The protection of crops from weeds and other vegetation which inhibit crop growth is a constantly recurring problem in agriculture. To help combat this problem, researchers in the field of synthetic chemistry have produced an extensive variety of chemicals and chemical formulations effective in the control of such unwanted growth. Chemical herbicides of many types have been disclosed in the literature and a large number are in commercial use.
In some cases, active herbicides have been shown to be more effective in combination than when applied individually. The result is often termed "synergism" since the combination demonstrates a potency or activity level exceeding that which it would be expected to have, based on a knowledge of the individual potencies of the components. The present invention resides in the discovery that certain substituted ureas and certain pyrrolidones, already known individually for their herbicidal potency, display this synergistic effect when applied in combination.