Americans Consume Over 4 Billion Gallons of Popcorn Annually – Learn How It Is Best Protected!
Systemized farming created new opportunities for our ancestors to grow and stockpile food. As populations expanded and technology became readily available, yields also increased. Eventually a single year’s harvest was more than enough to feed a family, forcing commodities to be stored for an extended period of time, but also readily available in the case of famine. This created a never-before-seen paradise for opportunistic insects, like weevil and Indian meal moths, which migrated from the crop fields to invade these stagnant storage sites. There they had perpetual warmth, no natural predators, and virtually endless food supplies.
With this invasion came undesired destruction and communal disgust; so, commodity security was prioritized. Fumigants became a widespread mechanism for damage prevention and margin sustainability. Pesticide labeling of fumigants allowed different techniques for treating storage structures, but to this day the most effective methods are still debated over within the grain industry. While customer needs, safety recognition, and site-specifics are taken into account during each fumigation, it is difficult to compare techniques without multiple applications under similar conditions.
FSS performed preliminary phosphine fumigation studies on bolted-steel popcorn bins and analyzed the gas concentrations throughout the process. Popcorn is unconventionally stored in comparison to other kernel grains, like wheat and soybeans. Popcorn’s fragility restricts it to a certain humidity range during storage, with a small degree of freedom. Humidity can alter its “popping” capabilities, affecting the kernel’s size and fluffiness upon heating. The higher it pops, the less kernels it takes to fill your movie theater bucket! Therefore, popcorn is often stored in smaller bins that allow easier temperature and conditioning parameters. This makes it hard on a fumigator, who must effectively contain gas in leaky bins.
Bin fumigations typically consist of probing aluminum phosphides into the top of the grain mass, along with sealing and recirculation of the gas throughout the structure. This study compared data from over 150 popcorn bins, held at an average temperature of 70oF. Two different sealing practices were performed in parallel. The first method consisted of covering the top of the mass with a plastic tarp encompassing the fumigant and popcorn.
Headspaces above the tarp are normally fogged with an insecticidal fog to kill any insects that may reside on the walls. The alternative method incorporated treating the headspace with the gas fumigant and required sealing the top of the structure from the exterior, including eaves, vents, fans, and hatches.
The bottoms of the bins were all sealed identically, and fumigant was accounted for the difference in total volume.
Both techniques come with their own safety concerns and difficulties. Depending on the bin size and customer desires, a fumigator must decide which method to use. This study looked at the levels of phosphine that were achieved throughout the 3-day fumigations. Some bins were sealed up by tarping while others were sealed from the exterior.
The goal was to exceed 300 ppm for 3 consecutive days as shown. This typically ensures a kill of all insect life stages. The tarping method showed an average of 983 ppm over the 3-day period while exterior sealing only generated an average of 525 ppm. Even more, exterior sealing usually required additional fumigant throughout the process to maintain threshold levels, which ultimately slightly inflated the averages. Trials indicated about 33% more fumigant was added to bins sealed from the exterior to account for gas loss (figure not shown).
Choosing the correct method can often be a tug-of-war between the fumigator and the client. Understanding the differences between these two methods allows the applicator to provide the best procedure for a given situation. Beyond this study, similar results are seen between these two methods for silo fumigations of all sizes – even those holding up to 1 million bushels! Before choosing a method, always consider the pest of interest, the type of fumigant being used, and the ease of access, but most importantly the safest procedure for an effective treatment. REMEMBER THAT NO DEAD INSECT IS WORTH THE COST OF AN INNOCENT LIFE!
- Acknowledgement Fumigants & Pheromones Newsletter Issue 125