Picloram Movement in Soil Solution and Streamflow from a Coastal Plain Forest
Picloram (4-amino-3,5,6-trichloropicolinic acid) was aerially applied to P longleaf pine (Pinus palustris L.) site in the upper constnl plain of Alabama to control kudzu [Purraria lobota (Willd.) Ohwi]. Pellets (10% a.i.) were spread at the rate of 56 kg ha-1 on loamy sand Typic Knnhspludult soils. Movement of this herbicide was monitored with mineral soil samples, tension-cup lysimeters, flow- proportional streamilow samplers, and discrete samplers. Piclornm levels in the upper 15 cm of mineral soil peaked at 0.96 to 2.25 mg kg-1 25 d after application, depending on slope position, and declined to 0.13 to 0.29 mg kg-1 1 yr later. In soil solution, picloram was detected at P depth of 0.4 m between 26 and 273 d after application.Only 4 of IS lysimeters consistently contained detectable residues. Maximum picloram levels in soil solution were 130, 450, and 191 mg m-3 for ridge, midslope, and toe-slope positions, respectively. Downstream monitoring began 4 d after the herbicide application, and art initial concentration of 68 mg m-3 of picloram was detected. The maximum downstream concentration of 77 mg m-3 occurred 18 d after the application, immediately after the second storm event. Downstream levels dropped to <10 mg m-3 after 90 d and to <2 mg m-3 after 200 d. Following localized retreatment along the steam more than a year after the initial treatment, levels climbed again into the 20 to 30 mg m-3 range. Most of the initial off-site movement came from B perennial stream that had been inadvertently treated, but subsequently storm runoff was the largest contributor to stream contaminntioion. Picloram residues in this streeam were similar to those observed downstream, but they were higher (up to 241 mg m-3 and dropped faster to below 2 mg m-3 after D 150.