A warmer-than-normal fall may contribute to higher insect populations in your on-farm storage systems.
By Wayne Bailey, University of Missouri Extension Entomologist
If grain bins and handling equipment were not sanitized prior to grain fill and the grain was moved to storage without receiving a preventative insecticide application, insect infestations can develop in as little as 3 to 6 weeks following initiation of grain storage.
In normal years, cool fall temperatures usually allow the stored grain to be cooled to 50 - 55 F, which causes any insects infesting the grain to become inactive.
The high value of grain crops held in on-farm storage can best be protected by implementation of a monitoring program for detection of insect infestations and other problems within storage structures. Producers should monitor stored grains regularly to assess grain moisture, temperature, and determine whether insect pests are present.
Grain should be monitored a minimum of once each month during the winter months of November through April and at least twice per month during the summer months of May through October. Areas of the grain mass most frequently infested include the grain surface and central core. Special attention should be given to these areas when sampling, but other areas of the grain mass should not be ignored.
Scouting methods differ by location in the bin and the specific type of insect present. To determine if insects are present, producers should visually inspect the top of the grain mass by looking through the roof access door.
A sour smell, grain clumped together, condensation present on the inside surface of the bin roof, webbing on the grain surface, or the presence of insect larvae, adult beetles or moths all indicate the presence of an insect infestation. If an insect infestation is found on the surface of the grain mass and webbing is present, this usually indicates the presence of Indian meal moth.
As this insect only damages the upper 12-14 inches of the grain mass, removal of the webbing and damaged grain along with an application of an appropriately labeled insecticide are recommended (See section 2B of summary for labeled insecticides). Pest strips (dichlorvos or DDVP) hung above the grain mass inside the storage structure may help prevent Indian meal moth infestations by controlling the moths of this common pest as they enter the storage structure. If no insects, webbing or foul grain odors are found during the inspection, then it is unlikely that Indian meal moths are present in high numbers.
If the grain was properly leveled and the grain surface treated (capped) with an insecticide after filling of the storage structure the previous fall, it is best not to break or disturb the protective cap of insecticide previously applied at that time.
An inspection of grain from the interior of the grain mass is also needed. Monitoring of the grain mass is best achieved through the side access panel by using plastic tube traps, probe traps, and sticky pheromone traps. These traps are inserted into the grain mass for a certain period of time and then retrieved.
These types of traps will attract insects and help determine the kind and number of insects present. If traps are unavailable, a quick, but less accurate method of sampling the grain mass for insects, can be accomplished by direct observation of grain removed from the side door using a grain probe.
Deep probes should be collected from several locations in the bin with the collected grain placed in a quart 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.
Although there are no reliable thresholds for most insects found in stored grains, it is usually considered that if insects are found in the 1 quart samples of grain collected, the grain content of the bin should be either quickly used or treated (fumigated) to kill insects present in the grain and prevent excess loss of grain quality when stored at summer temperatures.
All insecticides for stored grain insects have very specific labeled uses so special attention must be given when selecting an appropriate insecticide. Some insecticides are labeled for use in empty grain bins, but are not labeled for use on grain. Some insecticides are labeled for wheat 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.