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 pests. The group codes are intended for use on pesticide labels to help in the prevention and management of pesticide resistance in New Zealand. Information used in constructing these tables came from publicly available information from the Herbicide Resistance Action Committee and CropLife Australia.

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 C1 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, April 2017

* not registered or no longer registered in New Zealand

Group CodeMode of ActionChemical FamilyActive Ingredient
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
tralkoxydim*
Phenylpyrazoline "DEN" pinoxaden
B 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
Triazolopyrimidines

florasulam

flumetsulam
pyroxsulam

C1 Inhibition of photosynthesis at photosystem II Triazines ametryn*
atrazine
cyanazine
desmetryn*
prometryn
propazine
simazine
terbumeton*
terbuthylazine
terbutryn
Triazinones hexazinone
metamitron
metribuzin
Uracils bromacil
terbacil
Pyridazinones chloridazon
Phenyl-carbamates desmedipham
phenmedipham
C2 Inhibition of photosynthesis at photosystem II Ureas diuron
isoproturon
linuron
methabenzthiazuron
C3 Inhibition of photosynthesis at photosystem II Nitriles bromofenoxim*
bromoxynil
ioxynil
Benzothiadiazinone bentazone
Phenyl-pyridazines pyridate*
D Photosystem-I-electron diversion Bipyridyliums diquat
paraquat
E Inhibition of protoporphyrinogen oxidase (PPO) Diphenylethers oxyfluorfen
Oxadiazoles oxadiazon
Pyrimidinedione saflufenacil
Thiadiazole fluthiacet-methyl
Triazolinones carfentrazone-ethyl
sulfentrazone
F1 Bleaching: Inhibition of carotenoid biosynthesis at the phytoene desaturase step (PDS) Pyridazinones norflurazon*
Pyridinecarboxamides diflufenican
Others fluridone*
F2 Bleaching: Inhibition of 4-hydroxyphenylpyruvate-dioxygenase (4-HPPD) Triketones

mesotrione

topramezone

F3 Bleaching: Inhibition of carotenoid biosynthesis (unknown target) Triazoles amitrole
Isoxazolidinones clomazone
G Inhibition of EPSP synthase Glycines glyphosate
H Inhibition of glutamine synthetase Phosphinic acids glufosinate-ammonium
I Inhibition of DHP (dihydropteroate) synthase Carbamates asulam
K1 Microtubule assembly inhibition Dinitroanilines oryzalin
pendimethalin
trifluralin
Benzamides propyzamide
Benzenedicarboxylic acids chlorthal-dimethyl
K2 Inhibition of mitosis / microtubule organisation Carbamates chlorpropham
propham*
carbetamide*
K3 Inhibition of cell division Chloroacetamides acetochlor
alachlor
dimethenamid-P
s-metolachlor
propachlor
Oxyacetamides flufenacet
L Inhibition of cell wall (cellulose) synthesis Nitriles dichlobenil
N Inhibition of lipid synthesis - not ACCase inhibition Thiocarbamates EPTC*
triallate
Benzofuranes ethofumesate
Chloro-carbonic-acids TCA
flupropanate
2,2‑dichloropropionic acid
O1 Action like indole acetic acid (synthetic auxins) Phenoxy-carboxylic-acids

2,4-D
2,4-DB
dichlorprop-P
MCPA
MCPB
mecoprop

mecoprop-P

O2   Benzoic acids dicamba
O3   Pyridine carboxylic acids aminopyralid
clopyralid
fluroxypyr
picloram
triclopyr
O4   Arylpicolinate halauxifen-methyl
Z Unknown Arylaminopropionic acids flamprop-M-isopropyl
Organoarsenicals MSMA*
Other

benzalkonium chloride
chloropicrin
dazomet
endothal
fatty acids
metam sodium
methyl bromide
palm oil derived fatty acids

pine oil

gibberellic acid