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Dissipation of Clopyralid and Picloram in Soil and Seep Flow in the Blacklands of Texas

USDA-ARS, Southern Crops Res. Lab., Pest Control and Application Systems Technology Unit, Dep. Range Science, Texas A&M Univ., College Station, TX 77843;

C. W. Richardson

USDA-ARS, Grassland, Soil & Water Research Lab., 808 East Blackland Road, Temple, TX 76502.

^* Corresponding author.

ABSTRACT

The dissipation, leaching and movement of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) and picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) were determined in soil and subsurface water after spray application of the herbicides to the surface of an area overlying a shallow perched water table in the Blacklands of Texas. A 1:1 mixture of the monoethanolamine salt of clopyralid and the tri-isopropanolamine salt of picloram was applied at 0.56 kg a.i./ha each in May 1988 and June 1989 on the same area. Approximately 90 d after treatment, >99% of the clopyralid and >92% of the picloram had dissipated. Most herbicide was detected in the upper 30 cm of soil. No herbicide was detected in subsurface water from the area treated in 1988, but concentrations of <6 mg/m³ of clopyralid and <5 mg/m³ of picloram were detected in subsurface water collected 11 and 41 to 48 d after treatment in 1989.

Mention of trademark name of proprietary product does not constitute a guarantee or warranty of the product by the USDA or Texas A&M Univ. and does not imply its approval to the exclusion of other products that may also be suitable.

Received for publication June 25, 1990.