1. Choice of variety and selection of healthy seeds
Select the most suitable seeds for planting. Indigenous seeds have been developed for hundreds of generations and are well adapted to the areas where they are grown, whereas some modern varieties are higher yielding but may be more susceptible to pests. There is a widespread perception that modern, high-yielding varieties of maize may be more susceptible to storage pests. These varieties often have open cob husks, allowing insects and birds to easily attack maize in the field, whereas some of the traditional varieties have closed husks, thus effectively protecting the crop from insect attack. The same have been observed with some sorghum varieties. Therefore, the increased yield offered by some varieties should be weighed against the susceptibility to storage pests, the expected period of storage and the price to be expected for grain of a particular damage level. Efforts are going on to develop high yielding varieties with resistance to storage pests
Select the best seeds for next years planting avoiding damaged and sick looking seeds.
2. Choosing harvest time
If planting and harvesting is planned so that harvest falls in the dry season, there are no special problems with drying the crop. Care should be taken when cultivating new high yielding and early ripening varieties, since the harvest may fall in the wetter part of the year, and this may create problems of storage.
Some storage pests (e.g. bean beetles, cowpea bruchids, the larger grain borer and some moths) infest beans and grains in the field only when the crop is almost dry. Timely harvest can therefore ensure that these pests are not carried into the store along with the beans or grain. Thus, timely harvesting (avoiding late harvesting) significantly reduced infestation by the bean bruchid and cowpea bruchids in Kenya (Olubayo and Port, 1997). As a rule, do not leave crops in the field when they are ready for harvest, this increases the chances of infestation by some storage pests
Drying is an important procedure in storage protection. It prevents seed form germinating and prevents attack by fungi. Some fungi can cause cracking of seed thereby making the seeds more susceptible to pest attack. All seed must be dried to 12-13 % moisture in order to be stored safely. To make sure the seed is properly dried put one seed or kernel in the mouth and chew. If it cannot easily be cracked it is dry enough - if it crushes between the teeth it is not dry enough. This is known as the tooth test. See also salt test in 'The Organic Farmer Magazine' No. 30. November 2007.
Heat used for drying the produce will also kill larvae and chase away adults of insect storage pests. Care should be taken to avoid overheating since excessive heat can damage seed or grains. Care should be taken not to exceed the following temperatures: beans: 35 degC - seeds: 43 degC - cereals: 60 degC.
The following methods of drying are possible:
- Seed can be spread out in the sun on a hard clean surface to dry for several days in dry weather, until a seed cannot be bitten into when putting it in the mouth. The thickness of the layers of cobs, panicles, pods or grains must not exceed 5 cm, and the seed must be turned regularly in order to ensure good and even aeration. In the evening, the produce must be put in a pile and covered.
- Simple driers. Several designs of solar driers are available.
4. Sorting and cleaning the produce
Check whether the produce is infested by taking samples. Pay particular attention to cracks and gaps where insects may hide. If the produce is infested, ensure it is stored separately (quarantine) and treated in order to prevent the pests infesting clean produce. In case of heavy infestation discard the produce. In case the produce is slightly attacked, heating to no more than 50degC can kill moths and weevils; use a thermometer, as heating to any higher temperature will destroy the germination capacity the seeds See also heat treatment for seeds click here.
Removal of infested grains or cobs and pests can also be done by hand, sieving, winnowing or moving the grain (shaking, restacking). When using methods that merely separate the pests from the stored product, ensure that the pests removed from the produce are killed to avoid reinfestation.
5. Store location
Site stores away from any potential source of infestation. The grain and tuber moths are good flyers and adults from infested stores often infest growing crops in the field. Separations of stores from fields may help to reduce attack.
6. Characteristic of store
A good seed store must be airy, shady, cool and dry. Temperature variations should be as small as possible, because it encourages condensation of water, which promotes fungal development.
Crops in the store should be protected against dampness rising from the ground, and the site should be safe from flooding in the rainy season. The roof should have no leaks. Keep the temperature and humidity as low as possible (perform controlled ventilation). There are indications that storing grain in a dry place may help reduce infestation of grain moths.
Prevent pest entry by sealing the store (windows, doors, ventilation facilities) with insect-proof gauze. In Malawi, plastering stores with mud to reduce water uptake was found to be effective (Golob and Muwalo, 1984).
Hermetic, airtight storage at low humidity gives good protection against storage pests. However, to avoid mould growth care should be taken to ensure that the produce is dry. This is particularly applicable for long-term storage in warm dry areas. It is advisable however, not to store seed grain for more than a few months. In conditions where the relative humidity is high, airtight storage is not recommended due to the risk of mould growth.
Hermetic storage is useful for storing small amount of seeds or grains (e.g. to be used for replanting); they can be stored in a strong airtight container with a close fitting lid (glass, ceramic, strong plastic can be useful). Ceramic pots that do not have lids must be covered very carefully or topped up with dry soot, ashes or fine dry soil.
7. Storage hygiene
Always keep the store and its surroundings clean. It has been said: "the most important, economic and effective tool for storage hygiene is the broom". Before newly harvested crops are stored, the store should be carefully prepared well ahead of time. Old stored products should be removed and the room completely cleaned up. The whole building should be well aired and if possible fumigated or disinfected (see store fumigation and disinfection below). The walls roof and floor should be both watertight and rat proof, and small holes and cracks, which are potential breeding places for storage insects, should be sealed.
8. Inspecting the store
Periodic inspection (weekly to fortnightly) and removal of any infested produce is essential. Check for droppings and footprints of birds and rodents. Look for flying moths at dusk. Brush stacks of bags with a stick or broom to disturb and discover resting moths. Lift bags in order to detect moth cocoons along the line where bags touch each other.
When looking for beetles, pay particular attention to cracks, bag seams and ears where they often hide. Empty individual bags in a thin layer onto a sheet and examine the contents for beetles and larvae. This should be done in the shade so that the insects do not flee immediately.
Insects can be also be sieved out using a box sieve with a mesh of 1 to 2 mm. Identify the insect found in order to perform the correct treatment. These measures should prevent the breeding of carry-over insects from former crops. The surroundings should also be cleared to discourage easy re-infestation by insects and rodents.
Infection with fungi can be detected by the mouldy smell, which is noticeable even before any visual changes to the product can be seen. Pay attention to water marks on bags, which can be still noticed after the bags have dried.
9. Store fumigation
Farmers in the Philippines as well as in Benin lit fires in which powdered chilli pepper is burnt underneath grain stores once a month to keep away storage pests. One disadvantage is that the smoke is very sharp and uncomfortable for human eyes and respiratory system.
After the store has been cleaned completely and all old deposits of dust (possibly containing insect eggs) has been removed, it is good practice to dust the whole store with diatomite earth, lime or ashes as a further prevention of problems. Where larger grain borer has attacked the wood in the construction, the wood should be treated with any of the approved wood preservatives or thoroughly sprayed with kerosene, oil mixture to get rid of any surviving grain borers.
|Raised modernised granary with a high iron sheet roof with old oil smeared on the lower side of the support poles to prevent termite attack.
Ⓒ J. Maundu, icipe
|Raised traditional granary with several layers of thick grass and old oil smeared on the lower part of support poles to prevent termite attack.
Ⓒ J. Maundu, icipe