Enhanced method of killing weeds with glyphosate herbicide

8-24 2n7-23 1-4 2m2mA method is provided of enhancing the herbicidal activity of a glyphosate herbicide, comprising adding to the glyphosate herbicide a mixture of a first surfactant and a second surfactant at a weight ratio of total surfactant to glyphosate of about 1:30 to about 2:1, wherein the first surfactant has a chemical structure comprising a cationic or protonatable amino group and a Clinear or branched, saturated or unsaturated hydrocarbyl group, and the second surfactant has the formula R-CO-NR′-(CR′)-COOM where R is a Clinear or branched, saturated or unsaturated hydrocarbyl group, n is 1 to 4, M is hydrogen or a cationic counterion, and R′ groups are each independently hydrogen, Calkyl or a group -(CH)-COOM where m is 1 to 4 and M is as defined immediately above, with the proviso that no more than one R′ group is such a group -(CH)-COOM; the weight ratio of the first to the second surfactant being about 1:10 to about 10:1. Also provided is a herbicidal composition prepared according to the above method. The first and second surfactants exhibit a synergistic interaction in enhancing herbicidal activity of the glyphosate herbicide.