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, andR4 is hydrogen or (C1-C12)-alkyl,preferably mefepyr-diethyl (Compound (A1)]
