Bins should be inspected on a regular basis for insects, hot spots, mold growth, or any "off odor." As a general guideline, bins should be sampled twice a month April through November and once a month December through March. Regular inspections will reduce the chances of pests becoming established. Take all necessary safety precautions. Bins should be easily accessible and all unloading equipment should be turned off. Be aware of any pesticides applied to the grain, undissipated fumigants, bridged grain, grain dusts, and high temperatures. WORKING IN TEAMS IS THE BEST POLICY, WITH AT LEAST ONE MEMBER ON THE OUTSIDE OF THE STORAGE FACILITY.
Samplers should be alert for off odors, crusting, temperature differences greater than 10°F, visible water vapor, sprouting grain, exterior bin conditions and signs, uneven snow melt or frosting, condensation, discoloration, fecal matter (birds, rodent, and insect), and birds (insect feeders).
Use a probe (grain trier) or scoop to collect the samples. Take 5 to 10, one-pint samples from various areas over the grain surface. Using a compartmentalized grain trier will allow the sampler to determine differences in grain moisture, insect populations, temperature, and grain quality at different depths in the grain mass. Label samples so problem areas within the bin can be identified. Sampling at different depths will greatly increase the chances of finding trouble spots before a large area of grain is damaged.
Grain temperature should be determined as soon as possible after the sample is taken to achieve the most accurate results. Temperature differences in the range 10 to 15°F indicate a potential problem. Usually aeration will correct the temperature difference. After corrective measures are taken, further sampling is suggested to ensure the problem has been corrected.
When sampling for insects in cool grain, samples should be warmed. Warming will increase the activity of the insects, allowing the sampler to easily spot the pests and determine if the insects are alive. Individual samples can be placed in labeled plastic bags to guard against contamination. Each sample should be placed on a sieve, which will hold the grain while allowing the pieces (fines), insects, and small debris to pass through. If insects are present, save them for identification, estimate the abundance, and determine the distribution. Pest identification is crucial when selecting a control measure. For example, several species of insects feed on fungi. Their presence indicates a moisture problem. Control of the insects with pesticides can be achieved without correcting the primary problem.
Another method of sampling involves using a grain probe trap. This trap consists of a perforated plastic tube with a funnel collector on the bottom. Traps are inserted in the grain mass and marked with colored string, which allows them to be retrieved. Traps are retrieved after 24 hours and are more efficient than probing and sieving for beetles, but they do not adequately detect moth larvae.
Trouble spots can also be identified using a metal rod. Insert the rod into the grain and allow it to remain for several moments. Hot spots can be detected by running your hand down the rod after removing it from the grain. If temperature differences are sensed, investigate these areas further to determine the reason for the difference in grain temperature.
Accurate records should be kept so changes over time can be detected. Records can be used to refine a management strategy for your individual operation.
Wheat, Rye, or Triticale-One live insect per quart sample
Corn, Sorghum, Barley, Oats, or Soybeans-One live weevil or five other insects per quart sample
If these thresholds are exceeded, fumigation is suggested. However, if the weather is cool, fumigation should be delayed. Fumigation effectiveness is greatly reduced under cool conditions. For conditions that do not favor fumigation, the grain mass may be cooled to below 60°F if possible. At temperatures below 60°F, insects are for the most part inactive. When temperatures permit, fumigation should be considered.
