Grain storage to protect against insects

If insects get into stored grain, a third of your harvest can be lost.

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The saw-toothed beetle, the grain weevil and the wonderfully named confused flour beetle are some of the many different insects that seek out stored grain. It’s important to know how and where to store grain, or you could lose up to a third of your harvest. Grain containing insects can become mouldy and poisonous to human beings. There are a number of ways to store grain.

Grain huts
Huts for storing wheat, sorghum, dry beans and mealies should not be built too close to grain crops to stop insects moving easily from one to the other.

Bags containing maize must be placed in a clean, cool grain hut. Mealies in bags can be hung in a tree – although certain flying insects can damage grain stored in this way.

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Clay pots
Clay pots (zefala) can be made from a mixture of ash and cattle manure. The odour of the manure and ash wards off insects. Keep the pots in an ordinary hut or under a roof.

This storage method was developed in the Cameroon. In an open spot make a circle with a radius of about 100cm and build a 60cm-deep foundation of stones and cement. Construct your storage container on top of this. Make a basket using chicken wire and apply cement-based plaster, inside and out. The thickness of the wall will depend on the size of the container – 4cm is recommended for a bin with a 1m³ capacity and 6cm for one with a 14m³ capacity. Finally, cover the opening and construct a thatched roof over the bin to provide shade and afford protection against rain.

Grass baskets
Grass baskets (izisulu) can be woven from bamboo splits and come in different sizes. They must be waterproofed to keep the grain dry. Smaller baskets can be stored in the kraal wall.

Grain wells
Wells (izisele) are dug in the kraal or against a steep incline, with an opening just big enough for a person to enter. The well can be plastered with cattle manure or lined with wattle. One well can store up to 10 bags of grain. The opening is covered with a stone and the sides of the cover are sealed tightly with clay. Caution is advised with this method as there can be a dangerous gas build-up from cattle manure. People entering wells have died after being overcome by poisonous gases.

The storage place must be clean. Insects breed easily and thrive among old maize kernels, old maize bags and dust. Storage facilities must be flushed out or scrubbed down before grain is stored. Insecticides can be used, but they’re expensive and poisonous. Contact your local co-op or extension officer for advice here.

Insects can be controlled naturally by doing one of the following before storing the grain:

  • Pick dry leaves from the lower part of the cat’s tail aloe (Aloe castanea), burn the leaves and mix the ashes with the grain.
  • Grind dry maize leaves and mix them with the grain.
  • Mix wood ash or fine, dry clay with the grain. 
  • In each of these instances, the ash/dry clay comes into contact with the insects when they crawl around in the grain.
  • In the process, the waxy layer covering the insects is rubbed off and they die of dehydration. Before the grain is used, the clay/ash can be removed by washing or sieving. 

Insects in flour or fine grain can be a real problem. For example, the larva of the tropical warehouse moth spins constantly while moving through the grain, covering the grain with threads. Ash cannot be used to control insects as it’s impossible to sieve it from flour or fine grain. Flour must therefore be stored in an airtight container in a cool, dry place.

Source: The department of agriculture and the ARC-Plant Protection Research Institute.
For further information about constructing a ferrumbu and other storage methods mentioned, contact the Plant Protection Research Institute on 012 319 7090/7087