Herbicidal composition and weeding method

A method for controlling weeds which comprises applying a herbicidal composition in a dosage chosen in the range of 1 g to 5 kg (in terms of the active ingredients of the composition) per 10 ares for controlling undesirable weeds, said herbicidal composition comprising as active ingredients a synergistic effective amount of at least one organophosphorous compound and a synergistic effective amount of a 3-substituted phenylpyrazole derivative represented by the general formula (I):

• ##STR5## wherein R is
• Y.sup.1 R.sup.3
• (wherein R.sup.3 is a lower alkyl group, a lower haloalkyl group, a lower alkenyl group or a lower alkynyl group, and Y.sup.1 is --O-- or --S--),
• --Y.sup.2 CH(R.sup.4)CO--OR.sup.5
• (wherein R.sup.4 is a hydrogen atom or a lower alkyl group, R.sup.5 is a hydrogen atom, a lower alkyl group, a lower haloalkyl group, a lower alkenyl group or a lower alkynyl group, and Y.sup.2 is --O--, --S-- or --NH--),
• --COOCH(R.sup.4)CO--Y.sup.1 R.sup.5
• (wherein R.sup.4, R.sup.5 and Y.sup.1 are as defined above), or
• --COOR.sup.6
• (wherein R.sup.6 is a lower alkyl group, a lower alkenyl group or a lower alkynyl group), R.sup.1 is a lower alkyl group, R.sup.2 is a hydrogen atom, a lower alkyl group or a lower haloalkyl group, X.sup.1 and X.sup.2, which may be the same or different, are halogen atoms, Y is --O--, --S--, --SO-- or --SO.sub.2 --, and n is zero or 1.

A method for controlling weeds which comprises the steps of applying a herbicidal composition in a dosage chosen in the range of 1 g to 5 kg, in terms of the active ingredients of the composition, per 10 ares for controlling undesirable weeds, said herbicidal composition comprising as active ingredients at least one herbicidal organophosphorus compound at a dosage insufficient to control weeds as a sole active ingredient and a synergistic effective amount of a 3-substituted phenylpyrazole derivative represented by the formula (I):

• ##STR6## wherein R is
• --Y.sup.1 R.sup.3
• wherein R.sup.3 is a lower alkyl group, a lower haloalkyl group, a lower alkenyl group or a lower alkynyl group, and Y.sup.1 is --O-- or --S--,
• --Y.sup.2 CH(R.sup.4)CO--OR.sup.5
• wherein R.sup.4 is a hydrogen atom, or a lower alkyl group, R.sup.5 is a hydrogen atom, a lower alkyl group, a lower haloalkyl group, a lower alkenyl group or a lower alkynyl group, and Y.sup.2 is --O--, --S-- or --NH--,
• --COOCH(R.sup.4)CO--Y.sup.1 R.sup.5
• wherein R.sup.4, R.sup.5, and Y.sup.1 are as defined above, or
• --COOR.sup.6
• wherein R.sup.6 is a lower alkyl group, a lower alkenyl group or a lower alkynyl group, R.sup.1 is a lower alkyl group, R.sup.2 is a hydrogen atom, a lower alkyl group or a lower haloalkyl group, X.sup.1 and X.sup.2, which may be the same or different, are halogen atoms, Y is --O--, --S--, --SO-- or --SO.sub.2 --, and n is zero or 1.