Chemistry:Flufenacet

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Flufenacet is an oxyacetanilide herbicide applied before crops have emerged.[1] It was registered for use in the United States in 1998 and the European Union in 2004.[2]

Mode of action

Flufenacet is related to the chloroacetamide class of herbicides and has the same mode of action through inhibiting the germination of seeds by inhibiting very long chain fatty acid synthesis.[3][4]

In the model plant Arabidopsis thaliana it causes similar symptoms to the fiddlehead mutant.[5]

Usage

Flufenacet usage in England

In temperate Europe, flufenacet is commonly used in cereal crops to control grass weeds such as black-grass (Alopecurus myosuroides) that have evolved resistance to other herbicides and is applied in combination with other herbicides including pendimethalin, diflufenican, flurtamone, metribuzin and aclonifen.[6] As of 2019 in the United Kingdom, resistance to flufenacet had begun to be found in black-grass and rye-grass.[7] As of 2022 it was the most widely applied herbicide and third most widely applied pesticide in England, being used on 2.9 million hectares.[8]

Environmental fate

Map of the estimated use of the herbicide flufenacet in the United States in 2018 and graph showing annual use since 1992

Flufenacet and its metabolites can be classified as PFAS substances, or so-called "forever chemicals". They break down to produce trifluoroacetic acid (TFA), a persistent substance that pollutes groundwater.[9][10]

Toxicity

In September 2024, the European Food Safety Authority has concluded that flufenacet is an endocrine disruptor of humans and wild mammals via the thyroid (T)-modality.[9] The active substance falls under the exclusion criteria of the Plant Protection Products Regulation. Re-authorisation of the active substance by the EU Commission is therefore no longer possible. The EU Commission will draw up a proposal for the non-authorisation of flufenacet, including withdrawal and sunset periods, which the EU member states are expected to vote on in spring 2025.[11][12] In March 2025, the EU agreed to ban flufenacet, effective from June 2025, but with the option for individual states to allow use for a further year.[13]

Synthesis

Flufenacet can be obtained by reacting equivalent amounts of 2-methylsulfonyl-5-trifluoromethyl-1,3,4-thiadiazole with 2-hydroxy[N-(4-fluoropheny)-N-isopropyl]acetamide in the presence of sodium hydroxide in acetone.[14]

Synthesis
Synthesis

References

  1. ↑ Rouchaud, J.; Neus, O.; Eelen, H.; Bulcke, R. (2001). "Persistence, Mobility, and Adsorption of the Herbicide Flufenacet in the Soil of Winter Wheat Crops". Bulletin of Environmental Contamination and Toxicology 67 (4): 609–616. doi:10.1007/s001280167. PMID 11779079. Bibcode: 2001BuECT..67..609R. 
  2. ↑ "Flufenacet (Ref: FOE 5043)". University of Hertfordshire. http://sitem.herts.ac.uk/aeru/ppdb/en/Reports/331.htm. 
  3. ↑ "Chloroacetamide Mode of Action, I: Inhibition of Very Long Chain Fatty Acid Synthesis in Scenedesmus acutus". Zeitschrift für Naturforschung C 53 (11–12): 995–1003. 1 December 1998. doi:10.1515/znc-1998-11-1210. 
  4. ↑ Matthes, Bernd; Schmalfuß, Jochen; Böger, Peter (1 December 1998). "Chloroacetamide Mode of Action, II: Inhibition of Very Long Chain Fatty Acid Synthesis in Higher Plants". Zeitschrift für Naturforschung C 53 (11–12): 1004–1011. doi:10.1515/znc-1998-11-1211. 
  5. ↑ Lechelt-Kunze, C.; Meissner, R. C.; Drewes, M.; Tietjen, K. (2003). "Flufenacet herbicide treatment phenocopies the fiddlehead mutant in Arabidopsis thaliana". Pest Management Science 59 (8): 847–856. doi:10.1002/ps.714. PMID 12916765. Bibcode: 2003PMSci..59..847L. 
  6. ↑ Dücker, Rebecka; Zöllner, Peter; Parcharidou, Evlampia; Ries, Susanne; Lorentz, Lothar; Beffa, Roland (November 2019). "Enhanced metabolism causes reduced flufenacet sensitivity in black-grass (Alopecurus myosuroides Huds.) field populations". Pest Management Science 75 (11): 2996–3004. doi:10.1002/ps.5414. PMID 30891919. Bibcode: 2019PMSci..75.2996D. 
  7. ↑ Impey, Louise (12 July 2019). "How to get effective weed control when using flufenacet". Farmers Weekly. https://www.fwi.co.uk/arable/crop-management/weed-management/how-to-get-effective-weed-control-when-using-flufenacet. 
  8. ↑ "PESTICIDE USAGE SURVEY REPORT 309". FERA. https://pusstats.fera.co.uk/api/report-download/699. 
  9. ↑ 9.0 9.1 Arp, Hans Peter H.; Gredelj, Andrea; Glüge, Juliane; Scheringer, Martin; Cousins, Ian T. (12 November 2024). "The Global Threat from the Irreversible Accumulation of Trifluoroacetic Acid (TFA)". Environmental Science & Technology 58 (45): 19925–19935. doi:10.1021/acs.est.4c06189. PMID 39475534. Bibcode: 2024EnST...5819925A. 
  10. ↑ European Food Safety Authority (September 2024). "Peer review of the pesticide risk assessment of the active substance flufenacet". EFSA Journal 22 (9). doi:10.2903/j.efsa.2024.8997. PMID 39345971. 
  11. ↑ Bockholt, Karl (2024-10-02). "Schlag ins Kontor: Behörde streicht wichtigen Wirkstoff gegen Unkraut" (in de). https://www.agrarheute.com/pflanze/getreide/schlag-ins-kontor-behoerde-streicht-wichtigen-wirkstoff-gegen-unkraut-626748. 
  12. ↑ "Pflanzenschutz. Es ist soweit: auch Flufenacet fällt weg" (in de). 2024-09-27. https://www.dlg-mitteilungen.de/artikel/pflanzenschutz-es-ist-soweit-auch-flufenacet-faellt-weg. 
  13. ↑ Birch, Rachel (25 March 2025). "EU agrees to ban herbicide flufenacet due to its toxicity". Agriland.ie. https://www.agriland.ie/farming-news/eu-agrees-to-ban-herbicide-flufenacet-due-to-its-toxicity/. 
  14. ↑ Hatzios KK, ed; Herbicide Handbook of the Weed Science Society of America. 7th ed. Suppl. Champaign, IL: Weed Sci Soc Amer, S. 9 (1998).
  • Flufenacet in the Pesticide Properties DataBase (PPDB)



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