Two field experiments were conducted at Ngala in the Lake Chad Basin during the wet seasons of 1981 and 1982 to investigate weed competition as well as chemical and manual weed control in irrigated cotton (Gossypium hirsutumL.) var. Acala 1517C. Pre‐emergence herbicides and their mixtures were tested in replicated, randomized block trials in which the cotton variety was grown 30 cm apart on 90 cm ridges and fertilized with 50 kg N/ha and 40 kg P2O5/ha. The results showed the importance of early weed competition in irrigated cotton. Weed control 14 days after cotton emergence produced optimum growth and yield. Subsequent weeding delay in 7‐day increments restricted crop growth and reduced yield significantly. Unweeded cotton suffered an average yield loss of 82.0%. Yields of plots treated with fluridone at 1.0 kg a.i./ha and fluometuron at 3.0 kg a.i./ha respectively applied 1 to 2 days after sowing were significantly higher than the yield of the untreated plots and plots hand weeded once later than 21 days after crop emergence. Plots hand weeded once however, yielded significantly higher than the untreated plots.