International Survey of Herbicide-Resistant Weeds

Countries Weeds Herbicides Mutations Graphs References Researchers
GROUP G/9 RESISTANT SMOOTH PIGWEED
(Amaranthus hybridus (syn: quitensis))


Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9)

South Africa, KwaZulu Natal
INTRODUCTION SMOOTH PIGWEED
Smooth Pigweed (Amaranthus hybridus (syn: quitensis)) is a dicot weed in the Amaranthaceae family.  In South Africa this weed first evolved resistance to Group G/9 herbicides in 2024 and infests Corn (maize), and Soybean.   Group G/9 herbicides are known as Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (Inhibition of EPSP synthase).  Research has shown that these particular biotypes are resistant to glyphosate and they may be cross-resistant to other Group G/9 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 May 24, 2024 )

Common NameSmooth Pigweed
SpeciesAmaranthus hybridus (syn: quitensis)
GroupInhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9)
Herbicidesglyphosate
LocationSouth Africa, KwaZulu Natal
Year2024
Situation(s)Corn (maize), and Soybean
Contributors - (Alphabetically)Carl Reinhardt, and Nhlanhla Shabangu 
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NOTES ABOUT THIS BIOTYPE

GENERAL

Carl Reinhardt

Shabangu, N.M., Simelane, N.A., Reinhardt, C.F., Marais, D. & Vorster, B.J. (2024) First report of target-site resistance to glyphosate in Amaranthus hybridus L. in the Republic of South Africa. Weed Research, 1–12. Available from: https://doi.org/10.1111/wre.12635

First report of target-site resistance to glyphosate in Amaranthus hybridus L. in the Republic of South Africa Nhlanhla M., Nonduduzo A. Simelane, Carl F. Reinhardt, Diana Marais and Barend J. Vorster   Abstract Amaranthus hybridus L. is a major weed for summer crops. Although A. hybridus has been a known crop weed in the Republic of South Africa (RSA) for a long time, herbicide resistance has not been a problem. Nevertheless, A. hybridus populations from KwaZulu Natal (KZN) Province have caught the attention of farmers since glyphosate has been progressively becoming less effective in controlling the species. This study aimed to evaluate herbicide resistance in A. hybridus and the underlying mechanisms of resistance. Seeds from 50 glyphosate-resistant plants were collected from fields at Bergville and Winterton in KZN and compared with a susceptible population from Hendrina (Mpumalanga Province). Glasshouse screening was conducted where glyphosate (Roundup® PowerMax) was applied at 6-leaf stage, at doses 0, 540, 1080 (recommended dose), 2160 and 4320 g ae ha1. Surviving plants were sampled for molecular analysis to establish any target site mutations in the EPSPS gene that confer glyphosate resistance. Dose–response assay indicated 100% control in the Hendrina population, variation in the control of the Winterton population and 100% survival in the Bergville population. Molecular analysis indicated a rare triple mutation (TAP-IVS) in the KZN populations. This kind of mutation endows a high level of glyphosate resistance, which explains why these populations survived even the 4 dose. These findings confirmed the first cases of glyphosate-resistant A. hybridus and established the mechanism of resistance as target site mutations in the EPSPS gene reported in the RSA. These findings will serve as a base for other herbicide resistance cases and the development of initiatives to control and minimize the spread of this weed in the RSA.

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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 Group G/9 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 G/9 resistant Smooth Pigweed from South Africa 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 G/9 resistant Smooth Pigweed from South Africa please update the database.
 
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CONTRIBUTING WEED SCIENTISTS

CARL REINHARDT
Professor
University of Pretoria
Dept of Plant Production and Soil Science
P/Bag X20
Pretoria, 0028, Gauteng
South Africa
Email Carl Reinhardt
NHLANHLA SHABANGU
Mr
University of Pretoria
Plant and Soil Sciences
538 Grosvenor St
Hatfield, Pretoria, 0028
Pretoria, 0028, Gauteng
South Africa
Email Nhlanhla Shabangu

ACKNOWLEDGEMENTS

The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in South Africa have been instrumental in providing you this information. Particular thanks is given to Carl Reinhardt, and Nhlanhla Shabangu 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 (B/2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5099
2 ArgentinaArgentina 2013 Soybean glyphosate 48 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9)
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 (B/2)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9)
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 (G/9)
Auxin Mimics (O/4)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed17107
5 ArgentinaArgentina 2016 Soybean 2,4-D, and dicamba 48 Auxin Mimics (O/4)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed17108
6 ArgentinaArgentina 2021 Soybean fomesafen 48 Inhibition of Protoporphyrinogen Oxidase (E/14)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed23243
7 BoliviaBolivia 2002 Soybean chlorimuron-ethyl, imazamox, imazethapyr, and oxasulfuron 4 Inhibition of Acetolactate Synthase (B/2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5242
8 BoliviaBolivia 2005 Soybean fomesafen, lactofen, and sulfentrazone 4 Inhibition of Protoporphyrinogen Oxidase (E/14)
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 (B/2)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed18184
10 Canada (Ontario) CanadaOntario2004 Corn (maize) bentazon, and bromoxynil 7 PSII inhibitors - Histidine 215 Binders (C3/6)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5472
11 FranceFrance 1980 Corn (maize) atrazine 17 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed453
12 IsraelIsrael 1986 Cropland atrazine 23 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed101
13 ItalyItaly 1978 Corn (maize) atrazine 24 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed114
14 ItalyItaly 2018 Soybean imazamox, and thifensulfuron-methyl 24 Inhibition of Acetolactate Synthase (B/2)
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 (B/2)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed24252
16 South AfricaSouth Africa 1993 Corn (maize) atrazine 37 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed193
17 South AfricaSouth Africa 2024 Corn (maize), and Soybean glyphosate 37 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed27287
18 SpainSpain 1985 Corn (maize) atrazine 38 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed175
19 SwitzerlandSwitzerland 1982 Vegetables simazine 41 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed198
20 United States (Maryland) United StatesMaryland1972 Corn (maize), and Cropland atrazine 45 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed429
21 United States (Virginia) United StatesVirginia1976 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed273
22 United States (Delaware) United StatesDelaware1977 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed492
23 United States (North Carolina) United StatesNorth Carolina1980 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed262
24 United States (Pennsylvania) United StatesPennsylvania1980 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed264
25 United States (New Jersey) United StatesNew Jersey1980 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders (C1 C2/5)
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 (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5225
27 United States (Wisconsin) United StatesWisconsin1985 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed418
28 United States (Kentucky) United StatesKentucky1987 Corn (maize) atrazine, and simazine 45 PSII inhibitors - Serine 264 Binders (C1 C2/5)
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 (B/2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed490
30 United States (Illinois) United StatesIllinois1993 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed236
31 United States (Virginia) United StatesVirginia1994 Corn (maize), and Soybean imazaquin, and imazethapyr 45 Inhibition of Acetolactate Synthase (B/2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed278
32 United States (Illinois) United StatesIllinois1998 Soybean imazethapyr, and primisulfuron-methyl 45 Inhibition of Acetolactate Synthase (B/2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed7859
33 United States (Delaware) United StatesDelaware2000 Vegetables imazethapyr 45 Inhibition of Acetolactate Synthase (B/2)
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 (B/2)
PSII inhibitors - Serine 264 Binders (C1 C2/5)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed7860
35 United States (Ohio) United StatesOhio2001 Soybean flumetsulam, and thifensulfuron-methyl 45 Inhibition of Acetolactate Synthase (B/2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5233
36 United States (Michigan) United StatesMichigan2002 Soybean chlorimuron-ethyl, imazamox, and thifensulfuron-methyl 45 Inhibition of Acetolactate Synthase (B/2)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed5170
37 UruguayUruguay 2022 Corn (maize), and Soybean glyphosate 73 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9)
12Amaranthus hybridus (syn: quitensis)Smooth Pigweed24255
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