Herbicidal picolinamide derivatives

A compound of the formula I ##STR22## in which Z represents an oxygen or sulphur atom,

• R.sup.1 and R.sup.2 each independently represents a hydrogen atom or an optionally substituted C.sub.1-10 alkyl, C.sub.2-10 alkenyl, C.sub.2-10 alkynyl, C.sub.3-8 cycloalkyl, (C.sub.3-8 cycloalkyl) C.sub.1-10 alkyl, C.sub.6-10 aryl, C.sub.6-10 arylC.sub.1-10 alkyl or C.sub.1-10 alkylC.sub.6-10 aryl group or one but not both of R.sup.1 and R.sup.2 may additionally represent a hydroxy group or an optionally substituted C.sub.1-10 alkoxy, C.sub.2-10 alkenyloxy, C.sub.2-10 alkynyloxy, C.sub.1-10 alkylcarbonyl, amino, mono- or di-C.sub.1-10 alkylamino, C.sub.1-10 alkoxycarbonylamino, C.sub.6-10 arylamino, C.sub.6-10 arylC.sub.1-10 alkylamino or diC.sub.1-10 alkylcarbamoyl group,
• R.sup.3 independently represents a halogen atom, a C.sub.1-10 alkyl, C.sub.1-10 alkoxy, C.sub.1-10 alkylthio, diC.sub.1-10 alkylamino or C.sub.1-10 haloalkyl group,
• R.sup.4 represents a hydrogen or halogen atom, an optionally substituted C.sub.1-10 alkyl, C.sub.2-10 alkenyl, C.sub.2-10 alkynyl, C.sub.3-8 cycloalkyl, (C.sub.3-8 cycloalkyl) C.sub.1-10 alkyl, C.sub.6-10 aryl, C.sub.6-10 arylC.sub.1-10 alkyl, C.sub.1-10 alkylC.sub.6-10 aryl, C.sub.1-10 alkoxy, diC.sub.1-10 alkylcarbamoyl, acyl or a cyano group,
• R.sup.5 and R.sup.6 each independently represents a hydrogen or halogen atom, an optionally substituted C.sub.1-10 alkyl, C.sub.2-10 alkenyl, C.sub.2-10 alkynyl, C.sub.3-8 cycloalkyl, (C.sub.3-8 cycloalkyl)C.sub.1-10 alkyl, C.sub.6-10 aryl, C.sub.6-10 arylC.sub.1-10 alkyl, C.sub.1-10 alkylC.sub.6-10 aryl, C.sub.1-10 alkoxy, amino, mono-or di-C.sub.1-10 alkylamino, C.sub.1-10 alkoxycarbonylamino, C.sub.6-10 arylamino, diC.sub.1-10 alkylcarbamoyl group, and
• n represents 0, 1, 2 or 3, and in which said optional substituents are selected from the group consisting of halogen atoms or nitro, cyano, C.sub.1-6 alkyl, C.sub.1-6 haloalkyl, C.sub.1-6 alkoxy, C.sub.1-6 haloalkoxy, formyl, C.sub.1-6 alkoxycarbonyl, carboxyl, phenyl or amino groups, said amino optionally substituted by one or two groups selected from C.sub.1-10 alkyl, C.sub.6-10 aryl, C.sub.3-8 cycloalkyl, (C.sub.3-8 cycloalkyl)C.sub.1-10 alkyl, C.sub.6-10 arylC.sub.1-10 alkyl, and C.sub.1-10 alkylC.sub.6-10 aryl.