Grain bin

While insects are dormant, farmers can plan their strategy to regulate bin temperatures and move long-term storage early  — before pests can begin to feed on grain this spring.

The first few weeks of January are shaping up to be warmer than normal, and for farmers storing their grain, that means a little extra attention is needed.

While typical cold winter months see many pests, such as weevils and borers, go dormant, a winter warm spell could wake some and become a problem.

But once the grain is in the bin for the winter, there isn’t much farmers can do.

“There’s not really anything preventive-wise you can do right now because if the bugs are there, they are dormant anyway,” said Mike Moellenbeck, vice president of Grain Marketing for River Valley Cooperative.

“When you see a warm-up next spring, just be aware that (old crop) inventories are the most likely to start out having insect problems and should be the first ones to get moved.”

Moellenbeck said, if possible, start moving the grain that’s been sitting the longest before the seasons change.

Typically, the most pest activity occurs when temperatures inside the grain bin reach 70 degrees, said Mike McDowell, regional sales manager for Brock Grain Systems, noting that most insects will remain dormant at 50 degrees or below.

“Making sure that you have the grain cooled down to the correct temperature will make it least likely to see spoilage or insect growth in the bin during the storage season,” McDowell said. “In a warmer winter, farmers will want to monitor their temperature cable systems, if they have them in their bins, to see if there is a rise in temperature.”

South Dakota State University Extension field crop entomologist Adam Varenhorst said in an article on the university’s iGrow website that stored grain with a temperature above 55-60 degrees should be inspected each week, and every two weeks when the temperature is below 55 degrees.

During the winter, insects will move to the center of the bin, so sampling at that location is important.

There are several species of insects that feed on stored grain, he said. These insect pests can be grouped based on whether they are internal feeders or external feeders. Internal feeders feed within the kernels while external feeders will consume grain dusts, cracked kernels and other grain debris. 

Weevils are generally given the most attention because they are among the most destructive pests of stored grain. The larvae of grain weevils develop within the kernels, and when infested grain is left undisturbed for long periods of time, they can cause nearly complete destruction, Varenhorst said.

The lesser grain borer is a pest of a wide variety of grains. The larvae and adult of this pest are damaging.

The stored grain pests that are external feeders are present in the grain because grain dusts, cracked kernels, or other grain debris was present and is a viable food source, Varenhorst said.

Similarly, to internal feeders, the best management for these insects is prevention. The presence of fungus feeders indicates that the grain is moldy. Proper aeration and grain cleaning can prevent most infestations caused by external feeders.

Varenhorst noted that once an infestation is detected, there are only a few options: move the crop and have an insecticide applied, feed it to livestock as-is, sell it at a reduced rate or fumigate it.

It is not necessary to treat grain with a protectant insecticide prior to binning, but he added that one “should be applied to grain that is expected to be stored for more than one year.”

Tom Miller, a grain handling equipment salesman at Eldon C. Stutsman, Inc. in Hills, Iowa, said there are few chemicals that can be sprayed inside a bin.

“Naturally, your pests are going to work from the bottom to the top,” he said. “… If someone throws in diatomaceous earth in there and spreads that around on the first layer of grain, that should help.”

Diatomaceous earth is soft sedimentary rock that is crumbled into a fine white powder. It is abrasive to pests, causing them to be cut by the rock and eventually die.

Miller added that the biggest thing farmers can do to prevent pests from being attracted to bins is taking care of the crop through temperature control and regulated moisture levels.

“You have to have something that is going to draw them in there,” Miller said. “Good, dry corn is probably not going to attract the pests. It’s when you start getting the corn to go out of shape, or out of condition, where it’s going to start fermenting and the odor is going to attract the bugs.”