Absorption, translocation, and metabolism studies using 14C-quinclorac were conducted with quinclorac-sensitive Digitaria sanguinalis and quinclorac-tolerant Eleusine indica at the one- to two-tiller growth stage cultured under hydroponic conditions. After an 80-h exposure time, both species had absorbed nearly equal amounts of 14C-quinclorac (27 and 22% for D. sanguinalis and E. indica, respectively). Over the exposure period, the absorption curve for D. sanguinalis was curvilinear, with the maximum absorption occurring approximately 48 h after exposure. The response curve for E. indica was linear across the exposure period. Results from the translocation studies showed that 95% of the absorbed 14C-quinclorac remained in the treated leaf for D. sanguinalis after 80 h. However, only 58% of the absorbed 14C remained in the treated leaf of E. indica. Most of the 14C translocated out of the leaves moved to the tiller, the crown, and new leaf tissue. There was no appreciable exudation of 14C-quinclorac by either species during the absorption period. Results of the metabolism studies showed that neither the susceptible species (D. sanguinalis) nor the tolerant species (E. indica) metabolized the parent quinclorac herbicide. Spray retention studies showed that E. indica (tolerant) retained more applied quinclorac than D. sanguinalis (sensitive). Overall results suggested that a large difference in tolerance of the two species to quinclorac involves mechanisms other than absorption, metabolism, or spray retention.
Nomenclature: Quinclorac; Digitaria sanguinalis L. DIGSA, large crabgrass; Eleusine indica L. ELEIN, goosegrass.