David Owens, Extension Entomologist, owensd@udel.edu
I get asked about grain pests about once a year, just enough to keep them on my radar but not enough for me to be very familiar with products and rates. I rely heavily on other extension resources. The below information was borrowed heavily from Purdue: https://extension.entm.purdue.edu/publications/E-66.pdf. Our most common stored grain pests are Indian meal moth, granary and maize weevil, and sawtooth grain beetle. It’s important to get bins ready properly and treated so that these insects do not cause problems.
The first step is to clean the bin well. Remove debris that insects may be hiding in before loading new grain into the bin. This not only includes the bin itself but also any transportation vehicle or equipment including augers. Pay attention to false bottoms and air handling systems. Remove debris from the site. Remove vegetation from within 10 feet of the bin.
Second, treat the bin ahead of time. Surfaces can be treated with malathion or pyrethroids. If prolonged storage is anticipated or you’ve had problems recently, Purdue recommends fumigating with chloropicrin to the bin floor. If new grain is added to old, fumigate with aluminum phosphide.
While grain is loading into the bin, it can be treated with a protectant insecticide. Read labels carefully, not all are labeled for all grains; some are only labeled for corn, some only for small grains and a few labeled for soybean. Please note that chlorpyrifos is no longer available for grain storage. It’s also important to keep notes of what insects have been in the bins before, For instance, B.t. is only effective on caterpillar pests, not beetles. If using a protectant, do NOT use before heated drying, the heat will greatly lessen the efficacy and residual of the insecticide.
After grain is binned, sample it every couple of weeks when the temperature is above 55 degrees. Some treatments can be ‘capped’ – applied to the top surface of the grain after binning but is not effective on all pests. If grain weevils are present, fumigation is the only recommended mitigation.