Use of one or more compounds of the formula and/or their salts in which R 1 represents hydrogen, -C(=O)-O-R C or -C(=O)-R C, where the group R C is in each case selected from the group consisting of: (i) unsubstituted (C 1 -C 6)-alkyl, unsubstituted (C 2 -C 6)-alkenyl, unsubstituted (C 2 -C 6)-alkynyl, substituted (C 1 -C 6)-alkyl, substituted (C 2 -C 6)-alkenyl and substituted (C 2 -C 6)-alkynyl, where each of these substituted radicals is substituted by one or more radicals from the group consisting of methyl, hydroxyl, fluorine and chlorine, (ii) (C 3 -C 6)-cycloalkyl, (C 3 -C 6)-cycloalkyloxy-(C 1 -C 4)-alkyl, phenyl, where each of these radicals is unsubstituted in the cyclic moiety or substituted by one or more identical or different radicals R B, where R B is independently of any other radicals R B present selected from the group consisting of halogen (here preferably fluorine, chlorine, bromine), cyano, nitro and (C 1 -C 4)-alkyl (here in turn preferably methyl), where R C preferably comprises a total of 1 to 12 carbon atoms, with preference a total of 1 to 10 carbon atoms, (R 2) n represents n substituents R 2, where, in the case that n = 1, the substituent R 2 or, in the case that n is greater than 1, each of the substituents R 2 independently of the others represents fluorine, chlorine, bromine, iodine, cyano, nitro, methyl, ethyl, methoxy, methylthio, methylsulphinyl, methylsulphonyl, trifluoromethyl, trifluoromethoxy, trifluoroalkylthio, trifluoromethylsulphinyl or trifluoromethylsulphonyl, and (R 3) m represents m substituents R 3, where, in the case that m = 1, the substituent R 3 or, in the case that m is greater than 1, each of the substituents R 3 independently of the others represents fluorine, chlorine, bromine, iodine, cyano, nitro, methyl, methoxy, methylthio, methylsulphinyl, methylsulphonyl, trifluoromethyl, trifluoromethoxy, trifluoroalkylthio, trifluoromethylsulphinyl or trifluoromethylsulphonyl, and m represents 0, 1, 2, 3, 4 or 5, preferably 0, 1, 2, 3 or 4, in particular 0, 1, 2 or 3, and n represents 0, 1, 2, 3, 4 or 5, preferably 0, 1, 2 or 3, in particular 0, 1 or 2, as herbicides and/or plant growth regulators, preferably in crops of useful plants and/or ornamental plants. R 1 represents hydrogen, -C(=O)-O-R C or -C(=O)-R C, where the group R C is in each case selected from the group consisting of: (i) unsubstituted (C 1 -C 6)-alkyl, unsubstituted (C 2 -C 6)-alkenyl, unsubstituted (C 2 -C 6)-alkynyl, substituted (C 1 -C 6)-alkyl, substituted (C 2 -C 6)-alkenyl and substituted (C 2 -C 6)-alkynyl, where each of these substituted radicals is substituted by one or more radicals from the group consisting of methyl, hydroxyl, fluorine and chlorine, (ii) (C 3 -C 6)-cycloalkyl, (C 3 -C 6)-cycloalkyloxy-(C 1 -C 4)-alkyl, phenyl, where each of these radicals is unsubstituted in the cyclic moiety or substituted by one or more identical or different radicals R B, where R B is independently of any other radicals R B present selected from the group consisting of halogen (here preferably fluorine, chlorine, bromine), cyano, nitro and (C 1 -C 4)-alkyl (here in turn preferably methyl), where R C preferably comprises a total of 1 to 12 carbon atoms, with preference a total of 1 to 10 carbon atoms, (i) unsubstituted (C 1 -C 6)-alkyl, unsubstituted (C 2 -C 6)-alkenyl, unsubstituted (C 2 -C 6)-alkynyl, substituted (C 1 -C 6)-alkyl, substituted (C 2 -C 6)-alkenyl and substituted (C 2 -C 6)-alkynyl, where each of these substituted radicals is substituted by one or more radicals from the group consisting of methyl, hydroxyl, fluorine and chlorine, (ii) (C 3 -C 6)-cycloalkyl, (C 3 -C 6)-cycloalkyloxy-(C 1 -C 4)-alkyl, phenyl, where each of these radicals is unsubstituted in the cyclic moiety or substituted by one or more identical or different radicals R B, where R B is independently of any other radicals R B present selected from the group consisting of halogen (here preferably fluorine, chlorine, bromine), cyano, nitro and (C 1 -C 4)-alkyl (here in turn preferably methyl), (R 2) n represents n substituents R 2, where, in the case that n = 1, the substituent R 2 or, in the case that n is greater than 1, each of the substituents R 2 independently of the others represents fluorine, chlorine, bromine, iodine, cyano, nitro, methyl, ethyl, methoxy, methylthio, methylsulphinyl, methylsulphonyl, trifluoromethyl, trifluoromethoxy, trifluoroalkylthio, trifluoromethylsulphinyl or trifluoromethylsulphonyl, and (R 3) m represents m substituents R 3, where, in the case that m = 1, the substituent R 3 or, in the case that m is greater than 1, each of the substituents R 3 independently of the others represents fluorine, chlorine, bromine, iodine, cyano, nitro, methyl, methoxy, methylthio, methylsulphinyl, methylsulphonyl, trifluoromethyl, trifluoromethoxy, trifluoroalkylthio, trifluoromethylsulphinyl or trifluoromethylsulphonyl, and m represents 0, 1, 2, 3, 4 or 5, preferably 0, 1, 2, 3 or 4, in particular 0, 1, 2 or 3, and n represents 0, 1, 2, 3, 4 or 5, preferably 0, 1, 2 or 3, in particular 0, 1 or 2, as herbicides and/or plant growth regulators, preferably in crops of useful plants and/or ornamental plants.