Last month, our writer Mercy Kahenda wrote a piece on a special silo that keeps weevils at bay and there was a lot of interest from grain farmers. So this week, I will delve deeper into the Hermetic sealed metal silo (grain storage silos)

Weevil infestation, especially from the larger grain borer pest (commonly referred to by farmers as ‘Osama’) contributes to more than 40 per cent loss of farmers’ maize produce.

This adversely affects the livelihoods of smallholder farmers by decreasing saleable harvest, reducing their ability to manage changing market prices and their income. After harvest, many farmers are faced with a problem of storing their yields safely. Sadly, farmers are not aware of the existing post-harvest solutions. They continue to store grains in regular bags, leading to high quantities of food loss.

Due to lack of enough stores and storage facilities, some farmers store their produce — mostly maize, beans, cowpeas — in bags, sheds and under their beds, which are not ideal places to keep the produce safe from pests and other contaminations. They sometimes use pesticides, which, if not used according to recommended doses, can cause negative health effects.

Hermetic grain storage bags or Purdue Improved Crop Storage bags present a realistic solution to grain storage. Hermetic storage works by allowing the insects to naturally respire and exhaust oxygen levels in an airtight environment to the point where they cannot survive. Insecticide or fumigation is not necessary. However, the grains must first be properly dried to about 12–14 per cent moisture content.

Larry Murdock, an entomology professor at Purdue University in Indiana, came up with a bag that looks and functions a lot like the polypropylene bags that farmers already use, but it consists of three separate plastic layers that make it both tougher and able to keep out oxygen when each layer is tied closed with a cord.

Strong points

The bag is made of two liners of high density polyethylene which is impermeable and one layer of double woven propylene sac. The bags are airtight where the two polyethylene liners if properly sealed, cut off air supply from the outside. The oxygen inside the bag is used during metabolism and carbon dioxide released accumulates inside the bag. Before storing crops, one should ensure that the yields are very dry and clean. Remove all the debris from the harvests. Drying before storage may help to reduce the initial rate of infestation.

After preparing the harvests, the farmer should take the three bags apart and check the two inner bags for holes and tears. Pour a small amount of crops into the inner bag. This will help to easily insert the first bag into the second. Insert the first polyethylene bag into the second bag and make sure that there are no air pockets at the bottom. Insert the two polyethylene bags into the woven polyethylene bag, fold over the top of the woven polyethylene bag and do the same with the second bag as well. Fill the inner bag with more grain and shake gently to reduce the pockets of air. Make sure there are no grain gets between the bags. Fill the bag far enough so that a lip remains for tying and pack the grain tightly to remove air. Hermetic bags are effective in controlling pests like larger grain borer, bruchids and others. Quality is preserved (no germination, no mold.

Lack of oxygen would not allow mold to grow). Opening and closing the bags during storage does not reduce the efficacy of the technology. Dr Ogema of Masinde Muliro University of Science and Technology recommends limited opening frequency (once per month) for smallholder farmers who may need grain for home consumption and therefore are able to access it when needed. Hermetic grain storage is appropriate method for many subsistence farmers.

It eliminates the need for insecticides, which are costly and often inaccessible. Misuse of insecticides by farmers is common and can cause health and environmental problems. The chemical-free storage keeps food fresh and free from pests for more than a year after harvest. On average, farmers use the bags three to five times before they wear out, and are re-purposed in inventive ways.

The new storage technology guarantees food security as farmers can use them to keep dried food over long periods of time rather than selling off their harvests cheaply in fear of pest damage and buying them back from traders at higher prices at times of scarcity.

Selling chemical-free produce, especially across the borders, will enable farmers to compete favorably on the international market. The bags can also be adopted by institutions like schools, colleges and universities that purchase produce in plenty.

The writer is a consultant/expert on sustainable agriculture and agricultural innovations