International Survey of Herbicide-Resistant Weeds

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HRAC GROUP 2 (LEGACY B) RESISTANT SMOOTH PIGWEED
(Amaranthus hybridus (syn: quitensis))


Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Italy, Friuli Venezia Giulia region
INTRODUCTION SMOOTH PIGWEED
Smooth Pigweed (Amaranthus hybridus (syn: quitensis)) is a dicot weed in the Amaranthaceae family.  In Italy this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2018 and infests Soybean.   Group 2 (Legacy B) herbicides are known as Inhibition of Acetolactate Synthase (Inhibition of Acetolactate Synthase ).  Research has shown that these particular biotypes are resistant to imazamox, and thifensulfuron-methyl and they may be cross-resistant to other Group 2 (Legacy B) 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 Nov 03, 2023 )

Common NameSmooth Pigweed
SpeciesAmaranthus hybridus (syn: quitensis)
GroupInhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicidesimazamox, and thifensulfuron-methyl
LocationItaly, Friuli Venezia Giulia region
Year2018
Situation(s)Soybean
Contributors - (Alphabetically)Silvia Panozzo, Maurizio Sattin, and Laura Scarabel 
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NOTES ABOUT THIS BIOTYPE

GENERAL

Maurizio Sattin

Diversity and spread of acetolactate synthase allelic variants at position 574 endowing resistance in Amaranthus hybridus in Italy.

Author(s) : Milani, A. ;  Panozzo, S. ;  Pinton, S. ;  Danielis, R. A. ;  Sattin, M. ;  Scarabel, L.

Author Affiliation : Institute for Sustainable Plant Protection (IPSP-CNR), 35020 Legnaro, Italy.

Author Email : silvia.panozzo@cnr.it

Journal article : Plants 2023 Vol.12 No.2

Abstract : Poor control of Amaranthus spp. with herbicides inhibiting acetolactate synthase (ALS) has been observed for several years in soybean fields in north-eastern Italy, but to date only a few ALS-resistant populations have been confirmed. An extensive sampling of putatively resistant Amaranthus accessions was completed in the Friuli Venezia Giulia region, across an arable land area of about 3000 km2. In total, 58 accessions were tested to confirm their resistance status, recognize the Amaranthus species, identify the mutant ALS alleles endowing the resistance and determine the efficacy of 3 pre-emergence herbicides. Most accessions resulted in cross-resistance to thifensulfuron-methyl and imazamox. Genomic DNA were extracted from single seeds with a newly developed protocol; an allele-specific PCR assay revealed the presence of the 574-leucine in 20 accessions, of the 574-methionine in 22, and of both alleles in 9 accessions. The two variants showed a different spatial distribution. All resistant populations were ascribed to A. hybridus. A. hybridus resistant to ALS herbicides is well-established in this Italian region and its resistance is due to two ALS mutant alleles. Metribuzin, clomazone and metobromuron can be used as alternative herbicides to be applied in pre-emergence and they should be integrated into the management strategies to limit the spread of resistance.

ISSN : 2223-7747

DOI : 10.3390/plants12020332

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ACADEMIC ASPECTS

Confirmation Tests

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 2 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

Studies on the mechanism of resistance of Group 2 (Legacy B) resistant Smooth Pigweed from Italy indicate that resistance is due to an altered target site.  There may be a note below or an article discussing the mechanism of resistance in the Fact Sheets and Other Literature
 
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 2 (Legacy B) resistant Smooth Pigweed from Italy please update the database.
 
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CONTRIBUTING WEED SCIENTISTS

SILVIA PANOZZO
Weed Scientist
Italian National Research Council (CNR)
IBAF - Weed Research Unit
Viale dell'Università 16
Legnaro, 35020, Padova
Italy
Email Silvia Panozzo
MAURIZIO SATTIN
Senior Weed Scientist
Italian National Research Council (cnr)
IBAF - Weed Science Unit
Viale dell'Università 16
Legnaro, 35020, Padova
Italy
Email Maurizio Sattin
LAURA SCARABEL
Researcher
Institute of Agroenvironmental and Forest Biology
National Research Council (CNR)
viale dell'Università 16
Legnaro (PD), 35020, Padova
Italy
Email Laura Scarabel

ACKNOWLEDGEMENTS

The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Italy have been instrumental in providing you this information. Particular thanks is given to Silvia Panozzo, Maurizio Sattin, and Laura Scarabel 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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