Pyrimidinyl and triazinyl herbicides

A pyrimidine derivative of the formula:

• ##STR7## and salts thereof, where:
• Y is an alkyl group of 1 to 6 carbon atoms which is unsubstituted or is substituted by one or more halogen atoms, by cyano, by alkoxy of 1 to 4 carbon atoms, or by a group --COZ in which Z is a group --NR'R" to --OR' and R' and R" each represent hydrogen, alkyl of 1 to 6 carbon atoms, or phenyl;
• or is an amino group;
• R.sup.1 is substituted or unsubstituted alkyl group of 1 to 6 carbon atoms as defined above for Y;
• cycloalkyl group of 3 to 7 carbon atoms;
• phenyl which is unsubstituted or substituted by one ore more halogen atoms, nitro groups, amino groups, alkylamino, dialkylamino or acylamino groups where the alkyl moieties have from 1 to 4 carbon atoms, cyano groups, alkyl or alkoxy groups of 1 to 4 carbon atoms, alkoxycarbonyl groups in which the alkyl moiety is of 1 to 4 atoms, or phenoxy groups;
• or a hete ocyclyl group selected from furyl, pyridyl and thienyl which is unsubstituted or substituted by one or more alkyl groups of 1 to 4 carbon atoms;
• R.sup.2 is hydrogen, halogen, or alkyl of 1 to 6 carbon atoms;
• and
• R.sup.4 and R.sup.5, which may be the same or different, are each hydrogen, alkyl of 1 to 6 carbon atoms, alkoxy of 1 to 6 carbon atoms, amino, alkylamino of 1 to 6 carbon atoms, dialkylamino in which each alkyl moiety is of 1 to 6 carbon atoms, or halogen.