Substituted pyridines of the formula ##STR1## in which A represents nitrogen or a C-X group where X represents hydrogen or halogen,Q represents oxygen or sulphur,R.sup.1 and R.sup.2 are identical or different and represent hydrogen, halogen, alkyl, halogenoalkyl, alkoxyalkyl, alkoxy, halogenoalkoxy, alkylthio, alkylamino or dialkylamino,R.sup.3 represents hydrogen, amino, nitro, hydroxyl, halogen, alkyl, halogenoalkyl, alkoxy, halogenoalkoxy, alkylamino, dialkylamino, alkylcarbonylamino, alkoxycarbonylamino or alkysulphonylamino,R.sup.4 represents hydrogen or alkyl andZ represents oxygen or one of the groups below: ##STR2## where R.sup.5, R.sup.6 and R.sup.7 are defined herein and their use in herbicide compositions.