Multiple resistant Kochia scoparia from Spain

INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

MULTIPLE RESISTANT KOCHIA
(Kochia scoparia)

Multiple Resistance: 3 Sites of Action
Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
Auxin Mimics HRAC Group 4 (Legacy O)

Spain, Catalonia

INTRODUCTION		KOCHIA
Kochia (Kochia scoparia) is a dicot weed in the Chenopodiaceae family. In Spain this weed first evolved multiple resistance (to 3 herbicide sites of action) in 2022 and infests Wheat, and Winter barley. Multiple resistance has evolved to herbicides in the Groups 2 (Legacy B), Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G), and Auxin Mimics HRAC Group 4 (Legacy O). These particular biotypes are known to have resistance to 2,4-D, glyphosate, MCPA, and thifensulfuron-methyl and they may be cross-resistant to other herbicides in the Groups 2 (Legacy B), Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G), and Auxin Mimics HRAC Group 4 (Legacy O). 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.

QUIK STATS (last updated May 30, 2025 )
Common Name	Kochia
Species	Kochia scoparia
Group	Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B) Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G) Auxin Mimics HRAC Group 4 (Legacy O)
Herbicides	2,4-D, glyphosate, MCPA, and thifensulfuron-methyl
Location	Spain, Catalonia
Year	2022
Situation(s)	Wheat, and Winter barley
Contributors - (Alphabetically)	Alicia Cirujeda, Jose María Montull , GERMAN MORA MARIN, Maria D. Osuna, and Joel Torra
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NOTES ABOUT THIS BIOTYPE

GENERAL

GERMAN MORA MARIN

A biotype of B. scoparia from Guissona (GUI-R), Catalonia, Spain, was collected in 2022 from winter cereal fields. This biotype exhibits multiple resistance to EPSPS, ALS inhibitors, and auxin mimics (3 MoAs) . This research was presented at the XIX Spanish Weed Science Society (SEMh, 2024) Congress and is currently under review in Pesticide Biochemistry and Physiology. Resistance mechanisms :

Resistance to glyphosate mediated by EPSPS gene amplification.
Resistance to ALS inhibitors (thifensulfuron) due to point mutations in the ALS gene (Pro197Ser, Pro197Leu, and Trp574Leu).
Resistance to synthetic auxins (2,4-D and MCPA) via enhanced metabolism.

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ACADEMIC ASPECTS

Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Kochia biotype with this Kochia 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, 9, 4 resistant Kochia 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 multiple resistant Kochia from Spain indicate that resistance is due to an altered target site, enhanced metabolism, and gene amplification. 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 multiple resistant Kochia from Spain please update the database.

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CONTRIBUTING WEED SCIENTISTS

ALICIA CIRUJEDA

Unidad de Sanidad Vegetal, Centro de Investigación y Tecnología Agroalimentaria de Aragón (CITA) Avda. Montañana 930 Zaragoza, 50059 , Aragon Spain Email Alicia Cirujeda

JOSE MARÍA MONTULL

Universitat de Lleida. Agrotecnio Agroalimentaria de Aragón (CITA) Rovira Roure 191 Lleida, 50059 , Catalonia Spain Email Jose María Montull

GERMAN MORA MARIN

PhD student Universitat de Lleida HBJ - Maleherbologia Carrer ROCA LABRADOR 12. Piso 5, puerta 3A Lleida, 25003, Cataluña Spain Email GERMAN MORA MARIN Web : Web Site Link

MARIA D. OSUNA

Researcher CICYTEX Crop Protection Finca La Orden Crta AV, km 372 Guadajira, 06187, Badajoz Spain Email Maria D. Osuna Web : Web Site Link

JOEL TORRA

Research Assistant University Of Lleida Depart. Hortofructicultura Botànica I Jardineria Rovira Roure 191, Etsea, Ed. 1 Lleida, 25198, Badajoz Spain Email Joel Torra Web : Web Site Link

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Spain have been instrumental in providing you this information. Particular thanks is given to Alicia Cirujeda, Jose María Montull , GERMAN MORA MARIN, Maria D. Osuna, and Joel Torra for providing detailed information.

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Herbicide Resistant Kochia Globally
(Kochia scoparia)

Country

FirstYear

Situation

Active Ingredients

Site of Action

Argentina

2025

Corn (maize), Fallow, Soybean, Sunflower, Wheat, and Winter barley

imazamox, and imazapyr

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Canada (Manitoba)

1988

Industrial sites, Spring Barley, and Wheat

chlorsulfuron, imazethapyr, metsulfuron-methyl, thifensulfuron-methyl, triasulfuron, and tribenuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Canada (Saskatchewan)

1988

Cropland, and Wheat

thifensulfuron-methyl, and tribenuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Canada (Alberta)

1989

Spring Barley, and Wheat

chlorsulfuron, metsulfuron-methyl, thifensulfuron-methyl, and tribenuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Canada (Alberta)

2012

Spring Barley, and Wheat

glyphosate, thifensulfuron-methyl, and tribenuron-methyl

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)

Canada (Saskatchewan)

2012

Canola, Spring Barley, and Wheat

glyphosate, thifensulfuron-methyl, and tribenuron-methyl

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)

Canada (Manitoba)

2014

Corn (maize), and Soybean

glyphosate, thifensulfuron-methyl, and tribenuron-methyl

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)

Canada (Saskatchewan)

2015

Spring wheat

dicamba, fluroxypyr, thifensulfuron-methyl, and tribenuron-methyl

Multiple Resistance: 2 Sites of Action
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
Auxin Mimics ( HRAC Group 4 (Legacy O)

Canada (Alberta)

2017

Canola, Corn (maize), Fallow, Lentils, Peas, Wheat, and Winter barley

dicamba, glyphosate, thifensulfuron-methyl, and tribenuron-methyl

Multiple Resistance: 3 Sites of Action
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)
Auxin Mimics ( HRAC Group 4 (Legacy O)

Canada (Saskatchewan)

2021

Mustard

saflufenacil

Inhibition of Protoporphyrinogen Oxidase ( HRAC Group 14 (Legacy E)

Czech Republic

1996

Railways, and Roadsides

atrazine, chlorsulfuron, imazapyr, metsulfuron-methyl, nicosulfuron, prosulfuron, rimsulfuron, sulfosulfuron, thifensulfuron-methyl, tribenuron-methyl, and triflusulfuron-methyl

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)

Spain

2022

Wheat, and Winter barley

2,4-D, glyphosate, MCPA, and thifensulfuron-methyl

United States (Kansas)

1976

Corn (maize), and Railways

atrazine

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

United States (Colorado)

1982

Corn (maize)

atrazine

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

United States (Montana)

1984

Railways

atrazine

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

United States (Wyoming)

1984

Corn (maize)

atrazine

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

United States (Iowa)

1985

Railways

atrazine

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

United States (Wisconsin)

1987

Corn (maize), and Railways

atrazine

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

United States (North Dakota)

1987

Cropland, and Wheat

chlorsulfuron, and metsulfuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Kansas)

1987

Cropland, and Wheat

chlorsulfuron

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (New Mexico)

1988

Railways, and Roadsides

sulfometuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (South Dakota)

1988

Cropland, and Wheat

chlorsulfuron

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Idaho)

1989

Roadsides, and Wheat

chlorsulfuron

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Montana)

1989

Cropland, and Wheat

chlorsulfuron, and metsulfuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Washington)

1989

Cereals, and Wheat

chlorsulfuron

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Colorado)

1989

Roadsides, and Wheat

metsulfuron-methyl, and triasulfuron

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Illinois)

1992

Cropland, and Railways

atrazine

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

United States (Oklahoma)

1992

Roadsides, and Wheat

chlorsulfuron, metsulfuron-methyl, and sulfometuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Oregon)

1993

Wheat

chlorsulfuron, metsulfuron-methyl, and triasulfuron

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Minnesota)

1994

Cropland, and Wheat

imazethapyr, thifensulfuron-methyl, and tribenuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Montana)

1994

Cropland, and Wheat

dicamba, and fluroxypyr

Auxin Mimics ( HRAC Group 4 (Legacy O)

United States (Indiana)

1995

Railways

atrazine, cyanazine, and metsulfuron-methyl

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)

United States (North Dakota)

1995

Wheat

dicamba

Auxin Mimics ( HRAC Group 4 (Legacy O)

United States (Illinois)

1995

Corn (maize), Cropland, and Wheat

atrazine, and metsulfuron-methyl

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)

United States (Wisconsin)

1995

Roadsides

sulfometuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Wyoming)

1996

Wheat

metsulfuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Idaho)

1997

Roadsides

dicamba

Auxin Mimics ( HRAC Group 4 (Legacy O)

United States (Utah)

1998

Industrial sites

sulfometuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (North Dakota)

1998

Corn (maize)

atrazine

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

United States (Texas)

1998

Wheat

metsulfuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Colorado)

1999

Corn (maize)

dicamba

Auxin Mimics ( HRAC Group 4 (Legacy O)

United States (North Dakota)

2004

Railways

diuron, metribuzin, and tebuthiuron

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

United States (Michigan)

2005

Sugar beets

imazamox, and triflusulfuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (Kansas)

2007

Corn (maize), Cotton, and Soybean

glyphosate

Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

United States (Nebraska)

2009

Corn (maize)

dicamba

Auxin Mimics ( HRAC Group 4 (Legacy O)

United States (South Dakota)

2009

Corn (maize), and Soybean

glyphosate

Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

United States (Nebraska)

2011

Corn (maize), and Soybean

glyphosate

Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

United States (North Dakota)

2012

Corn (maize), and Soybean

glyphosate

Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

United States (Montana)

2012

Cereals

glyphosate

Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

United States (Colorado)

2012

Cereals

glyphosate

Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

United States (Oklahoma)

2013

Corn (maize)

glyphosate

Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

United States (Montana)

2013

Wheat

glyphosate, metsulfuron-methyl, thifensulfuron-methyl, and tribenuron-methyl

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)

United States (Kansas)

2013

Corn (maize)

atrazine, chlorsulfuron, dicamba, and glyphosate

Multiple Resistance: 4 Sites of Action
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)
Auxin Mimics ( HRAC Group 4 (Legacy O)

United States (Kansas)

2013

Corn (maize), and Sorghum

dicamba, fluroxypyr, and glyphosate

Multiple Resistance: 2 Sites of Action
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)
Auxin Mimics ( HRAC Group 4 (Legacy O)

United States (Nebraska)

2014

Corn (maize)

atrazine

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

United States (Oregon)

2014

Corn (maize), and Sugar beets

glyphosate

Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

United States (Idaho)

2014

Corn (maize), and Sugar beets

glyphosate

Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

United States (Wyoming)

2014

Sugar beets

glyphosate

Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

Literature about Similar Cases

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Hall, L. M. ; Beckie, H. J. ; Low, R. ; Shirriff, S. W. ; Blackshaw, R. E. ; Kimmel, N. ; Neeser, C.. 2014. Survey of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) in Alberta. Canadian Journal of Plant Science 94 : 127 - 130.

Glyphosate-resistant (GR) kochia was identified in Warner county in southern Alberta in 2011. To determine the scale of the distribution and frequency of GR kochia, a randomized stratified survey of more than 300 locations (one population per location) in southern Alberta was conducted in the fall of 2012. Mature plants were collected, seed separated, and F₁ seedlings screened by spraying with glyphosate at 900 g a.e. ha^-1 under greenhouse conditions. Screening confirmed 13 GR kochia sites: seven in Warner county, five in Vulcan county, and one in Taber county. The frequency of GR individuals in a population ranged from 0.3 to 98%. GR kochia were found in arid areas where chemical fallow is a significant component of the rotation. Economic and agronomic impact of this GR weed biotype is compounded because of multiple resistance to acetolactate synthase-inhibiting herbicides..

Linda M. Hall, Hugh J. Beckie, Ryan Low, Scott W. Shirriff, Robert E. Blackshaw, Nicole Kimmel, Christoph Neeser. 2014. Survey of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) in Alberta. Can. J. Plant Sci 94 : 127 - 130.

Glyphosate-resistant (GR) kochia was identified in Warner county in southern Alberta in 2011. To determine the scale of the distribution and frequency of GR kochia, a randomized stratified survey of more than 300 locations (one population per location) in southern Alberta was conducted in the fall of 2012. Mature plants were collected, seed separated, and F1 seedlings screened by spraying with glyphosate at 900 g a.e. ha−1 under greenhouse conditions. Screening confirmed 13 GR kochia sites: seven in Warner county, five in Vulcan county, and one in Taber county. The frequency of GR individuals in a population ranged from 0.3 to 98%. GR kochia were found in arid areas where chemical fallow is a significant component of the rotation. Economic and agronomic impact of this GR weed biotype is compounded because of multiple resistance to acetolactate synthase-inhibiting herbicides..

Waite, J. ; Thompson, C. R. ; Peterson, D. E. ; Currie, R. S. ; Olson, B. L. S. ; Stahlman, P. W. ; Al-Khatib, K.. 2013. Differential kochia (Kochia scoparia) populations response to glyphosate. Weed Science 61 : 193 - 200.

Kochia is a troublesome weed throughout the western United States. Although glyphosate effectively controls kochia, poor control was observed in several no-till fields in Kansas. The objectives of this research were to evaluate kochia populations response to glyphosate and examine the mechanism that causes differential response to glyphosate. Glyphosate was applied at 0, 54, 109, 218, 435, 870, 1305, 1740, 3480, and 5220 g ae ha^-1 on 10 kochia populations. In general, kochia populations differed in their response to glyphosate. At 21 d after treatment, injury from glyphosate applied at 870 g ha^-1 range from 4 to 91%. In addition, glyphosate rate required to cause 50% visible injury (GR₅₀) ranged from 470 to 2149 g ha^-1. Differences in glyphosate absorption and translocation and kochia mineral content were not sufficient to explain differential kochia response to glyphosate..

Légère, A. ; Stevenson, F. C. ; Beckie, H. J. ; Warwick, S. I. ; Johnson, E. N. ; Hrynewich, B. ; Lozinski, C.. 2013. Growth characterization of kochia (Kochia scoparia) with substitutions at Pro₁₉₇ or Trp₅₇₄ conferring resistance to acetolactate synthase-inhibiting herbicides. Weed Science 61 : 267 - 276.

Over 90% of Canadian kochia populations are resistant to acetolactate synthase (ALS)-inhibiting herbicides. We questioned whether the target site-based resistance could affect plant growth and competitiveness. Homozygous F₂ herbicide-resistant (HR) kochia plants with an amino acid substitution at Trp₅₇₄ (sources: Alberta [AB], Saskatchewan [SK], and Manitoba [MB]), or Pro₁₉₇ (MB, AB with two populations) were grown in replacement series with homozygous F₂ herbicide-susceptible (HS) plants from the corresponding heterogeneous population (total: six populations). In pure stands, growth of HR plants from AB and SK was similar to that of HS plants, regardless of mutation; conversely, MB2-HR plants (Trp₅₇₄Leu) developed more slowly and were taller than MB2-HS plants. Final dry weight of HR plants in pure stands was similar across all six populations, whereas that for HS plants in pure stands and HR-HS plants in mixed stands (50-50%) varied with population. Results for AB and SK populations suggest little impact of either ALS mutation on kochia growth, whereas those for MB lines would suggest an unidentified factor (or factors) affecting the HS, HR, or both biotypes. The variable response within and between lines, and across HS biotypes highlights the importance of including populations of various origins and multiple susceptible controls in HR biotype studies..

Beckie, H. J. ; Blackshaw, R. E. ; Low, R. ; Hall, L. M. ; Sauder, C. A. ; Martin, S. ; Brandt, R. N. ; Shirriff, S. W.. 2013. Glyphosate- and acetolactate synthase inhibitor-resistant kochia (Kochia scoparia) in western Canada. Weed Science 61 : 310 - 318.

In summer, 2011, we investigated suspected glyphosate-resistant (GR) kochia in three chem-fallow fields (designated F1, F2, F3, each farmed by a different grower) in southern Alberta. This study characterizes glyphosate resistance in those populations, based on data from dose-response experiments. In a greenhouse experiment, the three populations exhibited a resistance factor ranging from 4 to 6 based on shoot biomass response (GR₅₀ ratios), or 5 to 7 based on survival response (LD₅₀ ratios). Similar results were found in a field dose-response experiment at Lethbridge, AB, in spring 2012 using the F2 kochia population. In fall 2011, we surveyed 46 fields within a 20-km radius of the three chem-fallow fields for GR kochia. In the greenhouse, populations were screened with glyphosate at 900 g ae ha^-1. Seven populations were confirmed as GR, the farthest site located about 13 km from the three originally confirmed populations. An additional GR population more than 100 km away was later confirmed. Populations were screened for acetolactate synthase (ALS)-inhibitor (thifensulfuron tribenuron) and dicamba resistance in the greenhouse, with molecular characterization of ALS-inhibitor resistance in the F1, F2, and F3 populations. All GR populations were resistant to the ALS-inhibiting herbicide, but susceptible to dicamba. ALS-inhibitor resistance in kochia was conferred by Pro₁₉₇, Asp₃₇₆, or Trp₅₇₄ amino acid substitutions. Based upon a simple empirical model with a parameter for selection pressure, calculated from weed relative abundance and glyphosate efficacy, and a parameter for seedbank longevity, kochia, wild oat, and green foxtail were the top three weeds, respectively, predicted at risk of selection for glyphosate resistance in the semiarid Grassland region of the Canadian prairies; wild oat, green foxtail, and cleavers species were predicted at greatest risk in the subhumid Parkland region. This study confirms the first occurrence of a GR weed in western Canada. Future research on GR kochia will include monitoring, biology and ecology, fitness, mechanism of resistance, and best management practices..

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