| Since the introduction of quinclorac into Arkansas rice production, quinclorac drift and multiple-resistance of barnyardgrass to both quinclorac and propanil have become major concerns. Studies were conducted to evaluate the effects of quinclorac on tomato growth and development. In general, increasing quinclorac rate and number of applications increased tomato injury, which correlated with plant fresh weight and yield. Quinclorac residues were greatest in tomato tissue immediately after application and declined with time. Residue detection data indicated that tomato plant response was more sensitive than analytical equipment. Quinclorac half-life in tomato tissue ranged from 2.3 to 5.2 d after application, and generally increased as herbicide rate and number of applications increased. In both vegetative and flowering plants, the majority 14C-quinclorac remained in the treated leaf and developing leaves above the treated leaf were the strongest sink for 14C-quinclorac translocation. The flowering cluster of the tomato plants contained 1% of the total absorbed 14C-quinclorac. Trends of 14C-quinclorac movement throughout the various plant stages were similar. Other studies were conducted to evaluate possible mechanisms of resistance in propanil quinclorac resistant barnyardgrass. Absorption of 14C-quinclorac did not differ between resistant and susceptible barnyardgrass plants, but more radiolabeled quinclorac remained in the treated leaf of susceptible barnyardgrass (55% of the total absorbed) compared to the propanil-quinclorac resistant barnyardgrass (40% of the total absorbed). Furthermore, 1-aminocyclopropane-1-carboxylic acid and ethylene production was 2.5 and 10 times greater, respectively, in treated susceptible barnyardgrass compared to treated propanil-quinclorac resistant barnyardgrass. Both biotypes showed similar gravitropic responses when left untreated. Picloram treatment resulted in no gravimetric response and was speculated to be competing with IAA on auxin-binding protein sites. When plants were treated with quinclorac, the susceptible plant showed no gravitropic response, but resistant plant showed a gravitropic response. Results indicated that picloram and quinclorac interact differently with the auxin binding protein. Furthermore, an alteration has potentially occurred in the auxin binding proteins of the multiple-resistant barnyardgrass that yields sensitivity to IAA and picloram, but not quinclorac. |
