PERSISTENCE OF TRICLOPYR AND 2,4-D IN FLOODED AND NONFLOODED SOILS

Field studies were conducted on silt loam and silty clay soils to determine the persistence of triclopyr ([(3,5,6-trichloro-2-pyridinyl) oxy] acetic acid) and 2,4-D (2,4-dichlorophenoxy acetic acid) in the soil and water associated with rice (oryza sativa L.) production in Arkansas. Liquid formulations of these herbicides were applied postemergence to (i) paddy rice, (ii) rainfed lowland rice, and (iii) bare ground. Samples of soil and water were taken at various intervals until 49 days after application (DAA) and analyzed by gas chromatography. Dissipation of both herbicides was rapid with initial dissipation of 50% of the initial concentration, DT(50)s, in paddy water, dryland-rice soil, and bareground soil being 10 d or less. Neither herbicide was detected in water later than 28 DAA. Both herbicides were slightly more persistent In soil than in water. 2,4-D was slightly more mobile in the soil of all three cultural systems.