Decay of Quinclorac in Acidic Paddy Soil and Risk Evaluation to the Subsequent Crop, Tobacco ( Nicotiana tabacum L.)

Quinclorac is a selective herbicide commonly used in China to control monocotyledonous weeds in paddy fields. A field experiment was conducted to quantify the environmental behavior of quinclorac in acidic paddy soil under rice ( Oryza sativa L.) field conditions, and to evaluate the risk of its residues to the subsequent crop of tobacco ( Nicotiana tabacum L.). Rice was sprayed once with quinclorac 50% WP at 562.5, 375.0, or 187.5 g a.i. ha −1 at 7 days after transplanting the seedlings. Decay of quinclorac in paddy field soil followed first-order kinetics, with a half-life of 28.29–30.27 days. At harvest time, 0.090, 0.074 and 0.034 mg kg −1 of quinclorac were found in soils following the above-described treatments, respectively. Leaves of the subsequent crop, tobacco, sown the year after the quinclorac treatments, exhibited different dose-dependent degrees of visible phytotoxicity symptoms.