Picloram Movement in an Appalachian Hardwood Forest Watershed

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Abstract
Picloram (4‐amino‐3,5,6‐trichloropicolinic acid) was applied at a rate of 5.0 kg ha−1 acid equivalent to 4 ha of the 28‐ha Watershed 19, Coweeta Hydrologic Laboratory in western North Carolina. The herbicide was broadcast manually as a pellet formulation (10% acid equivalent) in May 1978. The objective was to eliminate a poor‐quality mixed oak overstory and rhododendron (Rhododendron maximum L.)‐laurel (Kalmia latifolia L.) understory prior to planting white pine (Pinus strobus L.). Picloram residues in samples from an Umbric Dystrochrept soil peaked in concentration in the upper 0.07 m at 11.58 mg kg−1, 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 (peak of 350 mg m−3). Picloram residues were detected in soil solution 1.2 m into the soil, but concentrations were < 25 mg m−3, and persisted for only 60 weeks. Intensive sampling of two springs detected trace levels for a period of 18 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.
Funding Information
  • U.S. Department of Agriculture