Dicarboximides of the formulae Ia, Ib and Ic ##STR1## where X is oxygen or sulfur,R.sup.1 is hydrogen, halogen, cyano, alkyl, cycloalkyl, alkenyl, alkynyl, alkoxy, alkenyloxy, alkynyloxy, alkylthio, haloalkoxy, haloalkylthio, alkylsulfonyl, haloalkylsulfonyl, phenyl, phenylalkyl, phenoxy or phenylthio, a 5-membered or 6-membered saturated or aromatic heterocyclic radical containing one or two hetero atoms selected from the group consisting of oxygen, sulfur and nitrogen, where the stated organic radicals may be further substituted, andR.sup.2 is hydrogen, hydroxyl, alkoxy, alkyl, cycloalkyl, alkenyl, alkynyl, di-C.sub.1 -C.sub.4 - alkylamino, a 5-membered or 6-membered heterocyclic saturated or aromatic radical having one or two hetero atoms selected from the group consisting of oxygen, sulfur and nitrogen, phenyl or naphthyl, where the stated organic radicals may be further substituted,and plant-tolerated salts of the dicarboximides I, except for 3-methylisoxazole-4,5-dicarboximide and thiazole-4,5-dicarboximides in which R.sup.2 is phenyl when R.sup.1 is methyl or 2-thiazolyl,and herbicides containing these compounds.