INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

HRAC GROUP 5 (LEGACY C1 C2) RESISTANT SMOOTH PIGWEED
(Amaranthus hybridus (syn: quitensis))


PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)

United States, Maryland
INTRODUCTION SMOOTH PIGWEED
Smooth Pigweed (Amaranthus hybridus (syn: quitensis)) is a dicot weed in the Amaranthaceae family.  In Maryland this weed first evolved resistance to Group 5 (Legacy C1 C2) herbicides in 1972 and infests Corn (maize), and Cropland.   Group 5 (Legacy C1 C2) herbicides are known as PSII inhibitors - Serine 264 Binders (Inhbition of Photosynthesis at PSll - Serine 264 Binders ).  Research has shown that these particular biotypes are resistant to atrazine and they may be cross-resistant to other Group 5 (Legacy C1 C2) herbicides.

The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

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QUIK STATS (last updated Sep 15, 2000 )

Common NameSmooth Pigweed
SpeciesAmaranthus hybridus (syn: quitensis)
GroupPSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
Herbicidesatrazine
LocationUnited States, Maryland
Year1972
Situation(s)Corn (maize), and Cropland
Contributors - (Alphabetically)Ronald Ritter 
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ACADEMIC ASPECTS

Confirmation Tests

Field, Greenhouse, and Laboratory trials comparing a known susceptible Smooth Pigweed biotype with this Smooth Pigweed biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.
 
Genetics

Genetic studies on HRAC Group 5 resistant Smooth Pigweed have not been reported to the site.  There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature
 
Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database.  If you know anything about the mechanism of resistance for this biotype then please update the database.
 
Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes.  If you have any information pertaining to the fitness of Group 5 (Legacy C1 C2) resistant Smooth Pigweed from Maryland please update the database.
 
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CONTRIBUTING WEED SCIENTISTS

RONALD RITTER
Professor
University Of Maryland
Plant Science and Landscape Architecture
1118 H. J. Patterson Hall
College Park, 20742 , Maryland
United States
Email Ronald Ritter
Web   : Web Site Link

ACKNOWLEDGEMENTS

The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Maryland have been instrumental in providing you this information. Particular thanks is given to Ronald Ritter for providing detailed information.
Herbicide Resistant Smooth Pigweed Globally
(Amaranthus hybridus (syn: quitensis))
Herbicide Resistant Smooth Pigweed Globally
(Amaranthus hybridus (syn: quitensis))
Drag a column header and drop it here to group by that column
Herbicide Resistant Smooth Pigweed Globally
(Amaranthus hybridus (syn: quitensis))
#CountryFirstYearSituationActive IngredientsSite of Action
1 ArgentinaArgentina 1996 Soybean chlorimuron-ethyl, and imazethapyr 48 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5099
2 ArgentinaArgentina 2013 Soybean glyphosate 48 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed6757
3 ArgentinaArgentina 2014 Corn (maize), and Soybean glyphosate, and imazethapyr 48 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)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed9948
4 ArgentinaArgentina 2016 Soybean 2,4-D, dicamba, and glyphosate 48 Multiple Resistance: 2 Sites of Action
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)
Auxin Mimics ( HRAC Group 4 (Legacy O)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed17107
5 ArgentinaArgentina 2016 Soybean 2,4-D, and dicamba 48 Auxin Mimics ( HRAC Group 4 (Legacy O)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed17108
6 ArgentinaArgentina 2021 Soybean fomesafen 48 Inhibition of Protoporphyrinogen Oxidase ( HRAC Group 14 (Legacy E)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed23243
7 BoliviaBolivia 2002 Soybean chlorimuron-ethyl, imazamox, imazethapyr, and oxasulfuron 4 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5242
8 BoliviaBolivia 2005 Soybean fomesafen, lactofen, and sulfentrazone 4 Inhibition of Protoporphyrinogen Oxidase ( HRAC Group 14 (Legacy E)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5411
9 BrazilBrazil 2018 Soybean chlorimuron-ethyl, and glyphosate 5 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)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed18184
10 Canada (Ontario) CanadaOntario2004 Corn (maize) bentazon, and bromoxynil 7 PSII inhibitors - Histidine 215 Binders ( HRAC Group 6 (Legacy C3)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5472
11 FranceFrance 1980 Corn (maize) atrazine 17 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed453
12 IsraelIsrael 1986 Cropland atrazine 23 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed101
13 ItalyItaly 1978 Corn (maize) atrazine 24 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed114
14 ItalyItaly 2018 Soybean imazamox, and thifensulfuron-methyl 24 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed27281
15 ParaguayParaguay 2022 Corn (maize), and Soybean chlorimuron-ethyl, and glyphosate 46 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)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed24252
16 South AfricaSouth Africa 1993 Corn (maize) atrazine 37 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed193
17 South AfricaSouth Africa 2024 Corn (maize), and Soybean glyphosate 37 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed27287
18 SpainSpain 1985 Corn (maize) atrazine 38 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed175
19 SwitzerlandSwitzerland 1982 Vegetables simazine 41 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed198
20 United States (Maryland) United StatesMaryland1972 Corn (maize), and Cropland atrazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed429
21 United States (Virginia) United StatesVirginia1976 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed273
22 United States (Delaware) United StatesDelaware1977 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed492
23 United States (North Carolina) United StatesNorth Carolina1980 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed262
24 United States (Pennsylvania) United StatesPennsylvania1980 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed264
25 United States (New Jersey) United StatesNew Jersey1980 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed494
26 United States (New York) United StatesNew York1980 Corn (maize) atrazine, metribuzin, and simazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5225
27 United States (Wisconsin) United StatesWisconsin1985 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed418
28 United States (Kentucky) United StatesKentucky1987 Corn (maize) atrazine, and simazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed489
29 United States (Kentucky) United StatesKentucky1992 Soybean chlorimuron-ethyl, flumetsulam, imazaquin, imazethapyr, nicosulfuron, primisulfuron-methyl, and thifensulfuron-methyl 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed490
30 United States (Illinois) United StatesIllinois1993 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed236
31 United States (Virginia) United StatesVirginia1994 Corn (maize), and Soybean imazaquin, and imazethapyr 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed278
32 United States (Illinois) United StatesIllinois1998 Soybean imazethapyr, and primisulfuron-methyl 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed7859
33 United States (Delaware) United StatesDelaware2000 Vegetables imazethapyr 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5160
34 United States (Illinois) United StatesIllinois2000 Corn (maize) atrazine, imazethapyr, and primisulfuron-methyl 45 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)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed7860
35 United States (Ohio) United StatesOhio2001 Soybean flumetsulam, and thifensulfuron-methyl 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5233
36 United States (Michigan) United StatesMichigan2002 Soybean chlorimuron-ethyl, imazamox, and thifensulfuron-methyl 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5170
37 UruguayUruguay 2022 Corn (maize), and Soybean glyphosate 73 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed24255
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