Absorption, translocation, metabolism, and spray retention of quinclorac in Digitaria sanguinalis and Eleusine indica

Absorption, translocation, and metabolism studies using C-14-quinclorac wer e conducted with quinclorac-sensitive Digitaria sanguinalis and quinclorac- tolerant Eleusine indica at the one- to two-tiller growth stage cultured un der hydroponic conditions. After an 80-h exposure time, both species had ab sorbed nearly equal amounts of C-14-quinclorac (27 and 22% for D. sanguinal is and E. indica, respectively). Over the exposure period, the absorption c urve for D. sanguinalis was curvilinear, with the maximum absorption occurr ing 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 C-14-quinclorac remained in the treated lea f for D. sanguinalis after 80 h. However, only 58% of the absorbed C-14 rem ained in the treated leaf of E. indica. Most of the C-14 translocated out o f the leaves moved to the tiller, the crown, and new leaf tissue. There was no appreciable exudation of C-14-quinclorac by either species during the a bsorption 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. sanguin alis (sensitive). Overall results suggested that a large difference in tole rance of the two species to quinclorac involves mechanisms other than absor ption, metabolism, or spray retention.