Compounds (A) can be used for increasing the yield of useful plants or crop plants with respect to their harvested plant organs, wherein the Compound (A) is selected from compounds of the formula (I) or salts thereof, in which (R1)n is n radicals R1 where the R1 are identical or different and are each halogen or (C1-C4)-haloalkyl, n is an integer from 1 to 3, R2 is hydrogen, (C1-C6)-alkyl, (C1-C4)-alkoxy-(C1-C4)-alkyl, (C3-C6)-cycloalkyl, tri-(C1-C4)-alkyl-silyl or tri-(C1-C4)-alkyl-silylmethyl, R3 is hydrogen, (C1-C6)-alkyl, (C1-C6)-haloalkyl, (C2-C6)-alkenyl, (C2-C6)-alkynyl or (C3-C6)-cycloalkyl, and R4 is hydrogen or (C1-C12)-alkyl, preferably mefenpyr-diethyl (Compound (A1)]Selon l'invention, des composés (A) peuvent être utilisés pour augmenter le rendement de végétaux ou de cultures utiles, en ce qui concerne les organes récoltés, le composé (A) étant choisi parmi les composés de formule (I) ou leurs sels, (R1)n signifiant n radicaux R1, les radicaux R1 étant identiques ou différents et étant chacun halogène ou (C1-C4)-haloalkyle, n étant un nombre entier compris entre 1 et 3, R2 étant hydrogène, (C1-C6)-alkyle, (C1-C4)-alcoxy-(C1-C4)-alkyle, (C3-C6)-cycloalkyle, tri-(C1- C4)-alkyl-silyl or tri-(C1-C4)-alkyl-silylméthyle, R3 étant hydrogène, (C1-C6)-alkyle, (C1-C6)-haloalkyle, (C2-C6)-alcényle, (C2-C6)-alcynyle ou (C3-C6)-cycloalkyle, et R4 étant hydrogène ou (C1-C12)-alkyle, de préférence mefepyr-diéthyl (composé (A1).
