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 Insects and Fumigation August 1999 "The Best Way to Avoid Both is to Make Sure Seeds Are Cooled Down Before They Can heat up" No one enjoys a pleasant 75- or 80-degree fall harvest season more than a producer bringing in a bountiful crop - no one, that is, except those species of insects which infest stored grain. Warm grain temperatures provide ideal conditions for insects that feed on stored grain, notes North Dakota State University extension entomologist Phil Glogoza. Some grain insect pests, like the lesser grain borer, red flour beetle, flat grain beetles and Indian meal moths, are common across the Upper Midwest, he notes, and will fly from storage site to storage site. Other insects, such as granary weevils, the saw-toothed grain beetle, mealworm beetle and spider beetle, pose the biggest threat when new grain is stored in bins that were previously infested and then not adequately cleaned. Glogoza and NDSU ag engineer Ken Hellevang encourage close monitoring of grain conditions to prevent insect problems. "Check the surface of the grain; then use a probe to check the moisture and temperature at a variety of locations. Pay attention to the look, smell and feel of the grain. Your senses can tell you a lot about its condition," Hellevang remarks. Frost or condensation on the inside of bin roofs is a clear indication of excess moisture in the grain, Hellevang notes. He suggests examining samples under good light (perhaps on a light-colored cloth) to make insect identification easier. Bringing cold samples into a heated area will increase insect activity and thus facilitate identification. Temperature is the key to controlling insects in stored sunflower and other grains, Hellevang emphasizes. As noted in the accompanying article, insect reproduction slows once the interior bin temperature drops below 70 degrees F. By 60 degrees, reproduction has ceased; at 50 degrees the insects become dormant - and most will die if the bin temperature falls to freezing and remains there for an extended period. Contributing to the threat of insect infestation is grain's proficiency as an insulator. Cereal grains have an R-value of one per inch, meaning "grain at the center of an 18-foot bin is insulated in excess of R-100," Hellevang notes. That compares to an R-20 insulation rating for a typical North Dakota home. While sunflower's insulation rating is less than that of cereal grains, it is still substantial. Fumigation - traditionally touted as the standard method of eliminating insect infestations in stored grain - is not effective or economical in many instances, Glogoza and Hellevang advise. Here's why: * Fumigants do not work well once grain temperatures drop below 60 degrees F. For a fumigant to work, it must volatilize and spread throughout the storage structure; and temperatures must be above 60 degrees for that to occur. Also, the entire bin must be at or above that temperature, Hellevang adds. "If you have a pocket that's at 80 or 90 degrees and the rest of the bin is at 40, the fumigant will volatilize in that pocket," he explains, "but insects in cooler areas of the bin won't be hit nearly as hard." An important related point: having the warm temperatures required for effective fumigation runs counter to other basic management strategy, i.e., cooling the grain to avoid insect and mold problems. * Fumigants are expensive, a hassle - and product options are very limited. (Phostoxin is essentially the only alternative left, Hellevang says.) For a fumigant to work properly, the bin must be tightly sealed to avoid leaks. * If temperatures are too cold during fumigation, remnants of the fumigant could remain in the grain. Along with making the grain dangerous to handle later on, detectable amounts of fumigant could result in rejection of the grain at the elevator. The best strategy, Glogoza and Hellevang emphasize, is to avoid situations under which insect populations can develop. Even if the binned crop is cooled over winter, a large population of dormant insects will be prepared to "explode" upon the arrival of warmer spring temperatures. Cooling the binned grain down as quickly as possible after being placed into storage is the most effective way to keep the troublesome bugs at bay.  Back to Harvest/Storage Stories Back to Archive Categories
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