Herbicide Resistance – Prairie Crop Protection

Weed Resistance to Herbicides

In recent years, the number of herbicide-resistant weeds and the areas they infest have increased.

Most herbicide-resistant weed infestations have developed following repeated use of the same herbicide (or herbicide group) for a number of years on the same field. Growers who have developed weed resistance on their farms will typically see a weed, which is normally controlled by a herbicide, escape uncontrolled after a number of years of use of the same product or product group. Individual plants may be resistant to 1.5 up to 10 or more times the normal field rate.

Herbicide Groups

To help you plan your herbicide program, the following table lists “herbicide groups.” To slow down the process of developing weed resistance, tank mix products from different groups to control the same key weeds and/or use products from different groups from year to year on your fields. ‘Herbicide Layering’ is another way to use multiple herbicide groups that control of the same weed for managing herbicide resistance. Layering involves application of a soil active herbicide followed by in-crop foliar sprays. The soil applied herbicide provides a base for control and the foliar herbicide picks up any stragglers. Soil applied herbicides also help to control certain difficult to control weeds as well as improving crop yields by removal of weeds in the crop’s sensitive early growth stage.

Table 8. Herbicide Site of Action and Chemical Family for Resistant Weed Management

Site of Action (Group)	Common Name	Herbicide Tradename	Premix or Co-pack^†Tradenames*
ACC-ase Inhibitor (1) Aryloxyphenoxy propionic acid“Fop”	clodinafop	Horizon NG=Foothills NG, Cadillac One=Ladder All In, MPOWER Aurora= Cadillac=Foax=Ladder 240 EC= Signal=Slam’-R	Signal FSU^†, Traxos, TraxosTwo^†
fenoxaprop	Puma Advance, Bengal WB=Cordon=MPower HellCat=Vigil WB	Tundra
quizalofop	Assure II=Yuma GL=Contender=MPOWER Quiz	MPOWER Boa IQ*^†
Cyclohexanedione “Dim”	clethodim	Select=Centurion=Antler=Arrow=Clethodim 250= MPower Independence=Shadow RTM= Patron 240 EC=Statue, Arrow-All-In	MPower Ninja Master*^†
sethoxydim	Poast Ultra	Odyssey Ultra/Odyssey Ultra NXT^†, Solo Ultra^†
tralkoxydim	Achieve=Bison=Marengo=Nufarm Tralkoxydim	–
Phenylpyrazolin “Den”	pinoxaden	Axial, Brazen	Avenza^†, Axial iPak^†, Axial Xtreme,* Axial Xtreme iPak^†, BroadBand, Rezuvant^†, Traxos, TraxosTwo^†
ALS Enzyme Inhibitor (2) Imidazolinone“Imi”	imazamethabenz	Assert 300 SC	–
imazamox	Solo WDG/Solo ADV, Mizuna, Davai 80SL, Amity WDG	Altitude FX2/FX3, Ares SN, Odyssey=Duet=MPower Ninja, MPOWER Ninja Master^†, Odyssey NXT, Odyssey Ultra/Odyssey Ultra NXT^†, Salute^†, Solo Ultra^†, Viper ADV*
imazapyr	–	Ares SN, Salute*^†
imazethapyr	Pursuit 240= Guardsman Gladiator= MPower Kamikaze=Phantom	MPOWER Ninja Master^†, Odyssey=Duet= MPower Ninja, Odyssey NXT,* Odyssey Ultra/Odyssey Ultra NXT*^†
Sulfonylurea “SU”	ethametsulfuron	Muster Toss-N-Go	–
foramsulfuron	Option 2.25 OD	–
halosulfuron	Permit WG	–
metsulfuron	Ally, Escort	Express Pro, MPower X-Pro^†, Navius/Navius Flex, Reclaim^†, Reclaim II^†, Travallas
nicosulfuron	Accent=Nicosh	Ultim 75DF/Grande
rimsulfuron	Prism, Sortan IS	Ultim 75DF/Grande
thifensulfuron	Pinnacle	Barricade II^†= MPower Foxxy R^†, Broadside^†=Refine M^†, Enforcer MSU^†, MPOWER Foxxy CRX, Predicade^†, Refine SG=Nimble=Deploy=MPower RX, Retain SG^†, Signal FSU^†, Travallas, Triton C, Triton K*^†
tribenuron	Express SG=Spike=MPower Extra=Inferno WDG	Barricade II^†=MPower Foxxy R^†, Broadside^†=Refine M^†, Express FX^†, Express Pro, Enforcer MSU^†, Inferno Duo, Intruvix^†, Luxxur^†, MPOWER Foxxy CRX^†, MPower X-Pro^†, Predicade^†, Refine SG= Nimble=Deploy=MPower RX= Boost=Draft, Retain SG^†, Signal FSU^†, Travallas, Triton* C,* Triton K*^†
Triazolopyrimidine “TZP”	florasulam	PrePass Flex=Priority=MPower Battlefront= Blitz=FirstPass	Avenza^†, Broadband, Cirpreme/Cirpreme XC^†, Inferno Trio, Frontline XL= Topline^†, Frontline 2,4-D^†, HotShot^†, Korrex II^†, Paradigm^†, PrePass XC^†, MPower Battlefront CM^†=Spectrum^†, Stellar^†=Outshine^†, Stellar XL, Tridem^†
pyroxsulam	Simplicity	Rexade^†, Tandem^†, Tridem*^†
Sulfonylamino- carbonyltriazolinone “SACT”	flucarbazone	Everest/Sierra 3.0, Everest/Sierra 3.0 AG	Batalium, Inferno Duo, Inferno Trio
propoxycarbazone- sodium	Olympus	–
thiencarbazone	Varro	Luxxur^†, Predicade, Velocity m3
Mitotic Inhibitor (3) Dinitroaniline (DNA)	ethalfluralin	Edge	–
trifluralin	Treflan=Bonanza=Rival	Fortress MicroActiv*
Benzamide	propyzamide	Kerb (SC, 50WP)	–
Growth Regulators (4) Phenoxy acetic acids Benzoic acids	2,4-D amine	2,4-D, others	Restore II
2,4-D ester	2,4-D Ester, Salvo	Approve=Leader=Thrasher=Thumper, Blackhawk, Turboprop,* Estaprop XT=Dichlorprop DX, Enforcer D, Frontline 2,4-D^†, Flurox- 24^†=Rush 24^†= MPower Foxxy Pro^†,=Attain XC^†, Ko-Act^†, Octtain XL, Reclaim^†, Reclaim II^†, Rexade^†, Retain SG, TraxosTwo^†, Triton K*^†
2,4-D choline	–	Grazon XC
2,4-DB	Embutox, Cobutox, Caliber	–
Dichorprop (2,4-DP)	–	Turboprop, Estaprop XT=Dichlorprop DX, Optica Trio
MCPA amine	MCPA Amine	Optica Trio, Sword, Target, Tracker XP
MCPA ester	MCPA LV ester	Batalium, Buctril M=Badge II=Logic M= Mextrol 450=MPower Buck M, Curtail M, Enforcer M=ForceFighter^†, Enforcer MSU^†, Frontline XL, Goldwing, Pixarro^†, Predicade^†, MPower Foxxy CM^†=Prestige XC^†, Prestige XL, Spectrum^†=MPower Battlefront CM^†, Stellar^†=Outshine^†, Stellar XL, Topline^†, Trophy^†=MPower Foxxy M^†=Rush M*^†
MCPA K+	Various	Clovitox Plus, Topside, Tropotox Plus
MCPA Na (sodium)	–	–
MCPB	–	Clovitox Plus, Topside, Tropotox Plus
Mecoprop–p (MCBP)	Mecoprop-P	Optica Trio, Sword, Target, Tracker XP
dicamba	Engenia	–
bapma salt
Dimethylamine salt	Oracle, Dicamba L	Express FX, Intruvix†, Korrex II†, Sword, Tracker XP, Triton K
Digycolamine salt	Banvel VM, FeXapan=XtendiMax	Pulsar, Target, Roundup Xtend
Sodium (Na) salt	–	Distinct=Overdrive
Isopropylamine	–	Glykamba*
Pyridine carboxilic acid	aminopyralid	–	Restore II, Reclaim†, Reclaim II†
aminocyclopyrachlor	–	Navius/Navius Flex
clopyralid	Lontrel=Pyralid=MPower Clobber	Cirpreme/Cirpreme XC†, Curtail M=MPower Clobber M, MPower Clobber G†=Eclipse†, Momentum, MPower Foxxy CM†=Prestige XC†, Prestige XL, Salute†, MPower Battlefront CM=Spectrum†*
fluroxypyr	Ikwin=Fluro Star	Altitude FX2†, Attain XC†=Flurox-24†= MPower Foxxy Pro†=Rush 24†,* Avenza†, Axial Xtreme, Axial Xtreme iPak†, Barricade II†=MPower Foxxy R†,* Batalium, Cirpreme XC†, EnforcerD, Enforcer M=ForceFighter†,* Enforcer MSU†, Infinity FX†, Momentum, OcTTain XL, Pixarro†, Predicade†,* Prestige XC†= MPower Foxxy CM†=Esteem†, Prestige XL, Pulsar, Retain SG†, Rezuvant†, Signal FSU†, Stellar†=Outshine†, Stellar XL, Tandem†, Travallas, TraxosTwo†, Tridem†, Trophy†=MPower Foxxy M†=Rush M†*
halauxifen	–	Cirpreme/Cirpreme XC†, Paradigm†, Pixarro†, Rexade†, Rezuvant†*
picloram	Tordon 22K	Grazon XC
Quinoline carboxilic acid	quinclorac (dicots)	Clever=Ingenious=MasterLine Quinclorac, Facet L	Triton C*
Photosystem II Inhibitor (5) Triazine	atrazine	Aatrex	Primextra II Magnum*
simazine	Princep Nine-T=Simazine 480	–
Triazinone	hexazinone	Velpar DF CU	–
metribuzin	Sencor=TriCor=Squadron=Buzzin, Metrix SC	Tiedown†*
Photosystem II Inhibitor (6)	bentazon	Basagran=Benta Super=Broadloom= MPower Boa, Basagran Forté	Hurricane, Viper ADV
bromoxynil	Pardner=MPower Buck; Brotex 240=Bromotril II=Bromoxynil 240 EC; Brotex 480=Brotex 4AT; Koril 235	Approve=Leader=Thrasher=Thumper, Axial iPak, Axial Xtreme iPak†, Batalium, Buctril M=Badge=Logic M=Mextrol 450, Conquer†, Conquer II, Enforcer D, Enforcer M=ForceFighter†, Enforcer MSU†, HotShot†, Infinity, Infinity FX†, Tundra, Velocity m3*
Photosystem II Inhibitor (7)	linuron	Lorox=Linuron 400	–
Lipid Synthesis Inhibition (8) Thiocarbamate	EPTC	Eptam	–
triallate	Avadex Brands	Fortress MicroActive*
EPSP Synthase Inhibitor (9)	glyphosate-IPA, K, DMA	several – see page 227	CleanStart†, Eclipse III /XC†=MPower Clobber G†, Flexstar GT, Glykamba, PrePass XC †, Roundup Xtend
Glutamine Synthet- ase Inhibitor (10)	glufosinate	Good Harvest, Liberty 150=MPower Vigor, Liberty 200	–
Bleaching: DOXP Synthase Inhib. (13)	clomazone	Command	Command Charge†*
PPO (Protox) Inhibitor (14) Diphenyletherimine	acifluorfen	Ultra Blazer	Hurricane*
fomesafen	Reflex	Flexstar GT*
N-phenylphthalimide	flumioxazin	Chateau=Valtera	Fierce*
Phenylpyrazole	pyraflufen	–	BlackHawk, Goldwing
Pyrimidinedione	saflufenacil	Heat LQ	Heat Complete†*
Triazolinone	carfentrazone	Aim EC	Authority Charge†, CleanStart†,* Command Charge†, Conquer†, Conquer II, Focus* († old form), Inferno Trio, Intruvix†*
sulfentrazone	Authority	Authority Charge†, Authority Supreme†*
Very Long Chain Fatty Acid Inhibitor (15) Acetamide	dimethanamid-P	Frontier Max	–
Chloroacetamide	S-metolachlor+ safener	Dual II Magnum	Primextra II Magnum, Tiedown†
pyroxasulfone	Zidua SC	Authority Supreme†, Fierce, Focus* († old form), Heat Complete†*
Auxin Inhibitor (19)	diflufenzopyr	–	Distinct=Overdrive
Photosystem I Inhibitor (22)	diquat	Reglone=Armory=Bolster=Craven=Desica= Diquat 240=Drifast=Guardsman Diquat= MasterLine Diquat= MPower Clone=Stage, Reglone Ion, Reward	–
paraquat	Gramoxone	Gramoxone
Unknown (26)	quinclorac (grass)	Clever=Ingenious=MasterLine Quinclorac; Facet L	–
Unkown (no Group)	Ammonium salt of Fatty Acid	Axxe	–
Bleaching: HPPD Inhibition(27) Pyrazolone	pyrasulfotole	–	Axial iPak†, Axial Xtreme iPak†, Infinity, Infinity FX†, Tundra, Velocity m3
tolpyralate	Shieldex	–
topramezone	Impact=Armezon	–

Adapted from WSSA Herbicide Classification System For Resistant Weed Management. Weed Technol. 17:606-608 and the NDSU Weed Control Guide.

Contact herbicides = Groups 5, 6, 7, 10, 14, and 22.

*Products contain more than one active ingredient and appear in more than one group. In some instances, both active ingredients act to kill the same weed using different modes of action. Using these products or tank mixes of products from different groups that control the same high risk weed (see the Herbicide Resistant Weeds in Western Canada chart on page 51) will slow down the process of developing weed resistance.

New herbicides do not necessarily have a unique mode of action and may fall within the groups listed in the charts.

Herbicides that have the same mode of action may not control the same weed spectrum or have the same crop safety. For example, Assert and Ally have the same mode of action; however, Assert controls wild oats while Ally does not.

† Products are packaged with multiple components in one package. Each component may also have multiple active ingredients.

How to Identify Weed Resistance

It is important to avoid confusing herbicide failure caused by resistance with herbicide failure caused by various other factors (such as weather or application errors). When a herbicide fails to control weeds because of weather or application factors, that herbicide may work in the field the next season. But when herbicides fail because of the development of resistance, they will fail in subsequent years, regardless of weather or application procedures.

Herbicide resistance should be suspected under the following conditions:

A weed species that the herbicide controlled in previous seasons now escapes the treatment, while other weeds that appear on the label continue to be controlled in the field.
The escapes cannot be attributed to adverse weather or emergence after application (if a post-emergence product is in question).
Irregular-shaped patches of a weed develop where the herbicide gives little or no control.
Records of the past history of the field show repeated use of the same herbicide, or combinations of herbicides, that kill the weed in question in the same way.

Table 10. Herbicide-Resistant Weeds in Western Canada

Weed	Herbicide Group	Locations Confirmed
Barnyard grass	Group 2	MB
Canada Fleabane	Group 9	Occurs in several US states
Canada Fleabane	Multiple Resistant: Groups 2 & 9	Occurs in Ontario
Cleavers	Group 2	AB, MB, SK
	Group 4	AB
	Multiple combinations of: Groups 2 & 4	AB
Chickweed	Group 2	AB, MB, SK
Cow Cockle	Group 2	AB
Downy Brome	Group 2	Occurs in Montana
Foxtail, green	Group 1	AB, MB, SK
	Group 2	MB, SK
	Group 3	AB, MB, SK
	Multiple combinations of: Groups 1 & 3	MB, SK
Foxtail, yellow	Group 1 + 2	MB
Hemp-nettle	Group 2	AB, MB
	Group 4	AB
	Multiple combinations of: Groups 2 & 4	AB
Kochia	Group 2	AB, MB, SK (overwhelming majority)
	Group 4 (dicamba and fluroxypyr)	SK
	Group 5	Occurs in North Dakota and Montana
	Group 9 (glyphosate)	AB, MB, SK
	Multiple Resistant: Groups 2 & 9	AB, MB, SK
	Multiple Resistant: Groups 2 & 4	SK
	Multiple Resistant: Groups 2, 4 (dicamba) & 9	AB
	Multiple Resistant: Groups 2, 4 & 9	AB
Lamb’s-quarters	Group 2	SK
Lamb’s-quarters	Group 5	Occurs in Ontario
Marshelder (false ragweed)	Group 2	Occurs in North Dakota
Mustard, Ball	Group 2	AB
Mustard, Wild	Group 2	AB, MB, SK
	Group 4	MB
	Group 5	MB
Narrow-leaved hawk’s-beard	Group 2	AB
Persian Darnel	Group 1	AB, SK
Ragweed, giant	Group 2 & 9	Occurs in Ontario, Minnesota
Redroot pigweed	Group 2	MB, SK
Redroot pigweed	Group 5	Occurs in Ontario
Russian thistle	Group 2	AB, SK
Russian thistle	Group 9	Occurs in Montana
Shepherd’s-purse	Group 2	AB, MB, SK
Smartweed, pale	Group 2	MB
Spiny Annual Sow-thistle	Group 2	AB, MB
Stinkweed	Group 2	AB, MB, SK
Waterhemp	Group 2 & 9	Occurs in North Dakota, MB
Waterhemp	Group 2, 5, 9 & 14	Ontario
Wild buckwheat	Group 2	AB
Wild oat	Group 1	AB, MB, SK
	Group 2	AB, MB, SK
	Group 8	AB, MB, SK
	Multiple combinations of: Groups 1 & 2, Groups 1 & 8, Groups 2 & 8, Groups 1, 2 & 8, Groups 1, 2, 8 & 25, Groups 1, 2, 8, 14, 15 (MB)	AB, MB, SK

See Table 8 on page 45 for a complete list of products in each Herbicide Resistance Group.

If Weed Resistance Develops on Your Farm

It is important to identify weed resistance before it spreads across your farm. Plan on conducting a “patch watch” scouting program this summer to identify suspicious patches before they become difficult to manage. Resistant weed patches have been identified on fields where producers were unaware of their existence.

Your patch watch program should begin shortly after spraying and continue through July after the crop has headed out and most weeds are visible from a distance. If you find suspicious looking patches, contact your local agricultural office or crop protection company representative to assist you in confirming weed resistance. If resistance is suspected:

Map the location of the patches and mark them with stakes so you will remember their location.
Mow, cultivate or spot spray the patches. Resistant patches should not be allowed to produce seed.
Patchy areas should NOT be harvested with the rest of the field. Harvest these areas separately, and make sure to clean all harvesting equipment before leaving the area to prevent the spread of seeds across the field or a neighbouring field.
Check patches each year to monitor their spread. Keeping your resistant weeds isolated to a manageable patch is easier than dealing with an entire field of resistant weeds.