Metabolism and Differential Susceptibility of Crabgrass and Witchgrass to Simazine and Atrazine

Growth chamber studies showed crabgrass [Digitaria sanguinalis(L.) Scop.] to be more tolerant than witchgrass (Panicum capillareL.) to simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Both grasses were more susceptible to simazine than to atrazine. Thes-triazines were taken up by both weed species in equal quantities, but witchgrass translocated larger amounts of simazine and atrazine to the shoots. The greater sensitivity of witchgrass to simazine appeared to be due to the increased translocation of unchanged simazine to the shoots. Greater sensitivity of witchgrass to atrazine was attributed to increased translocation of atrazine to the shoots and less metabolism of thes-triazine to hydrophilic metabolites. It was concluded that the hydrophilic metabolites were the peptide conjugates formed by the enzyme glutathione-S-transferase.