A use of a graft copolymer obtained by free-radical polymerization of a monomer mixture comprising N-vinyllactam, vinyl ester, and a polyether for increasing the activity of a pesticide is disclosed. A composition comprising a pesticide and a graft copolymer obtained by free-radical polymerization of a monomer mixture comprising i) 30 to 80% by weight of N-vinylpyrrolidone, N-vinylcaprolactam or mixtures thereof, ii) 10 to 50% by weight of vinyl acetate, and iii) 10 to 50% by weight of a polyether is also disclosed. Furthermore a method for preparing said composition by mixing the pesticide and the graft copolymer and a method for controlling phytopathogenic fungi and/or undesired plant growth and/or undesired attack by insects or mites and/or for regulating the growth of plants are also disclosed.
