The present invention relates to an adjuvant for enhancing the activity of pesticides comprising a polar solvent and a phosphate ester of the formula (A) (as described hereinbelow), it being possible for the phosphate ester of the formula (A) to be present as the free acid and/or as a salt, and where the polar solvent is miscible with water in any ratio and has a flash point of above 60° C. The invention furthermore relates to an agrochemical composition comprising a pesticide and the adjuvant to a process for the preparation of the adjuvant, wherein the polar solvent and the phosphate ester of the formula (A) are brought into contact to use of the adjuvant for enhancing the activity of a pesticide and to a method of controlling phytopathogenic fungi and/or undesirable vegetation and/or undesired insect or mite attack and/or for regulating the growth of plants, wherein the composition is allowed to act on the respective pests, their environment or the crop plants to be protected from the respective pests, on the soil and/or on undesired plants and/or on the crop plants and/or on their environment.
