Losses in Stored Maize in Malawi (C. Africa) and Work Undertaken to Prevent them1

Abstract

AbstractResearch on maize storage in villages, conducted in Malawi (C. Africa) between 1968–1972 is described. Large differences in susceptibility to insects were found between the maize varieties which are currently grown. Local varieties were very resistant, improved varieties had a higher susceptibility while certain hybrids were very easily damaged by insects. Surveys showed that the annual loss was still small because most of the crop consists of local varieties.Lindane 0.5% dust applied at a dosage of 12 ppm on cobs with husks gave a good protection for about 10 months. This insecticide, however, cannot be used anymore because it may contaminate tobacco, the main export crop. Farmers therefore have to go over to the storage of shelled maize. Because of the occurrence of resistance to insecticides other techniques to prevent storage losses are necessary. Recommended is the breeding of high yielding varieties with a good husk cover and hard grains, the use of inert dusts and the development of small silos which can be fumigated.SummaryBetween 1968–1972, a study was made on losses of maize stored in villages in Malawi and different methods were tested to reduce these losses. Cylindrical cribs made from bamboos or twigs are used to store the maize on the cob with the husks. Moisture content of the maize at harvest in June‐July is around 14–15 %. During the subsequent dry season, it dries to about 11 % in November, after which the moisture content increases again to about 14 % in the rainy season.Infestation by pests such as Sitophilus spp. and Sitotroga cerealella starts in the field. Populations build up slowly during the dry season but in the rainy season those of Sitophilus increase rapidly while those of Sitotroga decrease. The percentage of bored grains shows the same trend, a slow increase during the dry season, followed by a steep rise after the onset of the rains. There were, however, considerable differences in susceptibility to insects between the maize varieties grown in Malawi. Local varieties characterized by hard grains and a good husk cover were very resistant to insect damage. Grain damage at the end of a storage period of 9 months was, in local varieties, about 10%; improved varieties showed after the same period a grain damage of 15–30%, while for certain varieties like SR 52, which have very soft grains and a poor husk cover 70–90% of the grains were bored.Several techniques were tested to assess losses in the country which all, however, had their limitations and were in some way or another unsatisfactory. The most reliable method consisted of sampling 25 cobs from the top layer of the crib. These were shelled and thoroughly mixed and then a sub‐sample of about 700 g was taken which was immediately fumigated. In the laboratory the percentage of bored grains was determined in a sub‐sample of 1,000 grains. The overall loss of the 1971 crop caused by insects was very low (about 1%) because over 90% of the crop consisted of local varieties. A survey conducted in a small area showed that the combined loss due to rodents, termites and moulds was about 1–3%.Lindane 0.5 % dust was tested as a protectant of maize cobs. It was found to be most effective when applied on cobs with husks. Treated cobs without husks became infested by S. cerealella. Lindane dust was made available to the farmers but had to be withdrawn because of possible incidences on the tobacco trade. Farmers are now advised to shell their maize during the dry season and to mix it with malathion dust at 1 %. Resistance to insecticides will, however, create problems in the near future. It is recommended, therefore, to develop high yielding maize varieties which are more resistant to storage pests, to look into the possibilities of using inert dusts as pesticides and to develop cheap small silos which are insect proof and can be fumigated.