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]
Herbicide Mode of Action Groups, November 2023
*no longer available in New Zealand
| New Group Code | Old Group Code | Mode of Action | Chemical Family | Active Ingredient |
| 1 | A | 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* | ||||
| Phenylpyrazoline "DEN" | pinoxaden | |||
| 2 | B | Inhibition of acetolactate synthase (ALS) | Sulfonylureas | chlorimuron-ethyl |
| chlorsulfuron | ||||
| flazasulfuron | ||||
| foramsulfuron | ||||
| halosulfuron-methyl | ||||
| iodosulfuron | ||||
| mesosulfuron-methyl | ||||
| metsulfuron-methyl | ||||
| nicosulfuron | ||||
| primisulfuron-methyl | ||||
| thifensulfuron-methyl | ||||
| tribenuron-methyl | ||||
| triflusulfuron-methyl | ||||
| Imidazolinones | imazapyr | |||
| imazethapyr | ||||
| Triazolinone | thiencarbazone-methyl | |||
| Triazolopyrimidines | florasulam | |||
| flumetsulam | ||||
| pyroxsulam | ||||
| 3 | K1 | Microtubule assembly inhibition | Dinitroanilines | oryzalin |
| pendimethalin | ||||
| prodiamine | ||||
| trifluralin | ||||
| Benzamide | propyzamide | |||
| Benzoic acid | chlorthal-dimethyl | |||
| 4 | O1 | Auxin mimics | Phenoxy-carboxylates | 2,4-D |
| 2,4-DB | ||||
| dichlorprop* | ||||
| MCPA | ||||
| MCPB | ||||
| mecoprop | ||||
| O2 | Benzoate | dicamba | ||
| O3/4 | Pyridine-carboxylates | aminopyralid | ||
| clopyralid | ||||
| halauxifen | ||||
| picloram | ||||
| O3/4 | Pyridyloxy-carboxylates | fluroxypyr | ||
| triclopyr | ||||
| Pyrimidine-carboxylates | aminocyclopyrachlor | |||
| 5 | C1 | Inhibition of photosynthesis at photosystem II (serine 264 binders) | Triazines | atrazine |
| cyanazine | ||||
| prometryn | ||||
| propazine | ||||
| simazine | ||||
| terbuthylazine | ||||
| terbutryn | ||||
| Triazinones | hexazinone | |||
| metamitron | ||||
| metribuzin | ||||
| Uracils | bromacil | |||
| terbacil | ||||
| Pyridazinones | chloridazon | |||
| Phenyl-carbamates | desmedipham | |||
| phenmedipham | ||||
| C2 | Ureas | diuron | ||
| isoproturon | ||||
| linuron | ||||
| methabenzthiazuron | ||||
| metobromuron | ||||
| 6 | C3 | Inhibition of photosynthesis at photosystem II (histidine 215 binders) | Nitriles | bromoxynil |
| ioxynil | ||||
| Benzothiadiazinone | bentazone | |||
| Phenyl-pyridazine | pyridate* | |||
| 9 | G | Inhibition of EPSP synthase | Glycine | glyphosate |
| 10 | H | Inhibition of glutamine synthetase | Phosphinic acid | glufosinate-ammonium |
| 12 | F1 | Inhibition of phytoene desaturase | N-phenyl heterocycle | norflurazon* |
| Phenyl ether | diflufenican | |||
| 13 | F3 | Inhibition of deoxy-D-xylulose phosphate synthase | Isoxazolidinone | clomazone |
| 14 | E | Inhibition of protoporphyrinogen oxidase (PPO) | Diphenyl ether | oxyfluorfen |
| N-phenyl-imide | flumioxazin | |||
| fluthiacet-methyl | ||||
| saflufenacil | ||||
| N-phenyl-oxadiazolone | oxadiazon | |||
| N-phenyl-triazolinone | carfentrazone-ethyl | |||
| sulfentrazone | ||||
| 15 | K3 | Inhibition of very long-chain fatty acid synthesis | Alpha-chloroacetamides | acetochlor |
| alachlor | ||||
| dimethenamid | ||||
| metolachlor | ||||
| propachlor | ||||
| Isoxazoline | pyroxasulfone | |||
| Alpha-oxyacetamide | flufenacet | |||
| N | Thiocarbamates | prosulfocarb | ||
| triallate | ||||
| Benzofuran | ethofumesate | |||
| 18 | I | Inhibition of DHP (dihydropteroate) synthase | Carbamate | asulam |
| 22 | D | Photosystem-I electron diversion | Pyridiniums | diquat |
| paraquat | ||||
| 23 | K2 | Inhibition of mitosis / microtubule organisation | Carbamates | chlorpropham |
| propham | ||||
| 27 | F2 | Inhibition of 4-hydroxyphenylpyruvate-dioxygenase (4-HPPD) | Pyrazoles | mesotrione |
| topramezone | ||||
| 29 | L | Inhibition of cellulose biosynthesis | Alkylazine | indaziflam |
| Nitrile | dichlobenil* | |||
| 31 | Inhibitor of serine threonine protein phosphatase | Unknown subgroup | endothal | |
| 34 | F3 | Inhibition of lycopene cyclase | Triazole | amitrole |
| 0 | N | Unknown | Chloro-carbonic-acids | TCA* |
| flupropanate | ||||
| 2,2‑DPA (dalapon)* | ||||
| Z | Arylaminopropionic acids | flamprop-M-isopropyl | ||
| Other | fatty acids | |||
| nonanoic acid | ||||
| palm oil fatty acids | ||||
| pine oil |
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