The present invention relates to herbicidal benzyloxy-substituted phenyl-diones and phenyl-dioxo-thiazinones of formula (I), as well as to herbicidal compositions comprising such compounds, and to the use of such compounds or compositions in controlling undesirable plant growth, in particular in controlling weeds, such as broad-leaved dicotyledonous weeds, in crops of useful plants. Formula (I), or a salt or N-oxide thereof, wherein A1 is N or CR1; A3 is C(O) or S(O)2; G is hydrogen or C(O)R6; R1, R3, X and Y are i.a. hydrogen, alkyl or haloalkyl; n is 0-5; each Z is i.a. alkyl, haloalkyl or alkoxy; and R6 is i.a. alkyl, alkenyl or alkynyl.