Timely and effective sealing of Purdue Improved Crop Storage (PICS) bags

Purdue Improved Crop Storage (PICS) bags are a hermetic grain storage system originally designed to reduce postharvest crop losses of small-scale farmers. The PICS bag consists of two high-density polyethylene inner liners (bags) fitted inside a third woven polypropylene bag. This multi-layered bagging system has been shown to suppress growth and survival of insects and pathogens. Recently, PICS bags have begun to find a wider circle of users, including large-scale grain storage agencies. PICS bags as used by farmers have traditionally been closed by a twist-tie method, which includes twisting the lip of each liner individually, folding the lip over, and tying with a cord. This method is not only time and labor intensive, but also may affect the integrity of the plastic liners. We conducted a study to identify potential alternatives to the twist-tie method. We used 50 kg capacity PICS bags filled with 30 kg maize and infested with 100 adult maize weevils. We tested four bag closure methods; all liners twist-tied (TT), inner plastic liner fold-tied and the middle liner rolled onto itself (IF), both plastic liners fold-tied together, (BF), and both plastic liner fold-tied separately (FT). The outer woven bag was twist-tied in all cases. Results showed that respiration of insects caused the oxygen in all bags to fall after closure. This indicates that all closure methods were equally effective in sealing the bags. The BF method was more time and labor efficient and thus can be used as an alternative to the traditional twist-tie procedure.