Modified Atmospheres

It can feel like insects are as plentiful as the air we breathe, especially in stored grain. “Invisible” yet ever-present, we often fail to appreciate the impact of both forces until it’s too late. But, could you use the latter to control the former? The idea may sound silly, but let’s try to breathe some life into it.

A CHANGE IN ATMOSPHERE. Modified atmospheres (MAs) are any sort of pest management that changes the balance of oxygen (O2), carbon dioxide (CO2) and nitrogen (N2) from their atmospheric concentrations. This change can be passive or active, but all methods have the same goal. Controlled atmospheres (CAs) flush out O2 with N2 or CO2. In an N2 flush (delivered by canisters), O2 drops from 20% atmosphere to less than 1%. Meanwhile, during a CO2 flush, the goal is to raise CO2 concentrations to 30 to 70% atmosphere, with the exact percentage dependent on the delivery method selected (e.g. CO2 canisters, gas exhaust, dry ice, etc.).

A third method, hermetic storage (HS), also targets high CO2/low O2, but, instead of actively changing gas concentrations, HS uses respiration of the pests (insects, molds, etc.) to drive this process. HS containers can come in a variety of forms and shapes (i.e., silo bags, triple-layer bags, cocoons, silos) as long as they provide an airtight seal.

RANKED AGAINST ALTERNATIVES. Each method has its own benefits and limitations. As a group, MAs are equally effective at controlling pests as pesticides and chemical fumigants. They can be applied in the same structures that fumigants can but without risk of undesirable damage to the structure or chemical residue. CAs can also effectively control pests after similar exposure periods as chemical fumigants, such as phosphine gas. Lastly, because of its seal, HS is also great for controlling moisture migration, limiting mold growth.

CAs, however, may have larger up-front costs than comparable fumigant treatments because of the need for an airtight seal and lower market demand. Low temperatures also negatively impact effectiveness, extending exposure periods by days (CO2 treatments) or weeks (N2 treatments). HS may seem like a less-expensive option; seal your bin or store in silo bags, and the insects take care of themselves. But, HS works best for grain stored for a few months to a year. If you need to control a massive problem quickly, it may not be the best option. Lastly, like chemical fumigants, MAs provide no residual control after treatment, meaning pests can move in immediately if preventative measures are not in place.

EVIDENCE OF SUCCESS. Even with these limitations, MAs have been successful for different sectors of agriculture. The Purdue Improved Crop Storage (PICS) bag has been bringing HS to African farmers since 2009. The clean grain and dependable food supply have helped transform the economic outcomes of the communities in which it is available. And, these benefits can also be enjoyed at industrial scales. Countries with advanced agricultural sectors, like Argentina and Australia, use hermetic grain bags in addition to sealed silos for controlling grain pests in storage with great success. So, using this method of pest control in the United States is not a leap in logic.

Wherever there’s food, there will be insects to eat it. But, that doesn’t mean we have to keep using the same tricks to fight them. MAs are a credible alternative to chemical treatments that can have a real impact on U.S. agriculture. While expensive up front, they could make significant differences in the effectiveness and cost of grain storage in the future. So, next time you check your bin, maybe you should grab a caulk gun and start sealing.

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