Physiological Basis for Triazine Herbicide Tolerance in Bermudagrass, Seashore Paspalum, and Zoysiagrass

Abstract

ABSTRACTAtrazine and simazine control weeds in warm‐season turfgrasses, but excessive injury limits applications to sensitive species. The objective of this research was to evaluate the physiological basis for differential tolerances of bermudagrass (Cynodon dactylon (L.) Pers.), seashore paspalum (Paspalum vaginatum Sw.), and zoysiagrass (Zoysia japonica Steud.) to atrazine and simazine. In greenhouse experiments, hierarchical shoot mass reductions from the nontreated by species were: seashore paspalum > bermudagrass > zoysiagrass for atrazine and seashore paspalum > bermudagrass = zoysiagrass for simazine. Atrazine and simazine treatments to soil only or foliar plus soil reduced shoot mass similarly, averaging 45% from nontreated, while foliar‐only treatments reduced shoot mass 22% from the nontreated. Species rank for root absorption of both herbicides after 48 h from high to low was seashore paspalum > bermudagrass > zoysiagrass. All species had acropetal translocation of 14C‐atrazine and 14C‐simazine, but bermudagrass and zoysiagrass translocated ∼10% more 14C than seashore paspalum after 48 h. Hierarchical species rank for nonmetabolized 14C‐atrazine translocation to shoots after 8 h from high to low was seashore paspalum > bermudagrass > zoysiagrass. All species metabolized 14C‐atrazine to hydroxyatrazine and two unidentified metabolites in root and shoots. All species metabolized simazine to hydroxysimazine and two other metabolites in shoots. Seashore paspalum had less total metabolism of 14C‐simazine than bermudagrass and zoysiagrass and produced fewer metabolites in roots. Results suggest bermudagrass and seashore paspalum susceptibility to atrazine is associated with greater absorption and translocation of the parent herbicide to shoots than zoysiagrass. Seashore paspalum susceptibility to injury from simazine is associated with differences in absorption and metabolism from tolerant turfgrasses bermudagrass and zoysiagrass.