Imazaquin was the first imidazolinone to be widely accepted as a herbicide for broad spectrum weed control. In 1981, field testing began in the U.S. and Brazil. Initial results demonstrated that imazaquin could be applied preplant incorporated, preemergence, or post-emergence for the control of many difficult-to-control weed species. In Brazil, excellent control of Euphorbia heterophylla was observed. In the U.S., a significant finding was that imazaquin soil-applied treatments provided excellent control oiXanthium strumarium, which was not controlled by standard preplant-incorporated or preemergence herbicides. In early testing, it was discovered that imazaquin applied as a postemergence treatment uniquely provided both burndown of susceptible weeds present and residual control of later germinating weeds.