Phenoxy herbicide

Source: Wikipedia, the free encyclopedia.
(Redirected from
Phenoxy acid
)
Phenoxyacetic acid, the partial structure which many of these herbicides have in common

Phenoxy herbicides (or "phenoxies") are two families of chemicals that have been developed as commercially important herbicides, widely used in agriculture. They share the part structure of phenoxyacetic acid.

Auxins

The first group to be discovered act by mimicking the auxin growth hormone

monocotyledonous crops such as wheat or maize
(corn), they selectively kill broad-leaf weeds, leaving the crops relatively unaffected.

  • IAA
    IAA
  • MCPA
    MCPA
  • 2,4-D
    2,4-D
  • 2,4,5-T
    2,4,5-T

Introduced in 1946, these

chiral centre in these molecules and biological activity is found only in the (2R)-isomer (illustrated for dichlorprop).[3]

  • Mecoprop
    Mecoprop
  • (2R)-Dichlorprop
    (2R)-Dichlorprop
  • Fenoprop
    Fenoprop
  • 2,4-DB
    2,4-DB
  • MCPB
    MCPB

Other members of this group include 4-(2,4-dichlorophenoxy)butyric acid (

esters
since these are also capable of producing the parent acid in situ.

US Geological Survey estimate of 2,4-D use in the USA to 2019

The use of herbicides in US agriculture is mapped by the US Geological Survey. As of 2019, 2,4-D was the most used of the auxins. 45,000,000 pounds (20,000,000 kg) were sprayed that year,

genetically modified to be resistant to it have been cultivated.[8]

ACCase inhibitors

In the 1970s, agrochemical companies were working to develop new herbicides to be complementary to the auxins. The aim was to find materials which would selectively control grass weeds in broad-leaf crops such as cotton and soybean.

Cyhalofop: X=CH, R1=CN, R2=F
Diclofop: X=CH, R1=R2=Cl
Chlorazifop: X=N, R1=R2=Cl
Fluazifop: X=N, R1=CF3, R2=H
Haloxyfop: X=N, R1=CF3, R2=Cl

In 1973,

brand name Fusilade while Dow marketed haloxyfop as its methyl ester.[9]
All these compounds have an additional oxygen-linked
phenyl ring with its OCH(CH3)COOH group and as a class are called "fops", referring to their common fenoxy-phenoxy [sic] feature.[10]

This group of herbicides acts by inhibiting plant

stereoisomer
which binds to plant ACCase, just as that isomer is responsible for the activity of dichlorprop as an auxin.

Fenoxaprop-P-ethyl
US Geological Survey estimate of fluazifop use in the USA to 2018

Salts and esters of this class of herbicide are active owing to their ability to metabolise to the corresponding parent acid. For example, fenoxaprop-P ethyl

enantiomers
.

Resistance

Cummins et al., 1999, 2009, and 2013 find that

resistance reduces hydrogen peroxide concentrations at the application site, while the wild type responds with an increase.[20]

References

  1. PMID 19823992
    .
  2. S2CID 85637273
    .
  3. ISBN 978-0-08-095168-3
    .
  4. ISBN 9780120007547
    .
  5. ^ US Geological Survey (2021-10-12). "Estimated Agricultural Use for 2,4-D, 2019". Retrieved 2021-12-27.
  6. ^ US Geological Survey (2021-10-12). "Estimated Agricultural Use for MCPA, 2018". Retrieved 2021-12-27.
  7. ^ US Geological Survey (2021-10-12). "Estimated Agricultural Use for Dicamba, 2019". Retrieved 2021-12-27.
  8. ^ Gray, Bryce (2016-11-09). "EPA approves Monsanto's less-volatile form of dicamba herbicide". St. Louis Post-Dispatch. Retrieved 2021-12-27.
  9. ^ a b Evans, D. (1992). "Designing more efficient herbicides" (PDF). Proceeding of the First International Weed Control Congress , Melbourne. pp. 37–38. Retrieved 2021-02-27.
  10. ^ "Aryloxyphenoxypropionic herbicides". BCPC. Retrieved 2022-10-06.
  11. PMID 2902848
    .
  12. S2CID 27124700
    .
  13. PMID 12859251
    .
  14. ISBN 9783527339471
    .
  15. ^ Pesticide Properties Database. "Fenoxaprop-P-ethyl". University of Hertfordshire. Retrieved 2021-03-02.
  16. ^ Pesticide Properties Database. "Quizalofop-P-ethyl". University of Hertfordshire. Retrieved 2021-03-02.
  17. ^ Pesticide Properties Database. "Cyhalofop-butyl". University of Hertfordshire. Retrieved 2022-10-06.
  18. ^ Pesticide Properties Database. "Fluazifop-P-butyl". University of Hertfordshire. Retrieved 2021-03-02.
  19. ^ US Geological Survey (2021-10-12). "Estimated Agricultural Use for Fluazifop, 2018". Retrieved 2021-12-27.
  20. S2CID 246978319
    .
Retrieved from "https://en.wikipedia.org/w/index.php?title=Phenoxy_herbicide&oldid=1220218794"