Triclopyr
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| Names | |
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| Preferred IUPAC name
[(3,5,6-Trichloropyridin-2-yl)oxy]acetic acid | |
| Other names
3,5,6-TPA; Trident (Agriphar)
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| Identifiers | |
3D model (JSmol)
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| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.054.161 |
PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| C7H4Cl3NO3 | |
| Molar mass | 256.46 g·mol−1 |
| Appearance | Fluffy solid |
| Melting point | 148 to 150 °C (298 to 302 °F; 421 to 423 K) |
| 440 mg/L | |
| Solubility in acetone | 989 g/kg |
| Acidity (pKa) | 2.68 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Triclopyr (3,5,6-trichloro-2-pyridinyloxyacetic acid) is an organic compound in the pyridine group that is used as a systemic foliar herbicide[2] and fungicide.[3]
History
[edit]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.[4]
Uses
[edit]Triclopyr is a systemic herbicide and is selectively used to control dicotyledonous (broadleaf) weeds and woody plants while leaving monocotyledonous plants (such as grasses, bulbs, and conifers) largely unaffected.[2] It is classified as a WSSA (Weed Science Society of America) group 4 herbicide, indicating its mechanism of action involves mimicking the plant growth hormone auxin. This disruption leads to abnormal and twisted plant growth, ultimately causing the treated plants to die and then decompose within one to two weeks following application.[5]
Effective application of triclopyr requires that plants are actively growing. In situations where there is flowing water at a treatment site, higher concentrations or repeated applications of the herbicide may be necessary to achieve the desired control.[5]
In addition to weed control, triclopyr has also been documented for use in controlling rust fungus on soybean crops.[3]
In the USA, it is sold under the trade names Garlon, Remedy, Turflon, Weed-B-Gon (purple label), Brush-B-Gon, and RoundUp,[6] and in the United Kingdom as SBK Brushwood Killer. It is also a major ingredient in Confront. It is a widely used herbicide with active registrations in the USA, Brazil, Australia, Canada, Morocco, Paraguay, South Africa and Southeast Asia.
Environmental effects
[edit]Triclopyr, including its ester and 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.[7]
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.[7]
The compound is slightly toxic to ducks (LD50 = 1698 mg/kg) and quail (LD50 = 3000 mg/kg).[8] It has been found nontoxic to bees[7] and marginally toxic to fish (rainbow trout LC50 (96 hr) = 117 ppm).[9]
Garlon's fact sheet for their triclopyr ester product indicates that triclopyr is highly toxic to fish, aquatic plants, and aquatic invertebrates, and should never be used in waterways, wetlands, or other sensitive habitats.[10] This is only for the triclopyr ester product, not for the triclopyr amine product.
References
[edit]- ^ Merck Index, 11th Edition, 9572.
- ^ a b Appleby, Arnold P.; Müller, Franz; Carpy, Serge (2001). "Weed Control". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a28_165. ISBN 3-527-30673-0.
- ^ a b Shanmugasundaram, S.; Yeh, C.C.; Hartman, G.L.; Talekar, N.S. (1991). Vegetable Soybean Research Needs for Production and Quality Improvement (PDF). Taipei: Asian Vegetable Research and Development Center. pp. 86–87. ISBN 9789290580478. Archived from the original (PDF) on 6 February 2016. Retrieved 6 February 2016.
- ^ "R.E.D. Facts - Triclopyr" (PDF). United States Eviromental Protection Agency. October 1998. Retrieved 28 March 2025.
- ^ a b "Triclopyr Chemical Fact Sheet". Wisconsin Department of Natural Resources. December 2022. Retrieved 28 March 2025.
- ^ "When Roundup Isn't Roundup". 23 August 2024. Retrieved 23 April 2025.
- ^ a b c 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.
- ^ EXTOXNET (Extension Toxicology Network), Oregon State University
- ^ Environmental Fate Of Triclopyr, Carissa Ganapathy, Environmental Monitoring & Pest Management Branch Department of Pesticide Regulation Sacramento, CA (dead link 23 October 2023)
- ^ "Garlon XRT Herbicide" (PDF).