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Time to Freeze Bugs to Death

The deadliest weapon in your arsenal of bug killers isn’t a chemical – it’s the fans on your bins. They can be weaponized to cool down grain below freezing this winter, thus, killing all insects present in storage.

“Controlling grain temperature is critical for maintaining grain quality,” says North Dakota State University engineer Ken Hellevang. “Insect reproduction is reduced below about 70°F., insects are dormant below about 50°F., and insects are killed if grain is below 30°F. for a few weeks.”


Ken Hellevang’s storage strategy calls for grain to be cooled down below 30°F. or colder during the early winter months to kill insects. “Cooling grain by 10°F. doubles its allowable storage time,” he points out. “You can prevent crusting due to moisture migration by cooling grain to within 15°F. of average outdoor temperatures.”

Catch-up cooling

Actually, cooling the grain mass in a bin should have begun in November and December (as shown in the chart below). Typical postharvest aeration would have lowered the temperature of the grain mass in early winter already. Now is the time to finish the job by dropping temperatures not only to kill insects but also to arrest spoilage from mold (the risk of which can be greatly increased by an insect infestation).

“The outer layer of a grain kernel is the pericarp, or seed coat, and it provides protection for the kernel,” Hellevang explains. “If the pericarp is damaged, the kernel is more susceptible to mold growth and insect infestations. This reduces the expected storage life of the grain.” 

How long will it take to cool grain down? One rule of thumb is to divide 15 by the airflow in a bin. For example, 15 divided by an aeration system rated at .10 cubic feet per minute (cfm) airflow per bushel will cool the grain in 150 hours.

Moisture migration

Another issue in play with grain storage is moisture migration, which increases the moisture content near the top of the bin at about a 20°F. difference between the grain and the average outdoor temperature. Therefore, the grain should be cooled with aeration when you have a 10°F. to 15°F. difference between the grain and the average outdoor temperatures.

Cool the grain to 20°F. to 30°F. in northern states and 40°F. or cooler in southern states for winter storage.

Hellevang warns that bin vents could ice over when the aeration system is operated near or below 32°F. Utilize a sensor to stop the aeration fan if bin roof pressures become excessive. Leave access doors open to serve as pressure relief valves if operating the aeration system near freezing temperatures to reduce the potential for damaging the roof, he advises.

Hellevang recommends cooling grain down and then shutting off the system until the grain and outside temperatures are within 10°F. before running through another aeration cycle. “Pick a morning when you have cool temperatures, and run the aeration fan for a few hours in the early morning to push air through the cool grain in the bin,” he says.

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