4-Phenylpyridazinone compounds (I) and their salts are new. 4-Phenylpyridazinone compounds of formula (I) and their salts are new. A : H, 3-6C-cycloalkyl or 1-6C-alkyl (substituted by n residues of halo, 3-6C-cycloalkyl, phenyl or halophenyl); B1 : 3-6C-cycloalkyl or 1-6C-alkyl (substituted by m residues of halo, 3-6C-cycloalkyl, phenyl or halophenyl); m, n : 0-3, with the proviso that m and n are not simultaneously 0; G : H, C(=O)R1, C(=L)MR2, SO 2R3, P(=L)R4R5, C(=L)NR6R7, E or R8; E : metal ion equivalent or ammonium ion; L, M : O or S; R1 : 1-6C-alkyl, 2-6C-alkenyl, 1-4C-alkoxy-1-6C-alkyl, di-1-4C-alkoxy-1-6C-alkyl or 1-4C-alkylthio-1-6C-alkyl (all substituted by n halo), 3-6C-cycloalkyl, phenyl, phenyl-1-4C-alkyl, heteroaryl, phenoxy-1-4C-alkyl or heteroaryloxy-1-4C-alkyl (all substituted by n residues of halo, 1-4C-alkyl or 1-4C-alkoxy) or completely saturated 3-6 membered ring comprising 3-5C and 1-3 heteroatoms of O, S or N, where the ring is substituted by n residues of halo, 1-4C-alkyl or 1-4C-alkox
