INITIAL CONDITION DETERMINES
QUALITY OF STORED GRAIN
David P. Shelton, Extension Agricultural Engineer
Keith J. Jarvi, Extension Assistant, Integrated Pest Management
David D. Jones, Associate Professor, Biological Systems Engineering
Grain quality does not improve in storage. At best, the initial quality can only be maintained. On the other hand, if proper management is neglected, the entire bin of grain could wind up as a worthless, moldy, insect and rodent infested mass.
Since little can be done about weather influences on grain quality while the crop is growing, harvest is the time to assure that only high quality grain goes into clean storage bins. First, clean-up the bin site. Spilled grain and feed accumulations near bins are frequently overlooked as potential sources of migrating insects, as are dusts created by feed grinders, feed left in self feeders, etc.
Leftover grain should be removed from the bin, and the walls should be swept and vacuumed. By removing the fan, and using a grain vacuum, much of the accumulated debris can also be removed from beneath perforated floors. The bin should then be fumigated with chloropicrin as a "clean-out" fumigant. (Chloropicrin is a Restricted Use Pesticide and requires gas monitoring devices and respirator protection.)
If long term storage (over 10 months) is planned, consider treating the cleaned bin with protective insecticides, 2 to 3 weeks before new grain is added. Apply the spray to the point of runoff to as many surfaces as possible, especially joints, seams, cracks, ledges, and corners, including outside the bin at the foundation and near doors, ducts, and fans. Malathion, methoxychlor, Tempo, Reldan, or diatomaceous earth may be used for this purpose. (Only use Reldan when sorghum is to be stored.) Do not apply Tempo or methoxychlor directly to grain. As with all pesticides, read and follow label directions during handling, mixing, and application. NOTE: Do not spray bins where soybeans will be stored. Stored soybeans rarely experience insect problems and few insecticides are labeled for use on soybeans.
Before any grain is harvested, all grain handling equipment including augers, combines, trucks, and wagons should be cleaned and old grain residues removed. Combines should be adjusted to minimize grain damage and maximize removal of fines and other foreign material. Many of the common grain insects are secondary feeders - feeding only on broken or cracked kernels and other materials, not sound kernels. Be especially careful when harvesting and handling grain from stressed crops because this grain is more easily damaged.
Operate augers at full capacity to reduce wear and grain breakage. With variable incoming flowrates, reducing auger speed can keep the auger operating at full capacity. Another option is to add a hopper over the auger intake, keeping it full. Be sure that all safety shields and auger intake grates are kept in place and in good working order.
To reduce the incidence of molds and insects, cool and dry the grain immediately after combining. Deterioration of grain quality occurs rapidly at higher moistures and temperatures. For example, grain held continuously at 75o F and 25% moisture content will deteriorate more in four days than 15% moisture grain held at 60o F would in 250 days. Warm, moist grain is also more prone to problems with molds and insects.
Moisture content of the grain going into storage is critical to assuring that quality can be maintained. Recommended moisture contents depend on the length of time that grain will be stored, and are given in Table 1. These recommendations assume the grain is high quality and aerated to control temperatures and moisture migration. Reduce the recommended moisture contents by 1 percentage point when storing low quality grain. This includes immature grain, severely cracked and damaged grain, and grain subject to previous insect or mold activity. Also reduce the recommended moisture contents by at least 1 percentage point for grain in temporary or emergency storage.
|Table 1. Maximum recommended moisture contents for properly managed, high quality, aerated grain.|
|Storage Period||Corn and Sorghum||Soybeans|
|Fed by April||18%||13%|
|Marketed by June||15.5%||13%|
|Up to one year||14%||12%|
|Over one year||13%||11%|
Grain going into a bin should be clean. Broken kernels, foreign material, and fines will create additional problems in stored grain, particularly when they accumulate in concentrated pockets. Besides being more attractive to some insects, broken kernels are more susceptible to spoilage than unbroken ones. Also, airflow from drying or aeration fans tends to go around pockets of fines so they cool and dry more slowly. These pockets often develop into hot spots that result in spoiled grain.
The most effective way to remove broken kernels, fines, and other foreign material is to use a high-capacity rotating grain cleaner. If this is not possible, a power spreader can be used to minimize concentration of fines, although a "doughnut-shaped" accumulation of material often occurs in the bin. If a power spreader is not used, install a grain cone in the bin to break up the inflow of grain and partially spread the fines.
More grain goes out of condition because temperatures are not controlled than for any other reason. When first put into storage, grain should be cooled to the prevailing temperatures at that time. While in storage, temperatures should be maintained within 10 to 15o F of the average outside air temperature. Temperatures below 50o F will prevent insect feeding and reproduction.
As grain is being augured into storage, apply a liquid or dust grain protectant if the grain will be stored for 10 months or more. Use either Actellic (corn and sorghum) or Reldan (sorghum only). (Malathion is still available as a protectant, but is not recommended due to heat degradation and insect resistance.) Power spray applicators are preferred over gravity drip applicators because they provide more uniform coverage, giving better insect control.
Treating when the grain is above the recommended moisture for long term storage and the grain temperature is above 90o F will limit the effectiveness of the insecticide, as the combination of moisture and temperature will increase the breakdown rate. If grain must be treated when it is warm, it should be cooled with an aeration system as soon as possible. Operation of the aeration system will not remove the protectant from the grain.
After the grain has been leveled in the bin, topdress the surface with both Dipel (corn, sorghum, or soybeans) and malathion (corn or sorghum), or Actellic (corn and sorghum), or Reldan (sorghum only), or diatomaceous earth. Dipel works against Indian meal moths while malathion is needed for beetle control. Actellic and Reldan control both types of insects. Do not treat soybeans with malathion, Reldan, or Actellic. If Indian meal moths have been a problem in the past, use Vapona resin strips (1 strip per 1,000 cubic feet of air space) in the bin space above the grain.
Stored grain represents a major investment. Precautions taken as the grain is put into storage can pay dividends later by helping to assure that quality is maintained.