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Which herbicides are used in forest vegetation management?

Category: Vegetation Management

There are five herbicide active ingredients registered for use in Canadian forestry: Glyphosate, Triclopyr, Hexazinone, 2,4-D, and Simazine. In Canadian forestry, glyphosate-based herbicides have been used on over 96% of the forest area treated in the past decade.

There are five herbicide active ingredients registered for use in Canadian forestry (glyphosate, triclopyr, hexazinone, 2,4-D and simazine). In Canadian forestry, glyphosate-based herbicides account for more than 96% of the forest area treated with herbicides in the past decade. Uses of other herbicides, particularly in recent years, are sufficiently minor that they do not warrant further discussion here (statistics on pesticide use in Canadian forestry are freely available through the National Forestry Database Program website, http://nfdp.ccfm.org/). Since the patent has expired on glyphosate, several manufacturers now produce various end-use formulations of this compound, sold in the forestry market under trade names such as VisionMax, Forza, Vantage and Weed-Master (Mihilovich et al. 2004). While all of these formulated products contain glyphosate as the active ingredient and a surfactant to enhance uptake across plant leaf cuticles, the actual chemical constitution of each formulation may vary (i.e., one formulated glyphosate product does not necessarily equal another).

There are three key reasons that glyphosate-based herbicides are so dominant in Canadian and international forestry and agriculture: a) its excellent record of efficacy and reliability in controlling most competitive species including those that resprout through rhizomes, roots or basal buds; b) its favourable environmental behaviour profile (e.g., non-persistent in soils, vegetation and water, does not accumulate in animals, has very low potential to leach into ground water) (How long does glyphosate remain in the soil, water, plants and sediments after treatment?); and c) its low innate toxicity to humans and wildlife (What are environmental and health regulators saying about IARC’s glyphosate classification?). In forestry applications, glyphosate does not easily kill conifers, particularly after they have had a chance to fully develop a waxy cuticle on their needles (usually near the end of August). This cuticular wax is sufficiently thick to protect the needles from disease, dehydration and the effects of glyphosate at doses that would otherwise be sufficient to injure the tree. Thus, glyphosate-based herbicides are particularly effective at controlling competition from undesired broadleaf vegetation that is immediately adjacent to young conifers.

Glyphosate-based products similar to those used in Canadian forestry are registered and used in more than 160 countries and play critical roles in the production of more than 100 terrestrial food crops, including wheat, corn and soybeans (http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2009-0361-0003). While agricultural applications of glyphosate-based herbicides account for the majority of glyphosate use (75% by volume), these same herbicides are also important for vegetation control in residential home and garden (15%), industrial site management and rights of way (6%) and, of course, forestry (4%) applications (Michael Cunningham, Engage Agro, personal communication).

Mihajlovich, M., Pitt, D.G., Blake, P. 2004. Comparison of four glyphosate formulations for white spruce release treatment. Forestry Chronicle 80(5): 608-611.