Pyridine derivatives of the formulae ##STR1## where W, X, Y and Z are each C--R.sup.4, N or N.fwdarw.O, with the proviso that the ring contains only one heteroatom, and the substituents R.sup.1, R.sup.2 and R.sup.3 have the following meanings:R.sup.1 is alkoxy, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted alkenyl, or substituted or unsubstituted alkynyl,R.sup.2 is hydrogen,R.sup.3 is formyl, 4,5-dihydrooxazol-2-yl or --CO--A--R.sup.5 or --CO--NR.sup.6 R.sup.7,whereR.sup.4 is halogen, nitro, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted benzyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, alkoxy, alkylthio, haloalkoxy, haloalkylthio, alkenyloxy, alkynyloxy, alkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, substituted or unsubstituted phenoxy or phenylthio, a substituted or unsubstituted 5- or 6-membered heterocyclic radical having one or two heteroatoms selected from the group consisting of oxygen, sulfur and nitrogen, or is substituted or unsubstituted phenylA is oxygen or sulfur,R.sup.5 is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted benzyl, cycloalkyl, substituted or unsubstituted phenyl,one equivalent of a cation or the radical --N.dbd.CR.sup.8 R.sup.9 andR.sup.6 and R.sup.7 are hydrogen or alkyl or together denote a methylene chain having 4 or 5 members,their agriculturally utilizable salts, and their use for controlling unwanted plant growth.