Metribuzin and the ethyl ester of chlorimuron were evaluated alone and in combination for preemergence broadleaf weed control in soybeans. Neither herbicide alone controlled all broadleaf weeds tested, but combinations showed both complementary and additive action. Two field studies quantified these interactions on broadleaf weeds and showed that low rates of either herbicide alone controlled Pennsylvania smartweed and redroot pigweed. Metribuzin was more effective than chlorimuron in controlling prickly sida and hemp sesbania, while chlorimuron was more effective on common cocklebur, sicklepod, and ivyleaf and pitted morningglories. Additive action was most important on velvetleaf, sicklepod, annual morningglories, and hemp sesbania. Because the components were both additive and complementary, a range of mixture rates and ratios were more effective for weed control than either herbicide alone.
