Abstract: A nicotinic acid derivative represented by general formula (I) or (II), a salt thereof, and a herbicide containing the same as the active ingredient, wherein A represents substituted phenyl, or 5- or 6- membered heterocycle, e.g., thienyl or pyridyl; R represents hydroxy, optionally substituted alkoxy or optionally substituted benzyloxy; R.sup.1 and R.sup.2 represent each independently alkoxy or halogen; R.sup.3 and R.sup.4 represent each independently hydrogen, hydroxy, cyano or alkoxycarbonyl, or they may be combined together to represent oxygen; X represents halogen, alkyl or alkoxy; n represents 0, 1 or 2; and Z represents methine or nitrogen. The compound and salts thereof can control annual or perennial weed growing on the land where various crops such as rice plant, wheat, cotton and corn grow for a wide period ranging from the pre-emergence to growth in a remarkably small dose.

Abstract: A condensed heterocyclic derivative of the formula ##STR1## (wherein R is a hydroxyl group, R.sup.3 or R.sup.4 is an alkoxy group, W is an oxygen atom, Yn is a hydrogen atom, Z is a methine group, and A is a 5- or 6-membered heterocyclic ring which may be substituted, and a herbicide, are presented. When used for paddy field treatment, upland soil treatment and foliage treatment, the condensed heterocyclic derivative of the present invention exhibits excellent herbicidal activities against gramineous and non-gramineous weeds without adversely affecting crop plants.

Abstract: A condensed heterocyclic derivative of the formula (I): ##STR1## (wherein R is a hydroxyl group, R.sup.3 or R.sup.4 is an alkoxy group, W is an oxygen atom, Yn is a hydrogen atom, Z is a methine group, and A is a 5- or 6-membered heterocyclic ring which may be substituted, and a herbicide, are presented. When used for paddy field treatment, upland soil treatment and foliage treatment, the condensed heterocyclic derivative of the present invention exhibits excellent herbicidal activities against gramineous and non-gramineous weeds without adversely affecting crop plants.