Dissipation and offsite movement of forestry herbicides in plants of importance to Native Americans in California National Forests

Ando, C.; Segawa, R.; Gana, C.; Li, L.; Walters, J.; Sava, R.; Barry, T.; Goh, K. S.; Lee, P.; Tran, D.; White, J.; Hsu, J.

doi:10.1007/s00128-003-0171-5

A study was conducted over a 4-year period (1997-2001) in Eldorado, Sierra, and Stanislaus National Forests, California, USA, to investigate the dissipation and offsite movement of glyphosate, triclopyr and hexazinone in bracken fern (Pteridium aquilinum var. pubescens) roots, buckbrush (Ceanothus cuneatus) shoots, golden fleece (Ericameria) foliage and manzanita (Arctostaphylos spp.) berries. The herbicides showed a general decline trend in concentration over time. Glyphosate application-day residue means ranged from 0.5 to 241 micro g/g for bracken fern roots, buckbrush shoots, golden fleece foliage and manzanita berries. Triclopyr was detected on application-day in all media sampled including bracken fern root with mean levels ranging from 0.1 to 19 micro g/g. Liquid hexazinone applications resulted in higher mean application-day residue levels in buckbrush shoots, bracken fern roots and golden fleece foliage (0.2 to 81 micro g/g) compared with granular hexazinone (non-detected to 0.3 micro g/g). The average herbicide half-lives ranged from 1 to 19 weeks for various plat part/herbicide product combinations. Half-lives were longest for bracken fern roots relative to other plant parts sampled. Residues of glyphosate, triclopyr and hexazinone were detected outside the treatment area following application to bracken fern roots, buckbrush shoots and deerbrush shoots. Residues ranged from non-detected to 2.7 micro g/g.