A herbicidal composition which comprises as an active ingredient a herbicidally effective amount of a triazinone compound of the formula: ##STR1## wherein A is --NH--N.dbd.CHCH.sub.2 NH--, --NH--NHCH.sub.2 CH.sub.2 NH-- or --NH--N.dbd.CHC(NHOH).dbd.N--, and an inert carrier.