Compounds of the general formula ##STR1## in which R.sup.1 and R.sup.2 each independently represents an alkyl group, Z represents a nitrogen atom or a group CH unsubstituted or substituted by a substituent X, m is 0 or an integer from 1 to 4, the or each Y represents a halogen atom, n is 0 or an integer from 1 to 5, and the or each X represents a halogen atom or a group selected from alkyl, haloalkyl, cyanoalkyl, alkenyl, alkynyl, alkoxy, alkenyloxy, alkynyloxy, alkylthio, alkenylthio, alkynylthio, cyano, nitro, alkylsulphonyl, alkylsulphinyl, and sulphonamido, have been found to have herbicidal activity.