INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE
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Herbicide Resistant Horseweed Globally
(Conyza canadensis)
Herbicide Resistant Horseweed Globally
(Conyza canadensis)
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Herbicide Resistant Horseweed Globally
(Conyza canadensis)
#CountryFirstYearSituationActive IngredientsSite of Action
1 BelgiumBelgium 1989 Corn (maize), Nurseries, and Roadsides atrazine 3 PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
 		61Conyza canadensisHorseweed35
2 BelgiumBelgium 1998 Nurseries paraquat 3 PS I Electron Diversion HRAC Group 22 (Legacy D)
 		61Conyza canadensisHorseweed1145
3 BrazilBrazil 2005 Fruit, Orchards, and Soybean glyphosate 5 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5273
4 Canada (Ontario) CanadaOntario1993 Peaches paraquat 7 PS I Electron Diversion HRAC Group 22 (Legacy D)
 		61Conyza canadensisHorseweed48
5 Canada (Ontario) CanadaOntario2010 Soybean glyphosate 7 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5665
6 Canada (Ontario) CanadaOntario2011 Soybean cloransulam-methyl, and glyphosate 7 Multiple Resistance: 2 Sites of Action
Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5666
7 ChinaChina 2006 Orchards glyphosate 9 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5277
8 Czech RepublicCzech Republic 1987 Corn (maize), Nurseries, Orchards, Pastures, Railways, and Roadsides atrazine 12 PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
 		61Conyza canadensisHorseweed83
9 Czech RepublicCzech Republic 2007 Railways glyphosate 12 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5317
10 FranceFrance 1981 Cropland atrazine 17 PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
 		61Conyza canadensisHorseweed460
11 FranceFrance 1988 Orchards linuron 17 PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
 		61Conyza canadensisHorseweed451
12 FranceFrance 2019 Grapes glyphosate 17 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed18198
13 GreeceGreece 2012 Grapes, and Orchards glyphosate 19 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5692
14 HungaryHungary 2016 Grapes glyphosate 20 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed15070
15 IsraelIsrael 1993 Forests, Industrial sites, and Roadsides atrazine, chlorsulfuron, imazapyr, metribuzin, pyrithiobac-sodium, and sulfometuron-methyl 23 Multiple Resistance: 2 Sites of Action
Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
 		61Conyza canadensisHorseweed109
16 ItalyItaly 2011 Orchards glyphosate 24 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5617
17 JapanJapan 1980 Grapes, Orchards, Railways, and Roadsides paraquat 25 PS I Electron Diversion HRAC Group 22 (Legacy D)
 		61Conyza canadensisHorseweed119
18 JapanJapan 2014 Railways glyphosate 25 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed10999
19 PolandPoland 1983 Orchards simazine 33 PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
 		61Conyza canadensisHorseweed168
20 PolandPoland 2000 Railways imazapyr 33 Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
 		61Conyza canadensisHorseweed5081
21 PolandPoland 2010 Railways glyphosate 33 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5622
22 PortugalPortugal 2011 Olive glyphosate 34 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed7824
23 South KoreaSouth Korea 2017 Orchards glyphosate 27 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed16077
24 SpainSpain 1987 Corn (maize), Orchards, and Roadsides atrazine, and simazine 38 PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
 		61Conyza canadensisHorseweed177
25 SpainSpain 2006 Orchards glyphosate 38 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5319
26 SwitzerlandSwitzerland 1982 Corn (maize), Nurseries, Orchards, Pastures, Railways, and Roadsides atrazine, and simazine 41 PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
 		61Conyza canadensisHorseweed203
27 SwitzerlandSwitzerland 2021 Grapes glyphosate 41 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed24248
28 United KingdomUnited Kingdom 1982 Orchards simazine 44 PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
 		61Conyza canadensisHorseweed362
29 United States (Mississippi) United StatesMississippi1994 Soybean paraquat 45 PS I Electron Diversion HRAC Group 22 (Legacy D)
 		61Conyza canadensisHorseweed1109
30 United States (Delaware) United StatesDelaware2000 Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5086
31 United States (Tennessee) United StatesTennessee2001 Cotton, and Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5122
32 United States (Ohio) United StatesOhio2001 Soybean chlorimuron-ethyl, and cloransulam-methyl 45 Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
 		61Conyza canadensisHorseweed5157
33 United States (Kentucky) United StatesKentucky2001 Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5208
34 United States (Ohio) United StatesOhio2002 Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5127
35 United States (Indiana) United StatesIndiana2002 Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5128
36 United States (Maryland) United StatesMaryland2002 Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5129
37 United States (New Jersey) United StatesNew Jersey2002 Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5130
38 United States (Michigan) United StatesMichigan2002 Corn (maize), and Soybean chlorimuron-ethyl, and cloransulam-methyl 45 Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
 		61Conyza canadensisHorseweed5172
39 United States (Michigan) United StatesMichigan2002 Blueberries atrazine, diuron, and simazine 45 PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
 		61Conyza canadensisHorseweed5173
40 United States (Michigan) United StatesMichigan2002 Blueberries diuron 45 PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
 		61Conyza canadensisHorseweed5174
41 United States (Missouri) United StatesMissouri2002 Corn (maize), Cotton, and Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5260
42 United States (Ohio) United StatesOhio2003 Soybean chlorimuron-ethyl, cloransulam-methyl, and glyphosate 45 Multiple Resistance: 2 Sites of Action
Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5158
43 United States (Arkansas) United StatesArkansas2003 Cotton glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5187
44 United States (Mississippi) United StatesMississippi2003 Corn (maize), Cotton, Rice, and Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5195
45 United States (North Carolina) United StatesNorth Carolina2003 Cotton glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5200
46 United States (Delaware) United StatesDelaware2003 Soybean paraquat 45 PS I Electron Diversion HRAC Group 22 (Legacy D)
 		61Conyza canadensisHorseweed5257
47 United States (Pennsylvania) United StatesPennsylvania2003 Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5258
48 United States (California) United StatesCalifornia2005 Corn (maize), Fencelines, Grapes, Orchards, Roadsides, and Wheat glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5250
49 United States (Illinois) United StatesIllinois2005 Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5276
50 United States (Kansas) United StatesKansas2005 Cotton, and Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5308
51 United States (Virginia) United StatesVirginia2005 Corn (maize), and Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5559
52 United States (Indiana) United StatesIndiana2005 Soybean chlorimuron-ethyl, and cloransulam-methyl 45 Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
 		61Conyza canadensisHorseweed7836
53 United States (Nebraska) United StatesNebraska2006 Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5496
54 United States (Michigan) United StatesMichigan2007 Nurseries glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5312
55 United States (Mississippi) United StatesMississippi2007 Soybean glyphosate, and paraquat 45 Multiple Resistance: 2 Sites of Action
PS I Electron Diversion HRAC Group 22 (Legacy D)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5384
56 United States (West Virginia) United StatesWest Virginia2007 Corn (maize), and Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed7774
57 United States (Oklahoma) United StatesOklahoma2009 Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5528
58 United States (South Dakota) United StatesSouth Dakota2010 Corn (maize), and Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5634
59 United States (Delaware) United StatesDelaware2010 Soybean, and Wheat glyphosate, thifensulfuron-methyl, and tribenuron-methyl 45 Multiple Resistance: 2 Sites of Action
Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5710
60 United States (Iowa) United StatesIowa2011 Corn (maize), and Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed5567
61 United States (Kansas) United StatesKansas2011 Corn (maize), Cotton, Soybean, and Wheat chlorsulfuron, iodosulfuron-methyl-Na, metsulfuron-methyl, rimsulfuron, thiencarbazone-methyl, thifensulfuron-methyl, and tribenuron-methyl 45 Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
 		61Conyza canadensisHorseweed7806
62 United States (Alabama) United StatesAlabama2013 Corn (maize), Cotton, and Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed7783
63 United States (Wisconsin) United StatesWisconsin2013 Soybean glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed7823
64 United States (Illinois) United StatesIllinois2013 Soybean cloransulam-methyl 45 Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
 		61Conyza canadensisHorseweed7865
65 United States (California) United StatesCalifornia2014 Almonds glyphosate, and paraquat 45 Multiple Resistance: 2 Sites of Action
PS I Electron Diversion HRAC Group 22 (Legacy D)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed9943
66 United States (Montana) United StatesMontana2015 Roadsides glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed11011
67 United States (Oklahoma) United StatesOklahoma2018 Cotton, Soybean, and Wheat chlorsulfuron, and metsulfuron-methyl 45 Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
 		61Conyza canadensisHorseweed17149
68 United States (Oregon) United StatesOregon2023 Fallow, and Wheat glyphosate 45 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
 		61Conyza canadensisHorseweed27286
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