Efficacy of selected herbicides on weed control, cowpea (Vigna Uniguiculata L. Walp) performance and economic returns in Akamkpa, southeastern Nigeria

A two year (2007 and 2008) field trial was conducted in Akamkpa Local Government Area of Cross River State, Nigeria to evaluate the effects of selected herbicides on weed control, cowpea (Vigna uniguiculata (L.) Walp) performance and economic returns to management. A randomized complete block design with a split plot arrangement was used and replicated three times. The main treatments were three cowpea varieties: Sampea 7(IAR-48), Sampea 4(IAR-176) and IT.4532-1, while the sub treatments were five herbicides: atrazine, diuron, galex, glyphosate, primextra, and all applied pre – emergence (a day after sowing) at 2.0kg.ai/ha and control ((manually weeded and no herbicide application). Results showed that cowpea establishment did not differ significantly among cowpea varieties whereas herbicide type significantly (P IT.4532-1(2.55 tha-1) > Sampea 4 (2.28 tha-1). In contrast, grain yield differed significantly (P<0.05) among herbicide types irrespective of the cowpea varieties though no clear trend was exhibited. Averaged across both years indicated that Galex (3.42 tha-1) promoted grain production in Sampea 7 variety plot followed by Glyphosate (3.13 tha-1) and control (2.56 tha-1).In IT.4532-1 plot, glyphosate recorded the highest grain yield (3.20 tha-1) followed by Galex (3.11 tha-1) and the control (2.35 tha-1). The interaction effects between the cowpea varieties and the herbicide types on grain yield was significant (P<0.05) with Glyphosate, Galex and control highly favoured. The highest economic return (N 999,051.80) to management was obtained from Sampea 7(IAR-48) and was followed by IT.4532-1. This implies that Galex would be more effective in controlling weeds in cowpea plot followed by glyphosate particularly if Sampea 7(IAR-48) and IT.4532-1 varieties are planted. Keywords: Herbicides, weed control, cowpea performance, economic returns, Nigeria