Pyridazinone compound or its salt, and herbicide containing it

A pyridazinone compound represented by the formula (I) or its salt:

• wherein X is —O— and Q is bicyclic heteroaryl which may be substituted by Z;
• or X is —S—, —SO—, —SO2— or —N(Y)— and Q is monocyclic aryl which may be substituted by Z, monocyclic heteroaryl which may be substituted by Z, bicyclic aryl which may be substituted by Z, or bicyclic heteroaryl which may be substituted by Z
• Y is a hydrogen atom or alkyl;
• R1 is alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl, haloalkyl, monocyclic aryl which may be substituted by Z, monocyclic arylalkyl which may be substituted by Z, alkylthioalkyl, alkylsulfinylalkyl, alkylsulfonylalkyl, dialkylaminoalkyl, alkoxyalkyl, amino, nitro, alkylcarbonylalkyl, alkoxycarbonylalkyl or hydroxycarbonylalkyl;
• R2 is a hydrogen atom, alkyl, haloalkyl, cycloalkyl, halogen, alkoxy, alkylthio, alkylsulfinyl, alkyl sulfonyl or cyano;
• R3 is halogen, hydroxy, alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkoxy, haloalkoxy, nitro, amino, alkylcarbonyl or cycloalkyl;
• R4 is a hydrogen atom, alkyl, —C(O)R6, —C(S)R6, —SR7, —SOR7, —SO2R7, monocyclic arylalkyl which may be substituted by Z, alkoxyalkyl, —CH(J1)OCOOJ2, alkylcarbonylalkyl, monocyclic aryl which may be substituted by Z, monocyclic arylcarbonylalkyl which may be substituted by Z, alkenyl, alkoxyalkoxyalkyl, alkoxycarbonylalkyl, alkynyl, cyanoalkyl, haloalkoxyalkyl or dialkylaminoalkyl;
• R6 is alkyl, alkoxy, morpholino, dialkylamino, (monocyclic aryl which may be substituted by Z)(alkyl)amino, cycloalkyl, alkoxyalkyl, alkylthioalkyl, haloalkyl, alkylthio, alkenyl, alkynyl, alkoxycarbonylalkyl, cycloalkylalkyl, cyanoalkyl, alkoxyalkoxyalkyl, monocyclic aryl which may be substituted by Z, monocyclic heteroaryl which may be substituted by Z, monocyclic arylalkyl which may be substituted by Z, monocyclic aryloxy which may be substituted by Z, monocyclic arylthio which may be substituted by Z, monocyclic aryloxyalkyl which may be substituted by Z, monocyclic arylthioalkyl which may be substituted by Z, alkoxycarbonyl, alkoxyalkoxy, haloalkoxy, haloalkoxyalkoxy, alkylthioalkoxy, cycloalkoxyalkoxy, monocyclic arylalkoxy which may be substituted by Z, monocyclic aryloxyalkoxy which may be substituted by Z, monocyclic heteroaryloxyalkoxy which may be substituted by Z, alkenyloxyalkoxy, alkoxyalkoxyalkoxy, alkynyloxy, alkenyloxy, haloalkenyl, dialkylaminoalkyl, alkylthioalkoxyalkoxy, cycloalkylalkoxy, cycloalkylalkoxyalkoxy, monocyclic arylalkoxyalkoxy which may be substituted by Z, monocyclic heteroarylalkoxyalkoxy which may be substituted by Z or cycloalkoxy which may be substituted by Z;
• R7 is alkyl, haloalkyl, cycloalkyl or monocyclic aryl which may be substituted by Z;
• Z is halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, cycloalkyl, cyano, nitro, —C(O)OR5, formyl, alkylthio, alkylsulfinyl, alkyl sulfonyl, —CH═NOJ3 or dialkylaminocarbonyl;
• R5 is a hydrogen atom or alkyl;
• J1 is a hydrogen atom or alkyl;
• J2 is alkyl or cycloalkyl;
• J3 is a hydrogen atom, alkylcarbonyl or alkoxyalkyl;
• and
• n is an integer of from 0 to 4.