Evaluation of Red Morningglory (Ipomoea coccinea) for Potential Atrazine Resistance1

Laboratory and greenhouse studies were conducted to determine if the reported red morningglory control failures with atrazine in sugarcane are caused by triazine-resistant mutants. Plants were grown from seeds collected at 24 locations in Louisiana and Arkansas where atrazine had never been used, and where it had been used in sugarcane with poor results. Terminal fluorescence of leaf material from all locations increased after treatment with 10−3 M atrazine, indicating electron transport inhibition and, hence, triazine susceptibility. However, small differences in the magnitude of fluorescence increase were observed among populations, possibly indicating the existence of biotypes with slightly different inherent tolerances to atrazine. Some phenotypic differences were observed among the red morningglory populations. In a separate study, postemergence application of atrazine at 1.1 kg ai/ha plus nonionic surfactant controlled greenhouse-grown plants from all populations at least 99%, which supports the fin...