Pyrazole derivatives, for use as herbicides, have the formula (I):
wherein
R 1 represents hydrogen, halogen or methyl; R 2 represents hydrogen, halogen, nitro, methyl, cyano, carboxy, (C 1 to C 8 )-alkoxy or (C 1 to C 4 )-alkoxycarbonyl; R 3 represents hydroxy, amino, (C 3 or C 4 )-alkenyloxy, (C 3 or C 4 )-alkynyloxy, (C 1 to C4)-alkoxy-(C 1 to C 4 )-alkoxy, (C 1 to C 4 )-alkylthio, (C 3 or C 4 )-alkenylamino, (C 1 to C 4 )-alkylsulfonylamino, (C 1 or C 2 )-alkoxy-(C 1 or C 2 )-alkylamino, -O-N=C-(CH 3 ) 2 , anilino, benzylamino, morpholino, (C 1 to C 6 )-alkoxy unsubstituted or substituted by (C 1 to C 4 )-alkoxycarbonyl, (C 1 to C 4 )-mono- or di-alkylamino group in which the or each alkyl group is unsubstituted or substituted by hydroxy or carboxy, or -OM wherein M represents an alkali metal, alkaline earth metal, ammonium or (C 1 to C 4 )-alkylammonium; R 4 represents halogen, methyl, (C 1 to C 4 )-alkoxy, -S(O) m -R 5 wherein m is 0, 1 or 2 and R 5 represents (C 1 to C 4 )-alkyl; X represents hydrogen, halogen, (C 1 to C 4 )-alkyl, (C 1 to C 4 )-alkylthio or (Ci to C 4 )-alkylsulfonyl; and Y represents (C 1 to C 4 )-alkyl or X and Y taken together with the atoms to which they are attached form a cyclopentyl or cyclohexyl ring unsubstituted or substituted with one or more methyl group.