Low picloram concentrations in streamflow resulting from forest application of Tordon-10K

Neary, D.G.; Douglass, J.E.; Fox, W.

Proceedings of the 32nd Annual Meeting of the Southern Weed Science Society: 182-197


Accession: 000693208

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Tordon-10K (picloram-potassium 10% pellets) were applied to 4 ha of a watershed at Franklin, N. C., to prepare a low-quality hardwood stand for planting eastern white pine (Pinus strobus). The herbicide was applied in May 1978 at 5 kg a.i./ha. Although application was followed by dry weather conditions, 76% of the overstorey plants and 95% of the rhododendron (Rhododendron sp.) and laurel (Kalmia latifolia) in the understorey were initially affected. Probably because of drought, only 30% of the overstorey and 20% of the understorey plants were killed. During the first 5 months after application, soil solution at 30 cm contained <10 p.p.b. picloram until heavy rains in Aug.; then, a peak of 174 p.p.b. was measured. At 60 cm, picloram peaked 2 months later at 179 p.p.b. In the soil solution sampled at 120 cm, picloram concns. never exceeded 3 p.p.b. Picloram was only detected twice (late June and early July) in streamflow, and the max. concn. was only 8 p.p.b. After heavy rains in Aug. totalling nearly 290 mm, no picloram was detected in streamflow. No major leaching of anions or cations has been evident in soil solution or streamflow. On the basis of this early data obtained during an intermittently dry summer, it is concluded that well-controlled applications of Tordon-10K made to ridges and upper slopes should not produce any significant pollution of streams draining the deep soil systems of the southern Appalachians. From summary.