Rice pests of shifting cultivation in Côte d\u27Ivoire, West Africa

Traditional shifting cultivatiOn appears to be sustainable if fallow periods are sufficient to restore soil fertility, maintain soil structure and suppress pests. These traditional systems are threatened in West Africa because of increasing land pressure resulting in shorter fallow periods. Studies were conducted on farmers\u27 fields in Côte d’lvoire to determine how fallow length affects populations of insect pests and their natural enemies and weed growth and yield losses due to weeds. Length of fallow influenced the abundance of certain arthropod species as indicated by sweep-net sampling. Populations of the stalk-eyed flies Diopsis spp., leaf·feeding beetles, and leafhoppers/spittlebugs were significantly higher in the long fallow (5-13 years) fields than in the short fallow (\u3c3 years) fields. The natural enemy complex consisting of spiders, predaceous ladybird beetles and dragonflies/damselflies also increased with length of fallow, while fallow period had no effect on the number of assassin bugs. Ants, spiders and ground beetles (Carabidae) were most abundant in pitfall traps. Spiders were the most abundant taxa in quadrat sampling on the soil surface. Chromolaena odorata was the principal weed species in rice fields. and it dominated much of the fallow vegetation. Weed growth was less on upland areas compared with hydromorphic areas, and weed growth was greater on fields cleared after short fallow than those cleared after long fallow. Grain yields were substantially greater on researcher than on farmer weeded plots