Summary:The effects of asulam applied in September 1970 at 0.55, 1.12 and 2.24 kg a.i./ha onRumex obtusifolius(L.),Lolium perenne(L.), Other grasses andTrifolium repens(L.) growing in two swards in Wales were investigated. Good short‐term control ofRumexwas achieved by all rates of asulum although regeneration was occurring by the spring following treatment. Dry matter yields of L.perennewere slightly lowered by 2.24 kg a.i./ha 6 weeks after spraying but production in the spring following treatment was substantially greater than on untreated plots.Poa trivialis(L.) andAgrostis stolonifera(L.) were substantially reduced but invasion of the bare spaces by P.trivialisandP. annua(L.) seedlings tended to mask the success of this control. No harmful effects on T. repens were recorde