DEPOSITION AND DISSIPATION OF 3 HERBICIDES IN FOLIAGE, LITTER, AND SOIL OF BRUSHFIELDS OF SOUTHWEST OREGON

The herbicides 2,4-D ((2,4-dichlorophenoxy)acetic acid), triclopyr ([(3,5,6-trichloro-2-pyridinyl)-oxy]acetic acid), and picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) were applied by helicopter to test grids in mountainous southwestern Oregon brushfields on shallow, rocky, clay loam soils. Herbicide concentrations were observed in crown twigs and foliage, browse twigs and foliage, litter, and soil. Initial deposits in the target area ranged from 61 to 115% (average 82%) of the nominal dosage, with coefficients of variation of 29-104%. Initial concentrations in crown foliage were 44 mg/kg for each kilogram per hectare applied; deposits on browse foliage and litter were 38% and 74%, respectively, of crown concentrations. Early after application, decreases were more rapid for salt formulations than for esters. After 79 days, decrease of all herbicides was slight in foliage, but continued in soil. Picloram disappeared most rapidly and was least mobile, followed by triclopyr and 2,4-D. Triclopyr and 2,4-D remained nearly constant in foliage through winter. Disappearance was rapid in litter. © 1990, American Chemical Society. All rights reserved.