Herbicidal 2, 6-disubstituted pyridines and 2, 4-disubstituted pyrimidines

A compound of the general formula I ##STR31## wherein A represents a substituted aryl group or an optionally substituted pyridyl or pyrazolyl group or a difluorobenzodioxolyl group;

• m represents an integer from 0 to 5;
• n represents an integer from 0 to 2;
• R.sup.1 (or each R.sup.1) independently represents a hydrogen atom, a halogen atom, an optionally substituted alkyl, alkenyl, alkynyl, alkoxy, alkoxyalkoxy, alkoxyalkyl, dialkoxyalkyl, alkylthio, amino, alkylamino, dialkylamino, alkoxyamino or formamidino group;
• R.sup.2 (or each R.sup.2) independently represents a hydrogen atom, a halogen atom, an optionally substituted alkyl, alkenyl, alkynyl, alkoxy, alkoxyalkyl, alkoxyalkoxy, alkylthio, alkylsulphinyl, alkylsulphonyl group or a nitro, cyano, haloalkyl, haloalkoxy, haloalkylthio or SF.sub.5 group,
• X represents any oxygen or sulphur, atom;
• and
• Z represents a nitrogen atom.