Effect of sorghum and cowpea intercropping pattern on the spotted stemborer, Chilo partellus (Swinhoe) larval establishment in southwestern Kenya

Abstract

—An investigation was carried out on the effects of three patterns of sorghum (Sorghum bicolor) and cowpea (Vigna unguiculata) intercrops on larval establishment of the spotted stemborer, Chilo partellus, on sorghum at different growth stages. The intercrop patterns were: sorghum sown simultaneously with cowpea, sorghum sown 2 weeks before cowpea and sorghum sown 2 weeks after cowpea. Sole sorghum and sole cowpea were controls. Sorghum plants were infested at 4, 6 and 8 weeks after emergence (WAE). Ten days after infestation, the infested plants and their immediate neighbours in the same row were uprooted and dissected. The number of larvae recovered and their stages of development were recorded. Some predatory arthropods were monitored by direct egg counts and use of pitfall traps. Grain yields were recorded at harvest to determine land productivity. Larval establishment was significantly (P < 0.05) higher on sorghum plants in sole crop than in intercrops; it was also higher on sorghum plants infested 6 WAE than on other dates. More C. partellus larvae were lost from sorghum sown after cowpea than in other cropping patterns, and more larvae were lost from sorghum plants infested at 4 WAE than on other dates. More predatory arthropods were observed in cowpea cover compared to those found in sole sorghum—the arthropods may be responsible for the observed loss in C. partellus larvae in the intercrop. Land productivity was higher in sorghum sown simultaneously with or after cowpea than in other cropping patterns. Thus, intercropping increased larval loss in C. partellus and improved productivity.