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Picloram in Water and Soil from a Semiarid Pinyon-Juniper Watershed¹

ABSTRACT

A mixture of picloram (4-amino-3,5,6-trichloropicolinic acid) at 2.8 kg acid equivalent (ae)/ha and 2,4-D [(2,4-dichlorophenoxy) acetic acid] at 5.6 kg acid equivalent/ha was aerially applied onto 113 ha of a 146-ha pinyon-juniper watershed [Juniperus osteosperma (Torr.) Little and Pinus edulis Engelm., respectively] in north-central Arizona. Picloram residues in runoff water and soil were monitored. Picloram was detected in runoff water leaving the treated area for 30.5 months after application. The highest concentration, 320 ppbw, was in the initial runoff after treatment. A total of 1.1% of the picloram applied left the treated area in runoff water. Picloram was not detected farther than 5.6 km downstream. The picloram concentration was relatively constant during runoff events unless water from snow melt or from an untreated area mixed with the runoff from the treated area. Less picloram came from an area with individually treated trees than from an area with broadcast application. Dip (grab), single-stage flood, or splitter-box water samples all gave comparable picloram contents from the same location with the same runoff event. Picloram was detected in the soils for 44 months, mainly below the 45-cm depth down to bedrock at 122 cm.

Key Words: pollution • herbicides • water quality • dissipation

¹ Contribution from Agric. Res., Sci. and Educ. Admin., USDA.

² Research Agronomist, USDA-SEA-AR, 2000 East Allen Road, Tucson, AZ 85719.

Received for publication October 9, 1979.