Herbicide modes of action
The accompanying table lists herbicide active ingredients currently available for crop protection in New Zealand in groups according to shared risk from resistance development in target weeds. The group codes are intended for use on herbicide labels to help in the prevention and management of herbicide resistance in New Zealand. Information used in constructing these tables came from publicly available information from the Herbicide Resistance Action Committee and CropLife Australia.
Note that in May 2021, it was decided to move from a mode of action code system developed specifically for New Zealand based on the old HRAC system to a new code system that has recently been adopted not only by HRAC but all other countries in the world including USA and Australia. This will be phased in gradually over the next 3 years as labels get renewed on herbicide containers. In the interim, both systems will be shown in the table below.
The New Zealand Committee on Pesticide Resistance (NZCPR) is a subcommittee of the New Zealand Plant Protection Society (NZPPS). Neither NZCPR or NZPPS guarantees that the information in these tables is accurate or up-to-date, or accepts any liability for loss or damage arising from the use information contained in these tables.
Use of Group Codes on pesticide product labels
Pesticide product labels should include a statement about resistance prevention or management. This statement should begin with the mode of action group(s) of the active ingredient(s), as in the following example using atrazine:
Resistance prevention or management
Product_name contains the GROUP 5 herbicide, atrazine, and continuous use of herbicides in this group may lead to a build-up of weeds resistant to it. To prevent or delay resistance, alternate with a herbicide from another group if possible and adhere to label instructions. [More detailed resistance guidelines for this product could then follow if they exist from strategies on the NZPPS web-site]
Old Group Code | New Group Code | Mode of Action | Chemical Family | Active Ingredient |
---|---|---|---|---|
A | 1 | Inhibition of acetyl CoA carboxylase (ACCase) | Aryloxyphenoxypropionates "FOPs" | clodinafop-propargyl fenoxaprop-P-ethyl fluazifop-P-butyl haloxyfop-P quizalofop-P-ethyl |
Cyclohexanediones "DIMs" | clethodim sethoxydim* tepraloxydim tralkoxydim* |
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Phenylpyrazoline "DEN" | pinoxaden | |||
B | 2 | Inhibition of acetolactate synthase ALS (acetohydroxyacid synthase AHAS) | Sulfonylureas | chlorimuron-ethyl chlorsulfuron flazasulfuron foramsulfuron* halosulfuron-methyl iodosulfuron mesosulfuron-methyl metsulfuron-methyl nicosulfuron primisulfuron-methyl thifensulfuron-methyl tribenuron-methyl |
Imidazolinones | imazapyr imazethapyr |
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Triazolopyrimidines |
florasulam flumetsulam |
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C1 | 5 | Inhibition of photosynthesis at photosystem II | Triazines | ametryn* atrazine cyanazine desmetryn* prometryn propazine simazine terbumeton* terbuthylazine terbutryn |
Triazinones | hexazinone metamitron metribuzin |
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Uracils | bromacil terbacil |
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Pyridazinones | chloridazon | |||
Phenyl-carbamates | desmedipham phenmedipham |
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C2 | 5 | Inhibition of photosynthesis at photosystem II | Ureas | diuron isoproturon linuron methabenzthiazuron |
C3 | 6 | Inhibition of photosynthesis at photosystem II | Nitriles | bromofenoxim* bromoxynil ioxynil |
Benzothiadiazinone | bentazone | |||
Phenyl-pyridazines | pyridate* | |||
D | 22 | Photosystem-I-electron diversion | Pyridiniums | diquat paraquat |
E | 14 | Inhibition of protoporphyrinogen oxidase (PPO) | Diphenyl ether | oxyfluorfen |
N-phenyl-imide |
flumioxazin fluthiacet-methyl saflufenacil |
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N-phenyl-oxadiazolone | oxadiazon | |||
N-phenyl-triazolinone | carfentrazone-ethyl sulfentrazone |
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F1 | 12 | Bleaching: Inhibition of carotenoid biosynthesis at the phytoene desaturase step (PDS) | N-phenyl heterocycle | norflurazon* |
Pyridinecarboxamides | diflufenican | |||
Diphenyl heterocycle | fluridone* | |||
F2 | 27 | Bleaching: Inhibition of 4-hydroxyphenylpyruvate-dioxygenase (4-HPPD) | Pyrazoles |
mesotrione topramezone |
F3 | 34 | Bleaching: Inhibition of carotenoid biosynthesis (unknown target) | Triazoles | amitrole |
13 | Isoxazolidinones | clomazone | ||
G | 9 | Inhibition of EPSP synthase | Glycines | glyphosate |
H | 10 | Inhibition of glutamine synthetase | Phosphinic acids | glufosinate-ammonium |
I | 18 | Inhibition of DHP (dihydropteroate) synthase | Carbamates | asulam |
K1 | 3 | Microtubule assembly inhibition | Dinitroanilines |
oryzalin prodiamine |
Benzamide | propyzamide | |||
Benzoic acid | chlorthal-dimethyl | |||
K2 | 23 | Inhibition of mitosis / microtubule organisation | Carbamates | chlorpropham propham* carbetamide* |
K3 | 15 | Inhibition of cell division | Alpha-chloroacetamides | acetochlor alachlor dimethenamid-P s-metolachlor propachlor |
Isoxazoline | pyroxasulfone | |||
Alpha-oxyacetamides | flufenacet | |||
L | 29 | Inhibition of cellulose biosynthesis | Alkylazines | indaziflam |
Nitriles | dichlobenil | |||
N | 15 | Inhibition of lipid synthesis - not ACCase inhibition | Thiocarbamates | prosulfocarb triallate |
15 | Benzofuran | ethofumesate | ||
0 | Chloro-carbonic-acids | TCA flupropanate 2,2‑dichloropropionic acid |
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O1 | 4 | Action like indole acetic acid (auxin mimics) | Phenoxy-carboxylic-acids |
2,4-D mecoprop-P |
O2 | 4 | Benzoate | dicamba | |
O3/4 | 4 | Pyridine carboxylates | aminopyralid clopyralid halauxifen-methyl picloram |
|
O3/4 | 4 | Pyridyloxy-carboxylates |
fluroxypyr triclopyr |
|
4 |
aminocyclopyrachlor |
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31 | Inhibitor of serine threonine protein phosphatase | Unknown subgroup |
endothal |
|
Z | 0 | Unknown | Arylaminopropionic acids | flamprop-M-isopropyl |
Organoarsenicals | MSMA* | |||
Other |
fatty acids pine oil |