INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE
Three Herbicide Site of Action Classification Systems
In an ideal world we would only have one classification system for herbicide sites of action, no such luck. In 1990 whilst at the University of Manitoba I created a classification system based on numbers to assist growers in rotating herbicides, and published it in a fact sheet in 1991  – Group 1 = ACCase inhibitors, Group 2 = ALS inhibitors etc. This was added to and became the basis of the Canadian herbicide classification system, which in turn became the basis of the WSSA (Weed Science Society of America) herbicide classification system first published by Retzinger and Mallory-Smith in 1997.

In the early 1990's Australia created a classification system  based on letters, and HRAC (Herbicide-Resistance Action Committee) also created a classification system  also based on letters … unfortunately not the same letters as the Australian classification system. This was not done deliberately, each group worked independently and thought they were coming up with the “first classification system”. Because growers became use to “their” classification system it became impractical to choose just one system at a later date.

The WSSA classification system is only used in the USA and Canada. The Australian classification system is only used in Australia. The HRAC system is used in all other countries. The good news is that, on the whole, the systems map to each other, for example, HRAC Group O, Australian Group I, and WSSA Group 4 are synthetic auxins and contain the same list of herbicides. There are a few exceptions, particularly where the herbicide site of action is not well understood.

This website primarily uses the HRAC system because it is the classification system used in most countries. In the HRAC classification system there are 25 herbicide Groups. Group Z is unusual in that it represents herbicides with mechanisms that are not well understood. There are 4 Group Z’s. Although the sites of action of Group Z herbicides are not well know, we know that they fall into at least four groups that don’t act at the same site of action. So we have Z – Organoarsenicals, Z - Arylaminopropionic acids, Z – Pyrazoliums, and Z – Uknown.

Scroll down to see the herbicide groups sorted by the HRAC classification system but also listing the WSSA and Australian classifications. Please use the "Comment/Question/Report Error" button in the upper left if you see an error.

Ian Heap.

 
Cellular targets of herbicide action and herbicide classification by mode of action according to the Herbicide Resistance Action Committee (HRAC). Herbicides target only a few proteins or processes among the tremendous range present in plants.
From: Deciphering the evolution of herbicide resistance in weeds. Christophe Delye et. al. 2013, Trends in Genetics.

HRAC Group: : PSII inhibitors - Serine 264 Binders

Inhbition of Photosynthesis at PSll - Serine 264 Binders

Legacy HRAC Group : C1 Aussie Group : C

HRAC Group: : Inhibition of Very Long-Chain Fatty Acid Synthesis

Inhibition of lipid synthesis - not ACCase inhibition

Legacy HRAC Group : NC Aussie Group : NC

HRAC Group: 0 : Nucleic acid inhibitors

Unknown

Legacy HRAC Group : Z Aussie Group : Z

HRAC Group: 0 : Antimicrotubule mitotic disrupter

Unknown

Legacy HRAC Group : Z Aussie Group : Z

HRAC Group: 0 : Unknown

Unknown

Legacy HRAC Group : Z Aussie Group : Z

HRAC Group: 0 : Cell elongation inhibitors

Unknown

Legacy HRAC Group : Z Aussie Group : Z

HRAC Group: 1 : Inhibition of Acetyl CoA Carboxylase

Inhibition of Acetyl CoA Carboxylase

Legacy HRAC Group : A Aussie Group : A

HRAC Group: 10 : Inhibition of Glutamine Synthetase

Inhibition of Glutamine Synthetase

Legacy HRAC Group : H Aussie Group : N

HRAC Group: 12 : Phytoene Desaturase inhibitors

Inhibition of Phytoene Desaturase

Legacy HRAC Group : F1 Aussie Group : F

HRAC Group: 13 : Inhibition of Microtubule Assembly

Inhibition of Deoxy-D-Xyulose Phosphate Synthase

Legacy HRAC Group : F4 Aussie Group : Q

HRAC Group: 14 : Inhibition of Protoporphyrinogen Oxidase

Inhibition of Protoporphyrinogen Oxidase

Legacy HRAC Group : E Aussie Group : G

HRAC Group: 15 : Very Long-Chain Fatty Acid Synthesis inhibitors

Inhibition of Very Long-Chain Fatty Acid Synthesis

Legacy HRAC Group : K3 N Aussie Group : J, K

HRAC Group: 18 : Inhibition of Dihydropteroate Synthase

Inhibition of Dihydropteroate Synthase

Legacy HRAC Group : I Aussie Group : R

HRAC Group: 19 : Auxin Transport inhibitor

Inhibition of Auxin Transport

Legacy HRAC Group : P Aussie Group : P

HRAC Group: 2 : Inhibition of Acetolactate Synthase

Inhibition of Acetolactate Synthase

Legacy HRAC Group : B Aussie Group : B

HRAC Group: 22 : PS I Electron Diversion

PSI Electron Diversion

Legacy HRAC Group : D Aussie Group : L

HRAC Group: 23 : Inhibition of Microtubule Organization

Inhibition of Microtubule Organization

Legacy HRAC Group : K2 Aussie Group : E

HRAC Group: 24 : Uncouplers

Uncouplers

Legacy HRAC Group : M Aussie Group : Z

HRAC Group: 27 : Inhibition of Hydroxyphenyl Pyruvate Dioxygenase

Inhibition of Hydroxyphenyl Pyruvate Dioxygenase

Legacy HRAC Group : F2 Aussie Group : H

HRAC Group: 28 : Inhibition of dihydroorotate dehydrogenase (DHODH)

Inhibition of Dihydroorotate Dehydrogenase (DHODH)

Legacy HRAC Group : - Aussie Group : NC

HRAC Group: 29 : Inhibition of Cellulose Synthesis

Inhibition of Cellulose Synthesis

Legacy HRAC Group : L Aussie Group : I, O, Z

HRAC Group: 3 : Inhibition of Microtubule Assembly 2

Inhibition of Microtubule Assembly

Legacy HRAC Group : K1 Aussie Group : D

HRAC Group: 30 : Inhibition of Fatty Acid Thioesterase

Inhibition of Fatty Acid Thioesterase

Legacy HRAC Group : NC Aussie Group : NC

HRAC Group: 31 : Inhibition of Serine-Threonine Protein Phosphatase

Inhibition of Serine-Threonine Protein Phosphatase

Legacy HRAC Group : NC Aussie Group : NC

HRAC Group: 32 : Inhibition of Solanesyl Diphosphate Synthase

Inhibition of Solanesyl Diphosphate Synthase

Legacy HRAC Group : NC Aussie Group : NC

HRAC Group: 33 : Inhibition of Homogentisate Solanesyltransferase

Inhibition of Homogentisate Solanesyltransferase

Legacy HRAC Group : NC Aussie Group : NC

HRAC Group: 34 : Inhibition of Lycopene Cyclase

Inhibition of Lycopene Cyclase

Legacy HRAC Group : F3 Aussie Group : Q

HRAC Group: 4 : Auxin Mimics

Auxin Mimics

Legacy HRAC Group : O Aussie Group : I

HRAC Group: 5 : PSII inhibitors - Serine 264 Binders

Inhbition of Photosynthesis at PSll - Serine 264 Binders

Legacy HRAC Group : C1 C2 Aussie Group : C

HRAC Group: 6 : PSII inhibitors - Histidine 215 Binders

Inhbition of Photosynthesis at PSll - Histidine 215 Binders

Legacy HRAC Group : C3 Aussie Group : C

HRAC Group: 9 : Inhibition of Enolpyruvyl Shikimate Phosphate Synthase

Inhibition of EPSP synthase

Legacy HRAC Group : G Aussie Group : M

Site of Action Descriptions from WSSA

Amrhein, N. et al. 1980. Plant Physiol. 66:830.

Ashtakala, S. S. et al. 1989. J. Plant Physiol. 135:86.

Ashton, F. M. and A. S. Crafts. 1981. Mode of Action of Herbicides, 2nd ed. John Wiley & Sons, New York.

Barry and Pallett. 1990. Z. Naturforsch. 45c:492.

Bartels and Watson. 1978. Weed Sci. 26:198.

Burton, J.D. et al. 1989. Pestic. Biochem. Physiol. 34:76.

Casida, J. E. et al. 1974. Science 184:573.

Croteau, R. 1992. Plant Physiol. 98:1515.

Devine, M., S. O. Duke, and C. Fedtke. 1993. Physiology of Herbicide Action. Prentice Hall, New Jersey.

Dodge, A. D. 1982. Pages 57-77 in D. E. Moreland, J. B. St. John, and F. D. Hess, eds., Biochemical

Responses Induced by Herbicides. Am. Chem. Soc. Symp. Ser. No. 181, Washington D.C.

Duke and Hoagland. 1978. Plant Sci. Lett. 11:185.

Duke, S. O. et al. 1991. Weed Sci. 39:465.

Fedtke, C. 1982. Biochemistry and Physiology of Herbicide Action. Springer-Verlag, New York.

Focke and Lichtenthaler. 1987. Z. Naturforsch. 42c:1361.

Fuerst, E. P. 1987. Weed Technol. 1:270.

Gronwald, J. W. 1991. Weed Sci. 39:435.

Heim, D. R. et al. 1990. Plant Physiol. 93:695.

Heim and Larrinua. 1989. Plant Physiol. 91:1226.

Husted, R. F. et al. 1966. Proc. North Cent. Weed Control Conf. 44.

Böger P. et al. 2000. Pest. Managmt. Sci. 56:497-508.

Kidd, B. R. et al. 1982. Plant Sci. Lett. 26:211.

LaRossa and Schloss. 1984. J. Biol. Chem. 259:8753.

Lea, P.J. et al. 1984. Phytochemistry 23:1.

Lee and S.O. Duke. 1994. Abstr. Weed Sci. Soc. Am. 34:52.

Lee, T. T. 1980. Weed Res. 20:365.

Mallory-Smith, C.A. and E.J. Retzinger, Jr. 2003. Revised classification of herbicides by site of action for weed

resistance management strategies. Weed Technol. 17:605-619.

Myers, D. F. et al.2009. Indaziflam/BCS-AA10717-A new Herbicide for Pre-Emergent Control of Grasses and

Broadleaf Weeds for Turf and Ornamentals. WSSA Abstracts #386.

Sandmann and Böger. 1989. Pages 25-44 in P. Böger and G. Sandmann, eds., Target Sites of Herbicide

Action. CRC Press, Boca Raton, FL.

Sauer, H. et al. 1987. Z. Naturforsch. 42c:270.

Sterrett and Fretz. 1975. HortScience 10:161.

Stoltenberg, D.E. et al. 1989. Weed Sci. 37:512.

Tachibana, K. et al. 1986. J. Pestic. Sci. 11:33.

Vaughn and Lehnen. 1991. Weed Sci. 39:450.

Veerasekaran, P. et al. 1981. Pestic. Sci. 12:325.

 

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