Effects of time of intercropping with maize on cowpea susceptibility to three major pests.

The value of intercropping cowpea (Vigna unguiculata (L.) Walp.) with maize (Zea mays L.) as a means of controlling three major cowpea pests was investigated by varying the time of planting of the cowpea intercrop. Simultaneous planting of maize and cowpea tended to increase infestation of cowpea by Maruca testulalis Geyer but not by Cydia ptychora Meyr. and thrips (mainly Megalurothrips sjostedti Trybom.). Subsequent interplanting of cowpea in maize, however, showed marked increase in the incidence of thrips (P = 0.01) and Cydia (P = 0.01) in the intercrops. Control of these pests by insecticide was not enhanced by intercropping. The extent of insect damage in the intercrops was determined by the interaction between time of sowing and cropping method. Planting cowpea at 12 weeks after the establishment of maize significantly reduced insect damage and therefore appears to be the best time to intercrop to achieve some measure of control of these pests. These findings are relevant to the development of a pest management scheme for cowpea involving the ecological concept.