Picloram movement in an Appalachian hardwood forest watershed.

Picloram was applied at a rate of 5.0 kg/ha acid equivalent to 4 ha of a 28-ha watershed on Coweeta. Herbicide was broadcast manually as pellets to eliminate a poor-quality mixed oak overstory and rhododendron-laurel understory prior to planting white pine. Picloram residues in soil samples peaked in concentration in the upper 0.07 m, had a half-life of about 4 weeks, and declined to near detection limits 28 weeks after application. Soil solution contained the highest picloram levels at 0.6 m. Picloram residues were detected in soil solution 1.2 m into the soil, but concentrations were < 25 mg/m3, and persisted for only 60 weeks. Intensive sampling of two springs detected trace levels for a period of 8 d. Only sporadic, low-level picloram residues were detected in streamflow from nested 10-ha and 28-ha watersheds during a 70-week period. Use of the herbicide picloram did not affect the quality of streamflow from Watershed 19 for domestic or agricultural purposes.