The phyto-toxicological effects of a selective herbicide Atraforce® on onions (Allium cepa L) was assessed using the standard protocol of the Organization for Economic Co-operation and Development (OECD) # 208. The mean specific % growth rate relative to the control recorded was 77 ± 1.0, 70 ± 0.0, 60 ± 0.5, 47 ± 0.5 and 21 ± 0.44% with respect to the exposed concentrations (0.0625, 0.125, 0.25, 0.5 and 1.0 mg/L). The mean effective concentration (EC50) for Atraforce® using root growth was 0.323 ± 0.02 mg/L, with a safe limit estimated at 0.0323 ± 0.04 mg/L. The Ecotoxicological Risk Assessment Matrix (ERAM) was used to classify Atraforce® as D 4 (P; E; C), that is 16 (P; E; C), which was considered high risk to plants, the environment and community based on the frequency of application / exposure. The results from this appraisal suggested that the use of the herbicide Atraforce® could cause deleterious effects on these viable plant and vegetable species.