An experiment was performed at the AES-UPR Gurabo Substation to evaluate atrazine, simazine, diuron, and tebuthiuron for preemergence control of weeds in a stargrass pasture. Tebuthiuron at 3.36 kg a.i./ha was the most effective, and tebuthiuron at 1.68 kg a.i./ha was the second most effective. The remaining herbicides also provided satisfactory weed control. At 3.36 kg a.i./ha, tebuthiuron was somewhat phytotoxic to stargrass, but less so at 1.68 kg a.i./ha. None of the other herbicides produced severe stargrass injury. Stargrass yield was not affected by any of the herbicides. Crude protein content of stargrass was not affected by any herbicide tested.