A herbicidal agent comprising: (1) water; (2) ioxynil and/or a derivative thereof; (3) a compound of the formula (I) RO—(CH2H4O)n(CH3H6O)m—R′  (I) wherein RO is an alcohol radical selected from the group consisting of branched or linear, saturated or unsaturated monohydric alcohols having from 1 to 6 carbon atoms, or a polyol radical having from 2 to 12 carbon atoms and from 2 to 6 hydroxyl groups; R′ is hydrogen or an ester group —CO—R″ wherein R″ is a branched or linear, saturated or unsaturated alkyl radical having 5 to 29 carbon atoms, n is a number between 1 and 50 and m is zero or a number between 1 and 10. The herbicidal agents permit high penetration of the herbicide into the plant.