Triclopyr, also Trichlopyr,[2] formally [(3,5,6-trichloropyridin-2-yl)oxy]acetic acid,[3] is an organic compound in the pyridine family of herbicides that is used as a systemic foliar type of herbicide[4][3] and, secondarily, as a fungicide.[5] Triclopyr is an acetic acid derivative, and so a monocarboxylic acid, with a pyridyloxy substiuent, specifically, a pyridin-2-yloxy group substituted by chloro groups at positions 3, 5 and 6.[3] It biological mechanism as an herbicide lies in its mimicking the action of the plant growth hormone, auxin.[6][bettersourceneeded]
Structure and chemistry
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Triclopyr is an acetic acid derivative, and so a monocarboxylic acid, with a pyridyloxy substiuent, specifically, a pyridin-2-yloxy group substituted by chloro groups at positions 3, 5 and 6.[3]
History
Triclopyr triethylammonium (TEA) was first registered in 1979 in the United States for use as an herbicide in non-crop areas and forestry to control broadleaf weeds and woody plants. A year later, in 1980, a formulation containing triclopyr butoxyethyl ester (BEE) was registered for similar applications. Both formulations expanded their usage to turf sites in 1984, and in 1985, triclopyr BEE was specifically registered for use on rangeland and permanent grass pastures. In 1995, the triclopyr TEA formulation received registration for use on rice crops to manage broadleaf weed species.[7]
Uses
As presented by the Wisconsin Department of Natural resources, triclopyr is a systemic herbicide and is believed selective in its control of dicotyledonous (broadleaf) weeds and woody plants,[6] while leaving monocotyledonous plants (such as grasses, bulbs, and conifers) largely unaffected.[4] The fact sheet from this Wisconsin agency goes on to state, "It is a WSSA [Weed Science Society of America] Group 4 herbicide, meaning that the mechanism of action is by mimicking the plant growth hormone auxin",[6] and that "[p]lant growth becomes abnormal and twisted following treatment, and plants decompose within one to two weeks after application".[6] The guidance goes on to state that
Triclopyr needs to be applied to plants that are actively growing. If there is flowing water at a treated site, higher concentrations or a repeated application may be required.[6]
Triclopyr is a widely used herbicide with active registrations in the United States, Brazil, Australia, Canada, Morocco, Paraguay, South Africa and Southeast Asia.[citation needed] In the United States, it is sold under the trade names Garlon, Remedy, Turflon, Weed-B-Gon, Brush-B-Gon, and RoundUp Brush Killer,[8] and in the United Kingdom as SBK Brushwood Killer.[citation needed] It is also a major ingredient in Confront.[citation needed] In addition to weed control, triclopyr has also been documented for use in controlling rust fungus on soybean crops.[5]
Environmental effects
Triclopyr, including its ester and amine salt forms, is rapidly converted to the triclopyr acid form in the environment. The acid form is largely water-soluble, while the ester form exhibits lower solubility. Triclopyr has a low vapor pressure, indicating a limited tendency to volatilize into the atmosphere. In aquatic environments, triclopyr degradation is accelerated by light, with a reported half-life of approximately 1 day under light conditions. Without light, it is more persistent in water, with a half-life of around 142 days.[9]
Triclopyr undergoes relatively rapid breakdown in soil, primarily through microbial activity. Soil half-lives typically range from 8 to 46 days, with longer persistence observed in deeper, less oxygenated soils. Although triclopyr is considered mobile in soil, studies have indicated limited movement below depths of 15 to 90 centimeters. Its movement in soil is influenced by factors such as organic matter content and rainfall. As a systemic herbicide, triclopyr is absorbed by plants through both leaves and roots and tends to accumulate in active growth regions. The rate of breakdown within plants varies widely depending on the species; reported half-lives in plants range from 3 to 24 days, with some plants like barley and wheat showing more rapid degradation.[9]
The compound is slightly toxic to ducks (LD50 = 1698mg/kg) and quail (LD50 = 3000mg/kg).[10] It has been found nontoxic to bees[9] and marginally toxic to fish (rainbow trout LC50 (96 hr) = 117 ppm).[11]
Garlon's fact sheet for a triclopyr ester—versus the triclopyr amine salt per se—indicates that further derivative to be highly toxic to fish, aquatic plants, and aquatic invertebrates, and so never used in waterways, wetlands, or other sensitive habitats.[12]
↑ PubChem Staff (10 July 2025). "PubChem Substance "Trichlopyr"[CompleteSynonym]". PubChem (chemical substances database entry). Bethesda, MD: National Institutes of Health, National Library of Medicine, National Center for Biotechnology Information (NIH NLM-NCBI).
1 2 3 4 ChEBI Staff (19 November 2014). "CHEBI:9682—trichlopyr". Chemical Entities of Biological Interest (ChEBI, database entry). Hinxton, Cambridgeshire, U.K.: European Molecular Biology Laboratory, European Bioinformatics Institute (EMBL-EBI). IUPAC Name [(3,5,6-trichloropyridin-2-yl)oxy]acetic acid.
1 2 3 4 5 Wisc. DNR Staff (December 2022). "Triclopyr Chemical Fact Sheet". DNR.WI.gov. Madison, WI: Wisconsin Department of Natural Resources (Wisc. DNR). Retrieved 10 July 2025. Triclopyr is a systemic herbicide (i.e., it moves throughout the plant tissue) that is believed to selectively act on broadleaf (dicot) and woody plants. It is a WSSA Group 4 herbicide, meaning that the mechanism of action is by mimicking the plant growth hormone auxin. Plant growth becomes abnormal and twisted following treatment, and plants decompose within one to two weeks after application. Triclopyr needs to be applied to plants that are actively growing.[bettersourceneeded]
↑ EPA Staff (October 1998). "R.E.D. Facts - Triclopyr"(PDF). Washington, DC: U.S. Environmental Protection Agency (EPA). Retrieved 28 March 2025.
↑ Daniel, Kyle (23 August 2024). "When Roundup Isn't Roundup". [Purdue] Landscape Report. No.24–11. Retrieved 23 April 2025.
1 2 3 Strid A, Hanson W, Cross A, Jenkins J (May 2018). "Triclopyr General Fact Sheet". National Pesticide Information Center. Oregon State University Extension Service. Retrieved 11 May 2025.
↑ Environmental Fate Of Triclopyr, Carissa Ganapathy, Environmental Monitoring & Pest Management Branch Department of Pesticide Regulation Sacramento, CA (dead link 23 October 2023)
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