The invention relates to a herbicidal and plant growth regulating composition which contains as active ingredient a 2-benzoyl-2-phenyloxirane of formula I ##STR1## wherein each of m and n independently of the other is 0, 1, 2 or 3 and each of R and R' independently of the other is a halogen atom, a C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 haloalkyl or C.sub.1 -C.sub.4 haloalkoxy group or the nitro or cyano group or a phenoxy group which is substituted by (R).sub.m, in the form of a racemate or an optically active enantiomer.Some oxiranes are known as intermediates for the preparation of fungicides and others are novel. The herbicidal composition has selective action in rice crops and is active against grasses.