Field evaluation of neem seed extract for the control of major pests of cowpea in northern Ghana

Abstract

Field studies were conducted at the Experimental Farm of the Savanna Agricultural Research Institute (SARI), Nyankpala, northern Ghana, during the 2006 cropping season to evaluate the effect of aqueous neem (Azadirachta indica A. Juss) seed extract at 5, 10, 15 and 20 per cent on Aphis craccivora Koch., Megalurothrips sjostedti Tryb., Maruca vitrata Fab., and a complex of pod and seed-sucking bugs of cowpea (Vigna unguiculata L. Walpers), as well as their effect on the grain and fodder yields of the crop. The results showed that the incidence and abundance of all the target insect pests were significantly affected by the neem extract treatments. Cowpea grain yield was significantly higher in all the neem-treated plots than in the control. The 15 per cent neem seed extract treatment proved as effective as that of the 20 per cent in increasing the grain yield of the cowpea crop. However, none of the neem treatments was as effective as the synthetic insecticide (Karate) in cowpea grain yield. However, grain quality for the 15 and 20 per cent treatments was similar to that for the Karate treatment. Cowpea fodder yield was found to decrease with increasing concentration of the neem extract. Benefit-cost analysis for the grain and fodder yields showed that the 15 and 5 per cent neem extract treatments, respectively, had the best benefit-cost ratios. Therefore, the 15 per cent neem seed extract is recommended for use in controlling the major field insect pests of cowpea for maximum grain yield in the Guinea savanna agroecological zone of Ghana. However, for situations in which the grower is strapped for cash or neem seeds are inadequate, the 5 or 10 per cent extract may be used. The 5 per cent neem seed extract is recommended for dual-purpose cowpea cultivars for maximum returns on grain and fodder yield.