The herbicides used in this study were obtained from a local agricultural dealer store in Ibadan. The herbicides used were: Atrylone 80WP, trademark of Insis Limited (atrazine); primextra, a product of Syngenta (a combination of atrazine and metolachlor); Glysate, Nantong Ji Angshan Agrochemicals (glyphosate); and Gramoxone, a product of Syngenta (paraquat).