Picloram Persistence in Semiarid Rangeland Soils and Water

Residues in soil, following application of 0.25 lb/A of 4-amino-3,5,6-trichloropicolinic acid (picloram) to semi-arid rangelands, usually were restricted to the top 12 inches for 60 days. Five ppb or less picloram were detected below 12 inches at 120 to 180 days after application; but picloram usually dissipated from the soil profile within a year. More picloram was detected 5 months after application at 6 to 18 inches deep at the lower ends of plots with 3% slopes than in plots with 0, 1, or 2% slopes. Runoff water from plots irrigated 10 days after treatment contained 17 ppb picloram. Irrigation or rainfall at 20, 30, or 45 days after picloram application resulted in less than 1 ppb picloram in runoff water. No more than 1 or 2 ppb picloram were detected after dilution of runoff water in large ponds.