Field trials were conducted to determine effects of cultivar and insecticide application on grain yield and yield loss of cowpea to insect pest during the 2008 and 2009 cropping seasons at Baga (13° 29ʺ N and 13° 32ʺ E), Lake Chad shore area of Nigeria. Three cowpea varieties (Kanannado, Borno brown and IT98k-1312), two insecticides [cypermethrin (30 g) + dimethoate (250 g) and neem seed aqueous extract] and three spray regimes (one each at budding, flowering and podding) were evaluated for the control of pest on cowpea. The treatments were laid in a strip-split plot design and replicated three times each. The results reveal that flower thrips (Megalurothrips sjostedti), Legume pod borer (Maruca vitrata), Blister beetle (Mylabris spp.) and Pod Sucking Bug (Anoplocnemi scurvipes) were the major insect pests of rainfed cowpea in the area. The variety Borno brown failed to produce flower in both seasons. IT98k-131-2 was more tolerant to damage by insect pests of budding, flowering and podding stages. Higher percentage increase in grain yield was achieved by three sprays of either Cymbush super EC (87.68 and 61.09%) or NSAE (81.85 and 53.69%) over control in 2008 and 2009, respectively. Pod damage of 22.3-26.3% was recorded in untreated control while in cowpea treated with Cymbush super EC and NSAE, pod damage was 7.0-7.4 and 8.8-10.6%, respectively. Grain yield loss of about 43-45% was recorded in untreated control and this was attributed to the damage caused by insect pests of budding, flowering and podding stages. Cowpea treated with Cymbush super EC and NSAE had 16-31 and 31-34% grain loss, respectively. IT98k-131-2 sprayed three times with either Cymbush super EC or NSAE gave consistently the best grain yield in both seasons. However, NSAE gave averagely higher marginal return (25.45) than Cymbush super EC (18.00) in the study. Three sprays also gave the highest marginal returns over control. Insecticide application once each at budding (35-40 DAS), flowering (50%) and podding (10 day after second spray) was effective in reducing insect pests’ infestation and increased grain yield of rainfed cowpea in the Lake Chad shore area. Three sprays of either Cymbush super EC or NSAE gave economically the best control of insect pest and the best grain yield of cowpea. The variety IT98k-131-2 can be cultivated for resistance and high yield. Neem seed aqueous extract can be used as an alternative insecticide for safe, cheap and effective control of insect pests in cowpea.
Key words: Cowpea variety, spray regime, NSAE, insect pest, cymbush super EC, Lake Chad shore.