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Picloram Movement in an Appalachian Hardwood Forest Watershed¹

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.

Key Words: water quality • herbicide • groundwater • streamflow

¹ This work was jointly supported by the USDA Forest Service Southeastern Forest Exp. Stn. and Southern Region, the Univ. of Georgia, Athens, and Dow Chemical Company, Midland, MI.

² Soil scientist, Southeastern Forest Exp. Stn. and Soil Science Dep., Univ. of Florida, Gainesville, FL 32611; pesticide residue chemist, Extension Poultry Science Dep., University of Georgia, Athens, GA 32601; hydrologist (retired), Coweeta Hydrologic Laboratory, Otto, NC 28763; and professor, Microbiology Dep., South Dakota State Univ., Brookings, SD 57007.

This publication reports research involving pesticides. It does not imply that the uses discussed here have been registered. All uses of pesticides must be registered by appropriate state and/or federal agencies before they can be recommended.

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or wildlife—if they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for the disposal of surplus pesticides and pesticide containers.