Date of this Version
Weed Science. 36:436‑440
Atrazine metabolism was studied in four warmseason forage grasses to determine if metabolism was the basis for differential atrazine tolerance among the grasses. Big bluestem and switchgrass are atrazine tolerant while indiangrass and sideoats grama are atrazine susceptible in the seedling stage. Metabolism of atrazine in big bluestem and switchgrass occurred primarily by glutathione conjugation. The major metabolic product isolated from indiangrass and sideoats grama was the N-deethylated metabolite of atrazine. Glutathione conjugation by big bluestem and switchgrass occurred at a faster rate than N-dealkylation of atrazine in indiangrass and sideoats grama. Differential tolerance to atrazine among the grasses studied was probably due to the metabolic route by which they detoxify atrazine and the rate of metabolism for that specific route. Intraspecific differences in atrazine tolerance in indiangrass were due to the amount of metabolite produced in relationship to the amount of parent atrazine remaining in the shoot tissue. The more tolerant indiangrass lines had a higher metabolite to parent atrazine ratio than susceptible lines. This study confirmed differences in seedling atrazine tolerance of four indiangrass lines observed in previous greenhouse studies. Nomenclature: Atrazine, 6- chloro -N- ethyl - N' -(1- methylethyl) -1,3,5 -triazine- 2,4-diamine; big bluestem, Andropogon gerardii Vitman; switchgrass, Panicum virgatum L.; indiangrass, Sorghastrum nutans (L.) Nash; sideoats grama, Bouteloua curtipendula (Michx.) Torr.