Buckwheat (Fagropyrum esculentum Moench.), cabbage (Brassica oleracea L), and conventional and glyphosate-resistant varieties of canola (Brassica napus L.) were used to study the bases of saflufenacil and glyphosate interactions. Compared to the addition of Merge (surfactant), the addition of both Transorb (i.e., commercial product, Transorb formulation with glyphosate) and Merge increased the cuticular absorption of [(14)C] saflufenacil in cabbage plants with thick epicuticular wax layers. However, in all cases, the addition of glyphosate reduced the translocation of [(14)C]saflufenacil in glyphosate-susceptible plants, while translocation was not affected in glyphosate-resistant canola. Moreover, the phytotoxicity of saflufenacil reduced the activity of glyphosate, possibly by reducing its translocation in all plant species studied. Increased absorption of saflufenacil by the addition of Transorb (i.e., Transorb formulation with glyphosate) plus Merge appears to increase its contact activity, thus the interaction of saflufenacil and glyphosate involves two separate processes, absorption and translocation.