Compounds of the formula
where Q is an optionally substituted quinazoline ring system, W is oxygen or sulphur, R is one of a range of aliphatic or aromatic hydrocarbon substituents and A is a monocyclic or bicyclic ring system wherein that ring by which A is attached to the remainder of the molecule is a five- or six-membered ring with at least two ring nitrogens. The compounds are effective herbicides.