Sealing the Harvest: PICS Bags Preserve Crops Worldwide

The Purdue Improved Crop Storage (PICS) bag has become the gold standard for low-cost, hermetic postharvest storage for smallholder farmers in developing countries. With initial funding from the former U.S. Agency for International Development, Purdue University developed a unique three-layer sack that protects harvested crops from insect damage, eliminates the need for insecticides, and allows farmers to sell their crops when market prices are more favorable—improving food security, protecting the environment, and increasing farmer income.

Originally focused on farmers in Cameroon, the PICS project aimed to reduce postharvest losses and improve the storage conditions of cowpea, a critical, high-protein staple food for the region. Postharvest losses for cowpea could reach as high as 25% (Baributsa et al. 2010), with insect damage a major cause.

One common storage pest, the weevil, can produce up to 100 offspring in a month, meaning an infested crop can be destroyed in three to four months (Wallheimer 2012). To avoid losses, farmers would sell immediately after harvest rather than storing their crops. As a result, large quantities would enter the market at the same time, driving prices down and limiting farmers’ incomes.

How the PICS Bag Works

The PICS team, led by Purdue professor and entomologist Larry Murdock, found that the combination of two high-density polyethylene liners, each 80 microns thick, inside a sturdy, woven polypropylene bag was sufficient to prevent oxygen and moisture from reaching the stored cowpea. Additionally, any insects inside the bag quickly use up their oxygen supply and die off.

Murdock later discovered that some insects do not die of suffocation but of thirst. His research showed that weevils create their own water through metabolic processes as they digest food in the presence of oxygen. When oxygen in the bag is too low, they can no longer produce the water they need.

The PICS bag’s hermetic environment also reduces rancidity, prevents discoloration, and inhibits the growth of any mold present on the crop, preventing the production of mycotoxins such as aflatoxin. For a wide variety of legumes and grains, those stored in PICS bags have shown better viability, germination, and vigor compared to other storage methods, making this also a valuable storage method for seed.

With support from the Gates Foundation, PICS bags are used in 41 countries by more than 12 million farmers in sub-Saharan Africa, South Asia, and Latin America (Purdue University 2024). Manufactured by 22 companies globally, the bags are available in 25, 50, and 100 kg capacities, with the cost for the largest about $2–$3. Farmers typically store their crop for one year, and the bags can be reused at least three times.

Since its launch in 2007, more than 50 million PICS bags have been sold, storing 15 million tons of crops (PICS Global 2026), including soybeans, mung beans, peanuts, Bambara groundnuts, wheat, maize, rice, sorghum, coffee, and cacao beans. Research on PICS bags continues, including work on biodegradable materials and monitoring insect adaptation to low-oxygen conditions.