The use of herbicides to reduce weed competition in the establishment of forest stands is increasing in British Columbia (Henigman 1986). A common concern about the use of herbicides is their effect on water quality. To address this concern, a program was undertaken in the Revelstoke area to monitor herbicide residues in surface water draining a cutblock on which Roundup® was operationally applied.
Roundup®, whose active ingredient is glyphosate (N-[phosphonomethyl] glycine), is relatively new to operational forestry applications. Originally it was introduced by Baird et al. (1971) for use in agriculture. Glyphosate is a broad spectrum, relatively non-selective herbicide that effectively controls most annual and biennial herbaceous plants and some deep rooted perennial species (Weed Science Society of America 1979). Application is made as a post-emergence spray to the target vegetation. Uptake is through the foliage, from where the herbicide is translocated through the plant. Studies related to glyphosate have been compiled by Chykaliuk et al. (1981). As well, the U.S. Department of Agriculture Forest Service (1984) prepared a detailed information review on the toxicology, environmental fate, and hazard assessment of glyphosate.
Norris et al. (1983) described several pathways for herbicide residues to enter water: direct application, drift, mobilization in ephemeral stream channels, overland flow, and/or leaching. To minimize the movement of herbicides through these pathways, pesticide use permits in British Columbia require a 10-m pesticide-free zone (PFZ) surrounding all water courses. In addition, current practice involves using a 100-m or wider buffer around water courses where aerial application of herbicide is planned.
Witt has suggested that the measurement of glyphosate residues in surface water indicates off-site movement, and is cause for re-evaluation of the application program. Little information exists in southeastern British Columbia on the movement of glyphosate under local conditions.
The objective of this study was to assess the off-site movement of glyphosate and its metabolite AMPA (amino-methyl-phosphonic acid), following an operational application of Roundup®, by monitoring a surface water source for residues of the herbicide.
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Updated November 14, 2008