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The Herbicide Resistance Action Committee (HRAC) classifies herbicides by their mode of action (MoA) to provide a uniform way for farmers and growers to identify the agents they use and better manage pesticide resistance around the world.[1][2] It is run by CropLife International[3] in conjunction with the Weed Science Society of America (WSSA).[4]

Resistance overview

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A weed that develops resistance to one herbicide typically has cross-resistance to other herbicides with the same mode of action (MoA), so herbicides with different MoAs, or different resistance groups, are needed. Preventative weed resistance management rotates herbicide types to prevent selective breeding of resistance to the same mode of action. By rotating MoAs, successive generations gain no advantage from any resistant mutations of the last generation.[5] Cross-resistant and multiply resistant weeds resist multiple MoAs,[6] and are particularly difficult to control.

Naming types

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The HRAC give a letter based class to each active constituent herbicide. The Australian HRAC code is separately assigned, though is often the same as the global code. In 2021, alternative numeric classes were added, to make codes globally more consistent. This set of classification changes also added or moved a few herbicides that had been misclassified, and reduced regional concerns that using the English alphabet could be an impediment for international growers.[5]

Herbicides that act through multiple modes have multiple classifications, corresponding to each MoA.[7] For example, Quinmerac is classified as Group 4/29 (O/L) because it is both an Auxin mimic (Group 4 or O) and inhibits cellulose synthesis (Group 29 or L).[8]

Groups

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HRAC Classification Groups[9][8]
HRAC (AUS) HRAC (Global) HRAC (Numeric) Mode of action Example herbicides Example chemical families
A A 1 Inhibits acetyl coa carboxylase Haloxyfop-methyl, Clethodim, Sethoxydim, Pinoxaden Aryloxyphenoxy-propionates, Cyclohexanediones, Phenylpyrazolines
B B 2 Inhibits acetolactate synthase Imazamox, Chlorsulfuron, Pyrithiobac-sodium, Florasulam Imidazolinones, Pyrimidinyl benzoates, Sulfonylureas, Triazolopyrimidines
C C1 / C2 5 Inhibits photosynthesis at PSII - serine 264 binders Atrazine, Simazine, Propanil, Amicarbazone, Bromacil, Diuron Triazines, Amides, Phenlcarbamates, Pyridazinones, Triazinones, Triazolinones, Uracil, Ureas
C C3 6 Inhibits photosynthesis at PSII - histidine 215 binders/uncouplers Bentazon, Bromoxynil, Ioxynil Benzothiadiazinones, Nitriles
- C2 7 Isoproturon[10] Urea
D K1 3 inhibits microtubule assembly Trifluralin, Pendimethalin, Propyzamide, Dithiopyr[9], butamiphos, chlorthal-dimethyl[11] Dinitroanilines, Benzoic acids, Pyridines,[9] Phosphoroamidates, Benzoic acids[11]
E K2 23 Inhibits microtubule organisation Carbetamide Carbamates
F F1 12 Inhibits phytoene desaturase Diflufenican, Norflurazon Phenyl ethers, N-Phenyl heterocycles
G E 14 Inhibits protoporphyrinogen oxidase Butafenacil, Carfentrazone-ethyl, Oxyfluorfen N-Phenyl-imides. Diphenyl ethers, N-Phenyl-oxadiazolones, Phenylpyrazoles
H F2 27 Inhibits hydroxyphenyl pyruvate dioxygenase Isoxaflutole, Pyrasulfotole, Mesotrione Ssoxazoles, Pyrazoles, Triketones
I O 4 Auxin mimic Dicamba, Halauxifen, Picloram, 2,4-D, MCPA, Triclopyr, Quinclorac 6-Arylpicolinates, 6-Chloropicolinates, Benzoates, Phenoxy-carboxylates, Pyridyloxy-carboxylates, Quinoline-carboxylates
J K3 / N 15 Inhibits very long chain fatty acid synthesis Prosulfocarb, Ethofumesate Thiocarbamates, Benzofurans
J - Unknown Bensulide, Delapon Chlorocarbonic acids
K K3 15 Inhibits very long chain fatty acid synthesis Metolachlor, Pyroxasulfone α-Chloroacetamides, Isoxazolines
K - Unknown Napropamide Acetamide
L D 22 PS I electron diversion Diquat, Paraquat Pyridinium
M G 9 Inhibits enolpyruvil shikimate phosphate synthase Glyphosate Glycine
N H 10 Inhibits glutamine-synthetase Glufosinate-ammonium Phosphinic acid
O L 29 inhibition of cellulose synthesis Isoxaben, Dichlobenil, Indaziflam Nitrile, Benzamide, Alkylazine
P P 19 Auxin transport inhibitor Naptalam Aryl-carboxylates
Q F3 / F4 13 Inhibits deoxy-d-xylulose phosphate synthesis Clomazone, Bixlozone Isoxazolidinone
Q - - Unknown Amitrole Triazole
R I 18 Inhibits dihydropteroate synthase Asulam carbamate
- - 28 Inhibition of dihydroorotate dehydrogenase Tetflupyrolimet
T Q / Z 30 Inhibits fatty acid thioesterase Cynmethylin Benzyl-ether
Z R 31 Inhibits serine-threonine protein phosphatase Endothal Other
Z Z - Unknown Flamprop-m, DSMA, MSMA, Pelargonic acid Arylaminopropionic acid, Others
- M 24 Uncouplers Dinosam Dinitrophenol
- S / F3 32 Inhibition of Solanesyl Diphosphate Synthase Aclonifen Diphenyl ether
- T 33 Inhibition of Homogentisate Solanesyltransferase Cyclopyrimorate Phenoxypyridazine

References

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  1. ^ "Appendix 7. Classification of Herbicides According to Mode of Action" (PDF). University of Florida IFAS Extension. Retrieved November 20, 2024.
  2. ^ "HRAC MoA Classification Update Webinar Training 6th May 2022". European Weed Research Society. Retrieved November 20, 2024.
  3. ^ Sievernich, Bernd; Belvaux, Xavier; Hunt, Barrie (February 2024). "HRAC Europe – Partner on Weed Resistance Management". Julius-Kühn-Archiv. 478 (31). Bundesbehörden Und Einrichtungen Im Geschäftsbereich Des Bundesministeriums Für Ernährung Und Landwirtschaft (BMEL): 94. doi:10.5073/20240109-073031-0.
  4. ^ Hirai, Kenji; Uchida, Atsushi; Ohno, Ryuta (2002), Böger, Peter; Wakabayashi, Ko; Hirai, Kenji (eds.), "Major Synthetic Routes for Modern Herbicide Classes and Agrochemical Characteristics", Herbicide Classes in Development, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 179–289, doi:10.1007/978-3-642-59416-8_10, ISBN 978-3-642-63972-2, retrieved 2024-11-21
  5. ^ a b "Fact sheet HRAC Mode of Action Updates" (PDF). Weed Science Society of America. Retrieved 20 September 2024.
  6. ^ "Overview". Herbicide Resistance Action Committee. Retrieved 20 September 2024.
  7. ^ Oršolić, Davor; Pehar, Vesna; Šmuc, Tomislav; Stepanić, Višnja (2021-06-01). "Comprehensive machine learning based study of the chemical space of herbicides". Scientific Reports. 11 (1): 11479. doi:10.1038/s41598-021-90690-w. ISSN 2045-2322. PMC 8169684. PMID 34075109.
  8. ^ a b "2024 HRAC GLOBAL HERBICIDE MOA CLASSIFICATION MASTER LIST". Herbicide Resistance Action Committee.
  9. ^ a b c "Australia Herbicide Classification Lookup". Herbicide Resistance Action Committee. Retrieved 20 September 2024.
  10. ^ "Pesticide Properties Database". sitem.herts.ac.uk.
  11. ^ a b "2008 Herbicide Mode of Action Table". weedscience.org.
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