may occur throughout the grain mass, on the upper surface of the grain mass, or in both areas depending on the species of insects infesting the bin. Indian meal moth is the most common insect problem found in the upper twelve inches of the grain mass where larval feeding results in areas of moist, sour smelling grain and thick webbing. If such an infestation occurs and larvae are still active, removal of the damaged grain followed by an insecticide application to the remaining grain surface may be one method of control. Pest strips hung above the grain mass inside the storage structure may help control the moth stage of this common pest.
If an infestation of various flour beetles, grain weevils, or other stored grain beetles is found infesting the grain mass, then immediate use of the grain mass or fumigations are two possible control options. If fumigation is selected, a professional fumigator should be used as the poisonous gases associated with fumigation are extremely dangerous if used improperly. The best option for management of stored grain insect infestation in summer is to immediately use the grain as livestock feed or some other use where the insects do not cause a problem in the end product.
Scouting methods differ by location in the bin. Indian meal moth infestations can generally be seen by observing the top of the grain mass from the roof access door. If no webbing or foul grain odors are found, then it is unlikely that Indian meal moths are present in high numbers. If the grain was properly leveled and treated with an appropriate insecticide after filling of the storage facility the previous fall, it is best not to break or disturb the protective cap of insecticide applied at that time. Some probing of the grain surface from the access door may be necessary to determine level of insect infestations if found. Scouting for stored grain insects in the grain mass can be accomplished by using a grain probe to collect samples through the side access panel. Grain collected should be placed in a glass jar, plastic bag, or some other container through which insects can be seen if they are present in the grain. These containers of grain should be placed in a warm area to allow the grain to warm to at least 60 degrees F or higher in order to stimulate insect activity.
Early summer is a good time to work toward the prevention of stored grain insect infestations in harvested fall grain crops. Sanitation is the main method of preventing unwanted insect infestation in stored grain. Although sanitation around storage facilities is most effective directly following filling of these facilities in the fall, early summer sanitation will also help reduce insect pest numbers later in the year. Removal or elimination of any grain scattered in the area of storage facilities will help reduce later generations of these pests. Several insecticides are labeled for use outside of grain bins, for inside surfaces in empty bins, and for addition to the grain mass at the time of filling the storage structures. All insecticides for stored grain insects have very specific labeled uses so special attention must be given when selecting an insecticide for these various uses. Some insecticides are labeled for wheat only or corn only, whereas others may be labeled for both. Be sure to read and follow all insecticide label instructions, restrictions, and precautions when using insecticides for management of stored grain insect pests.
Moisture in the grain mass is one very important factor which attracts insect pests to these structures. Charles Ellis discussed the aeration and moisture zones in on-farm grain storage facilities in the January 15, 2009 issue of this newsletter (Volume 19, Number 1). Proper aeration of the grain mass to manage moisture and grain mass temperature is essential for good insect control. Note: it often requires a week or more of aeration to move a moisture layer through and out of a grain mass depending on several factors including the volume of air moved, the size of the storage structure, and the temperature of the air being moved into or out of the grain mass.
Color images and additional information concerning proper management of common stored grain insects can be found on the Commercial AG Electronic Bulletin Board at http://agebb.missouri.edu/storage/pests/insect.htm.
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REVISED: February 29, 2012