The present invention relates to novel effective alkynyl-substituted 3-phenylpyrrolidine-2,4-diones according to the general formula (I) or agrochemically acceptable salts thereof, where X═C1-C4-alkyl, C1-C4-haloalkyl or C3-C6-cycloalkyl; Y═C1-C4-alkyl or C3-C6-cycloalkyl, n=1, 2 or 3; m=1 or 2; R1═C1-C6-alkyl, or C3-C6-cycloalkyl, R2=hydrogen or methyl; R3═C1-C3-alkoxy-C1-C3-alkyl, or a saturated five- or six-membered heterocycle with an oxygen or sulphur atom; G=hydrogen, a cleavable group L or a cation E. The invention also relates to the use of the compounds according to the invention for controlling weeds and weed grasses in crops of useful plants.