Herbicidal mixtures comprising an auxin herbicide and an adjuvant comprising a salt having a quaternary ammonium cation and/or a phosphonium cation are described. The adjuvant reduces the volatility of the auxin herbicide and/or counteracts the negative impact on the volatility of the auxin herbicide caused by the addition of a co-herbicide. Methods of preparing the herbicidal mixtures are also described.METODO PARA PREPARAR MEZCLA HERBICIDA DE UN HERBICIDA DE AUXINA QUE COMPRENDE UN PRIMER CATION Y UN ADYUVANTE QUE COMPRENDE UNA SAL QUE COMPRENDE UN SEGUNDO CATION. MEZCLA HERBICIDA, COMPOSICIÓN ADYUVANTE, METODOS.