Herbicidal tetrahydro(thio)pyran-2,4-dione derivatives

The invention relates to tetrahydro(thio)pyran-2,4-diones of the formula in which R represents hydrogen, a cation, alkylcarbonyl, C2-C10-alkenylcarbonyl or benzoyl which is optionally substituted by alkyl, R represents alkyl, R represents a non-aromatic heterocycle which has 5 to 7 ring members and not more than one double bond in the heterocyclic ring and which is optionally substituted by alkyl, X represents oxygen or sulphur, Z represents oxygen or the radical NO-R , where R represents alkyl, alkenyl, alkynyl, haloalkyl, haloalkenyl, alkoxyalkyl or the radical CH2-R in which R represents a 5-membered heterocycle having up to 3 hetero atoms, and, if appropriate, not more than 2 double bonds and up to 2 substituents selected from the group comprising alkyl, alkoxy, halogen, trifluoromethyl, alkoxymethyl, alkylthiomethyl and vinyl, or represents phenyl which is optionally substituted by up to 3 substituents selected from the group comprising alkyl, alkoxy, halogen, trifluoromethyl, nitro and dialkylamino, to processes for their preparation and to their use for controlling undesired plant growth for regulating the growth of plants.