Reducing Post-Harvest Losses In Maize: Storage Solutions That Work
On a cool June morning in Hurungwe, the harvest yard at Mai Chuma’s homestead is quiet. The fieldwork is finished; the cobs have been picked and shelled. White grain lies spread on old fertiliser bags, drying in the sun. Nearby, three shiny metal silos stand against the wall of a brick storeroom — her insurance against hunger and wasted effort.
Like thousands of smallholders across Zimbabwe, she knows the bitter experience of watching a good maize harvest disappear in the granary. Insects, mould, rats, and moisture can destroy a crop that survived drought, armyworm, and high input costs. Observers estimate that smallholder farmers lose a large share of their maize after harvest each year — grain that never reaches the family pot or the market.
Yet much of this loss is preventable. With better drying and simple, proven storage technologies, farmers can keep more of every bucket they harvest, supporting household food security and the income goals set out under Zimbabwe’s National Development Strategy 1 (NDS1) and AU Agenda 2063.
Why Is Maize Lost After Harvest?
Post-harvest losses in maize usually come down to four culprits: moisture, insects, rodents, and moulds such as those that produce aflatoxin. Understanding how each one operates is the first step towards stopping them.
Moisture: The Silent Starter Of Trouble
Maize must be properly dried before it goes into any storage structure. Specialists recommend a moisture content below about 13% for safe storage. Above this level, grain heats up, sweats, and becomes a perfect breeding ground for moulds and storage insects.
Under pressure to clear fields or repay debts, many farmers shell and bag maize too early. Grain that still feels slightly soft when bitten — rather than cracking with a clean, crisp sound — is not dry enough. Once this maize is bagged and stacked in a dark corner, moisture damage begins quietly, long before any insect is seen.
FFA Explainer:
Grain moisture content is the amount of water inside the grain. High moisture makes grain “alive” — it respires, heats up, and allows fungi and insects to grow. Low moisture slows biological activity and keeps the grain stable. Farmers use simple tests like biting or shaking grain to judge dryness when they don’t have meters.
Insect Infestation: Weevils And Grain Borers
The larger grain borer (Prostephanus truncatus) and the lesser grain weevil (Sitophilus zeamais) are the main storage insects attacking maize in Zimbabwe. They often enter storage at low levels — a few eggs or adults left in old bags, cracks, or unclean stores.
Under warm conditions, these populations can explode. The larger grain borer can multiply rapidly, turning hard grain into dust and hollow husks within months. By the time a family needs that maize in August or September, a full granary can be half-empty or filled with powder and insect droppings.
Rodents And Birds: Small Animals, Big Damage
Traditional granaries with open sides or poorly sealed doors are easy targets for rats, mice, and birds. A single rat can eat or contaminate many kilogrammes of grain in a year, and its urine and droppings add moisture and disease risks.
Aflatoxin: The Invisible Danger
Aflatoxin is produced by Aspergillus moulds that grow in moist, warm grain. It cannot be seen or tasted, yet it can make people and livestock sick. Formal buyers reject aflatoxin-contaminated maize, and regular consumption poses serious long-term health risks.
Prevention is far easier than cure: keep grain dry, cool, and clean from the field all the way through storage.
What Storage Solutions Actually Work For Smallholders?
Zimbabwean farmers are not short of ideas. From traditional cribs to modern hermetic bags, a range of solutions — many low-cost — can dramatically cut post-harvest losses when used correctly.
Can Traditional On-Cob Cribs Still Help?
Storing maize on the cob in ventilated cribs is a long-standing Zimbabwean practice, particularly in districts such as Gokwe, Mt Darwin, and Guruve. When well constructed, these structures can work reasonably well for short-term storage of two to three months.
Effective cribs should:
- Be raised off the ground on strong wooden or metal legs.
- Include rat guards on the legs to stop rodents climbing up.
- Have open sides made from poles, wire, or slats to allow maximum airflow.
- Be shaded, to reduce direct heating and cracking of grain.
However, traditional cribs struggle to protect against the larger grain borer and rodents over longer periods. For farmers aiming to hold grain for six to eighteen months, more secure solutions are needed.
How Do Metal Silo Bins Protect Maize?
Hermetically sealed metal silos — sometimes called “family silos” — have been promoted across the region with support from agencies like the FAO. In Zimbabwe, they’re manufactured by local artisans and can be ordered through extension offices such as Agritex or development organisations like ACDI/VOCA.
A typical smallholder silo:
- Is made from galvanised metal sheet.
- Holds between 100 kg and 1,000 kg of grain.
- Has a tightly sealing lid and outlet.
Because the silo is airtight, insects inside consume the limited oxygen and die within days. No new insects can enter, and rodents can’t chew through the metal. When kept under shade, the silo also limits temperature changes, helping to preserve grain quality.
Approximate costs reported by field projects suggest a 100 kg silo may cost around US$20–30, while 1,000 kg units can range in the US$100–150 bracket. With a life span of many years, farmers and extension officers often describe these silos as one of the best long-term investments for households that regularly store maize.
To use a metal silo correctly:
- Dry grain thoroughly to safe moisture before filling.
- Consider mixing in a little dry ash or diatomaceous earth to help kill any insects present.
- Fill and seal tightly.
- Avoid opening frequently, which lets in fresh air and insects.
“Before the silo, I could not keep grain past June without weevils taking over,” said a farmer from Zvimba who was supported by a church-based project to acquire silos. “Now we are still eating our own maize in October.”
What About Hermetic Bags?
Hermetic storage bags — often sold under brands like GrainPro or PICS (Purdue Improved Cowpea Storage) — provide a more portable option. They’re heavy-duty, multilayer plastic bags designed to be airtight when tied correctly.
These bags:
- Typically hold around 100 kg of maize.
- Cost less per unit than metal silos.
- Use the same oxygen-limiting principle to kill insects.
They’re available in many agri-supply shops and sometimes through NGO-supported programmes. Farmers like hermetic bags because they’re easy to adopt and can be used in existing storerooms or houses.
However, they’re more vulnerable to:
- Punctures from sharp objects.
- Gnawing by rats and mice if left unprotected.
To protect them, store hermetic bags in a rodent-proof room, off the ground, and away from nails or rough surfaces.
Is Chemical Treatment Still An Option?
Many Zimbabwean farmers are familiar with Actellic Super Dust, a grain storage insecticide based on pirimiphos-methyl and permethrin. It’s widely used because it’s relatively affordable and available through rural shops.
When used correctly, one small sachet (often around 150 g) is mixed into a 90 kg bag of maize as it’s filled, coating the grain and providing protection against weevils and grain borers for up to about six months.
Safety guidelines are essential:
- Use only registered grain storage chemicals.
- Wear gloves and avoid inhaling dust while mixing.
- Keep chemicals away from children and food preparation areas.
- Wash or winnow grain thoroughly before cooking.
- Don’t treat grain that will be consumed immediately.
Many extension workers now encourage farmers to combine safer, non-chemical methods like hermetic storage with careful chemical use where necessary.
Do Traditional Methods Like Ash And Chillies Help?
Long before commercial insecticides arrived, farmers used materials at hand to protect stored grain. Two methods remain common:
Wood Ash
- Clean, cool ash from cooking fires is mixed with dried grain at roughly one part ash to ten parts maize.
- The ash scratches and dries out insects, making survival difficult.
Dried Chillies
- Dried red chillies are mixed through the grain or layered between maize in storage containers.
- The strong smell and compounds in chilli can deter some insect pests.
These methods are low-cost and can extend safe storage time, especially where cash for other technologies is scarce. Still, they’re generally less reliable over long periods than hermetic storage or properly applied chemical treatments.
What Are The Golden Rules Of Maize Storage?
Whatever storage technology a farmer chooses, a few universal rules make the difference between success and loss.
- Dry thoroughly before storage. Sun-dry shelled grain on a clean tarpaulin or plastic sheet for three to five days. Bite a grain: if it crushes cleanly with a sharp click, it’s usually dry enough. If it feels soft or chewy, keep drying.
- Clean the storage area. Sweep out old grain, remove spider webs and rubbish, and, where possible, disinfect walls and floors. Leave the room empty and closed for a few days before filling.
- Don’t mix old and new grain. Old stocks may already carry insects. Mixing them with new harvest spreads infestation quickly.
- Monitor monthly. Smell the grain for mustiness, listen for insect rustling, and feel for clumping or heating. Early signs allow quick action — sun-drying again, sieving, or treatment — before damage becomes severe.
- Sell or process risky grain. If maize is too moist or already infested, it’s safer to sell quickly or process into meal or stockfeed than to attempt long storage.
Extension officers linked to the Ministry of Lands, Agriculture, Fisheries, Water and Rural Development, and organisations such as the Zimbabwe Farmers Union and FAO-supported post-harvest projects, are working with farmers to promote these simple practices in tandem with new storage tools.
Back in Hurungwe, Mai Chuma runs her hand over the cool side of a metal silo. Inside lies the bulk of her family’s harvest — sealed, dry, and quiet. The rats can’t reach it, and the weevils inside have long since suffocated. When she opens the outlet in October, the grain will pour out as clean and hard as the day it went in.
The work of producing maize doesn’t end at harvest. Yet, with the right mix of traditional knowledge and modern storage solutions, Zimbabwe’s farmers can keep the harvest they’ve already earned — strengthening household food security, supporting local markets, and moving a step closer to the zero-hunger future imagined in the UN Sustainable Development Goals.
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