RESIDUES OF 2,4-D AND PICLORAM IN ASPEN POPLAR AND SOIL AFTER APPLICATION WITH A ROLLER

Abstract

The use of wipers to apply herbicides to brush regrowth in pastures has been suggested as a way of reducing damage to the forage understory. Estimates of picloram in the soil around the base of Aspen poplar (Populus tremuloides Michx.) regrowth and of picloram and 2,4-D in poplar tissues were made 84 and 39 d, respectively, after using a roller to apply these herbicides in a 7.3:1 2,4-D:picloram (acid equivalent) mixture to the brush. Bioassay revealed that between 11 and 16% of the picloram applied reached the soil and that, when the herbicide mixture was applied at a high enough concentration to kill the trees, sufficient picloram reached the soil around them to affect legume establishment. Chemical assay revealed that only about 2% or less of the picloram and 2,4-D applied remained in the poplar tissue and that greater than 80% of this was in the leaves — the primary application surface. These residues are unlikely to cause problems in the environment because of the small quantities and the slow release from poplar tissue by leaching and decay. The remainder of the applied picloram and 2,4-D was unaccounted for and was assumed lost through metabolism and photochemical degradation.Key words: 2,4-D, picloram, aspen poplar, soil, roller applicator