<b>HRAC Group 2</b> <font size='2'> (Legacy B) </font> resistant Cyperus esculentus from United States, Georgia

INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

HRAC GROUP 2 (LEGACY B) RESISTANT YELLOW NUTSEDGE
(Cyperus esculentus)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

United States, Georgia

INTRODUCTION		YELLOW NUTSEDGE
Yellow Nutsedge (Cyperus esculentus) is a monocot weed in the Cyperaceae family. In Georgia this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2019 and infests Peanut (groundnut). 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 imazapic 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.

QUIK STATS (last updated Mar 04, 2026 )
Common Name	Yellow Nutsedge
Species	Cyperus esculentus
Group	Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicides	imazapic
Location	United States, Georgia
Year	2019
Situation(s)	Peanut (groundnut)
Contributors - (Alphabetically)	Nicholas Basinger, Scott Mcelroy, and Eric Prostko
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NOTES ABOUT THIS BIOTYPE

GENERAL

Cite this article: Lindell HC, Prostko EP, McElroy S, Patel JD, Blankenship JD, Grey TL, Basinger NT (2025). Evaluation of ALS-resistant yellow nutsedge (Cyperus esculentus) in Georgia peanut. Weed Sci. 73(e19), 1–7. doi: 10.1017/wsc.2024.87

Evaluation of ALS-resistant yellow nutsedge (Cyperus esculentus) in Georgia peanut Hannah C. Lindell¹, Eric P. Prostko², Scott McElroy³, Jinesh D. Patel⁴, Jason D. Blankenship⁵, Timothy L. Grey⁶and Nicholas T. Basinger⁷

¹Graduate Research Assistant, Department of Crop and Soil Sciences, University of Georgia, Athens, GA, USA; ²Professor and Extension Weed Specialist, Department of Crop and Soil Sciences, University of Georgia, Tifton, GA, USA; ³Professor in Weed Science and Turf, Department of Crop, Soil and Environmental Sciences, Auburn University, Auburn, AL, USA; ⁴Research Associate, Department of Crop, Soil and Environmental Sciences, Auburn University, Auburn, AL, USA; ⁵Former Randolph County Extension Agent, University of Georgia Cooperative Extension, Cuthbert, GA, USA; ⁶Professor, Department of Crop and Soil Sciences, University of Georgia, Tifton GA, USA and ⁷Associate Professor, Department of Crop and Soil Sciences, University of Georgia, Athens, GA, USA

Abstract

Accounting for 53% of U.S. peanuts (Arachis hypogaea L.), Georgia is the top peanut-producing state, with approximately 1.42 billion kg produced in 2023. Peanut producers often use the acetolactate synthase (ALS) imidazolinone herbicide imazapic, but reduced yellow nutsedge (CyperusesculentusL.)controlwasreportedinGeorgiapeanutsafter4yrofcontinuousimazapic use. This study aimed to determine the level of resistance (LD_50,I₅₀, and GR₅₀) and potential cross-resistance for the suspected resistant population and to identify the associated genetic mutations conferring resistance. A susceptible biotype was treated with 0, 0.0088, 0.0175, 0.035, 0.07, 0.14, 0.28, and 0.56 kg ai ha⁻¹, and a resistant biotype was sprayed with 0, 0.07, 0.14, 0.28, 0.56, 1.13, 2.26, and 4.5 kg ai ha⁻¹of imazapic. To determine whether the suspected resistant biotype was cross-resistant to halosulfuron-methyl, an ALS herbicide used to control Cyperus spp.,both biotypesweretreatedwith0,0.0117, 0.0233,0.0466,0.0933,0.187,0.373,and0.746gai ha⁻¹of halosulfuron-methyl. Plants were rated for injury at 7, 14, and 28 d after treatment (DAT), and aboveground biomass was harvested at 28 DAT. For imazapic, LD₅₀was 0.041 and 1.503 kg ai ha⁻¹and the GR₅₀was estimated to be 0.0128 and 1.853 kg ha⁻¹for Sus and Res biotypes, respectively, indicating 36- and 145-fold increase in resistance of the Res biotype for I₅₀and GR₅₀, respectively. Both biotypes responded similarly to applications of halosulfuron-methyl, with biomass reduction at rates greater than 0.023 kg ai ha⁻¹. Transcriptome profiles revealed a mutation in the target-site gene of the resistant biotype causing an amino acid substitution from alanine to valine at position 205 (Ala-205-Val). Growers should continue to rotate chemistries and implement integrated weed management approaches for control of C. esculentus, as the use of imazapic over consecutive years has led to resistance in C. esculentus.

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ACADEMIC ASPECTS

Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Yellow Nutsedge biotype with this Yellow Nutsedge 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 Yellow Nutsedge 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 Yellow Nutsedge from Georgia 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 Yellow Nutsedge from Georgia please update the database.

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CONTRIBUTING WEED SCIENTISTS

NICHOLAS BASINGER

Associate Professor Ian Heap Crop and Soil Sciences CAES Campus 4105 Miller Plant Sci 120 Carlton St. Athens, 30602, Georgia United States Email Nicholas Basinger Web : Web Site Link

SCOTT MCELROY

Assistant Professor Auburn University Depart. Of Agronomy And Soils 201 Funchess Hall Auburn, 36830, Alabama United States Email Scott Mcelroy Web : Web Site Link

ERIC PROSTKO

Extension Weed Specialist University Of Georgia Agricultural and Environmental Sciences P.O. Box 478 Tifton, 31794-0748, Georgia United States Email Eric Prostko Web : Web Site Link

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Georgia have been instrumental in providing you this information. Particular thanks is given to Nicholas Basinger, Scott Mcelroy, and Eric Prostko for providing detailed information.

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Herbicide Resistant Yellow Nutsedge Globally
(Cyperus esculentus)

Country

FirstYear

Situation

Active Ingredients

Site of Action

Italy

2017

Rice

azimsulfuron, and halosulfuron-methyl

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

United States (Arkansas)

2013

Rice

halosulfuron-methyl

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

United States (Georgia)

2019

Peanut (groundnut)

imazapic

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

Literature about Similar Cases

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Tehranchian, P., J. K. Norsworthy, V. Nandula, S. McElroy, S. Chen, and R. C. Scott. 2015. First report of resistance to acetolactate-synthase-inhibiting herbicides in yellow nutsedge (Cyperus esculents): confirmation and characterization
. Pest Management Science 71 : 1274 - 1280.

BACKGROUND: Yellow nutsedge is one of the most problematic sedges in Arkansas rice, requiring the frequent use of halosulfuron (sulfonylurea) for its control. In the summer of 2012, halosulfuron at 53 g ha−1 (labeled field rate) failed to control yellow nutsedge. The level of resistance to halosulfuron was determined in the putative resistant biotype, and its cross-resistance to other acetolactate synthase (ALS) inhibitors from four different herbicide families. ALS enzyme assays and analysis of the ALS gene were used to ascertain the resistance mechanism.

RESULTS: None of the resistant plants was killed by halosulfuron at a dose of 13 568 g ha−1 (256× the field dose), indicating a high level of resistance. Based on the whole-plant bioassay, the resistant biotype was not controlled by any of the ALS-inhibiting herbicides (imazamox, imazethapyr, penoxsulam, bispyribac, pyrithiobac-sodium, bensulfuron and halosulfuron) tested at the labeled field rate. The ALS enzyme from the resistant biotype was 2540 times less responsive to halosulfuron than the susceptible biotype, and a Trp574-to-Leu substitution was detected by ALS gene sequencing using the Illumina HiSeq.

CONCLUSION: The results suggest a target-site alteration as the mechanism of resistance in yellow nutsedge, which accounts for the cross-resistance to other ALS-inhibiting herbicide families.

Macrae, A. W. ; Culpepper, A. S. ; Batts, R. B. ; Lewis, K. L.. 2008. Seeded watermelon and weed response to halosulfuron applied preemergence and postemergence. Weed Technology 22 : 86 - 90.

Managing weeds in watermelon is challenging because of the limited availability of herbicides approved for use in this crop. Field experiments on efficacy and crop tolerance were conducted to determine the potential for halosulfuron use in watermelon in Georgia and North Carolina, USA. Halosulfuron was applied PRE, early POST (EPOST; one-leaf watermelon), and late POST (LPOST; watermelon with 30-cm runners) at 26, 39, and 52 g a.i./ha. Under weed-free conditions, PRE treatments did not injure watermelon. EPOST and LPOST treatments caused 45 and 34% injury at 2 weeks after treatment, respectively, averaged over halosulfuron rate. EPOST treatments reduced watermelon fruit number and total weight by 15 and 22%, respectively, and LPOST treatments reduced total fruit weight by 12%. Halosulfuron PRE at 39 or 52 g/ha provided 94% or greater control of carpetweed (Mollugo verticillata), Palmer amaranth (Amaranthus palmeri), and smooth pigweed (Amaranthus hybridus). EPOST treatments controlled 84 and 88% of yellow nutsedge (Cyperus esculentus) and smooth pigweed, respectively, but LPOST treatments controlled less than 83% of all weed species. Sequential applications of halosulfuron at 26 g/ha PRE and 26 g/ha LPOST controlled 89 to 99% of carpetweed, coffee senna (Senna occidentalis), Palmer amaranth, smooth pigweed, and yellow nutsedge. Our data suggest growers can effectively use halosulfuron PRE in seeded watermelon. However, POST applications should be made only after watermelon has 30 cm runners and as a salvage spot treatment where previous weed control strategies have failed to provide adequate control..

Clewis, S. B. ; Wilcut, J. W. ; Porterfield, D.. 2006. Weed management with S-metolachlor and glyphosate mixtures in glyphosate-resistant strip- and conventional-tillage cotton (Gossypium hirsutum L.). Weed Technology 20 : 232 - 241.

Field studies were conducted at Clayton, Rocky Mount and Lewiston-Woodville, North Carolina, USA, in 2001 and 2002, to evaluate weed management, crop tolerance and yield in strip- and conventional-tillage glyphosate-resistant cotton. Cotton was treated with 2 glyphosate formulations, i.e. glyphosate-IP (isopropylamine salt) or glyphosate-TM (trimethylsulfonium salt) at early postemergence (EPOST) alone or in a mixture with S-metolachlor. Early season cotton injury was minimal (3%) with either glyphosate formulation alone or in mixture with S-metolachlor. Weed control and cotton yields were similar for both glyphosate formulations. The addition of S-metolachlor to either glyphosate formulation increased control of broadleaf signalgrass (Urochloa platyphylla), goosegrass (Eleusine indica), large crabgrass (Digitaria sanguinalis) and yellow foxtail (Setaria pumila) at 14 to 43% compared to the control by glyphosate alone. S-metolachlor was not beneficial for late-season control of entire leaf morningglory (Pharbitis hederacea), jimsonweed (Datura stramonium), pitted morningglory (Ipomoea lacunosa) or yellow nutsedge (Cyperus esculentus). The addition of S-metolachlor to either glyphosate formulation increased control of common lambsquarters (Chenopodium album), common ragweed (Ambrosia artemisiifolia), Palmer amaranth (Amaranthus palmeri), smooth pigweed (Amaranthus hybridus) and velvet leaf (Abutilon theophrasti) at 6 to 46%. The addition of a late postemergence-directed (LAYBY) treatment of prometryn plus MSMA increased control to greater than 95% for all weed species regardless of EPOST treatment, and control was similar with or without S-metolachlor EPOST. Cotton lint yield was increased 220 kg/ha with the addition of S-metolachlor to either glyphosate formulation compared to yield from glyphosate alone. The addition of the LAYBY treatment increased yields by 250 and 380 kg/ha for glyphosate plus S-metolachlor and glyphosate systems, respectively. S-metolachlor residual activity allowed for an extended window for more effective LAYBY application to smaller weed seedlings instead of weeds that were possibly larger and harder to control..

Richardson, R. J. ; Zandstra, B. H.. 2006. Evaluation of flumioxazin and other herbicides for weed control in gladiolus. Weed Technology 20 : 394 - 398.

Two studies were conducted near Bronson, Michigan, USA, to determine gladiolus (Gladiolus sp.) tolerance and weed control with flumioxazin and other herbicide treatments. The first study was conducted in 2002, 2003 and 2004 to evaluate weed control and gladiolus injury with flumioxazin and 14 other pre-emergence treatments. Crop injury over the 3-year period was less than 6% and was considered commercially acceptable with flumioxazin, linuron, oryzalin, pendimethalin, prometryn, S-metolachlor and sulfentrazone. Gladiolus stand count, height, and flower count were similar to those of the nontreated control with these treatments. Clomazone, halosulfuron, imazamox, imazapic, mesotrione, oxyfluorfen, rimsulfuron, and trifloxysulfuron resulted in unacceptable crop injury. Of the acceptable treatments, only flumioxazin controlled (at least 68%) common ragweed (Ambrosia artemisiifolia), yellow nutsedge (Cyperus esculentus) and foxtail species (Setaria faberi and S. viridis var. robusta-purpurea). The second study was conducted in 2003 and 2004. Flumioxazin was evaluated at 4 rates, in mixtures with S-metolachlor and oryzalin, and in comparison with isoxaben plus oryzalin. Gladiolus injury did not exceed 6%. Common ragweed, annual grass (Digitaria sanguinalis and Eragrostis cilianensis), and yellow nutsedge control were at least 63% with all flumioxazin treatments..

Norsworthy, J. K. ; Meehan, J. T., IV. 2005. Use of isothiocyanates for suppression of Palmer amaranth (Amaranthus palmeri), pitted morningglory (Ipomoea lacunosa), and yellow nutsedge (Cyperus esculentus). Weed Science 53 : 884 - 890.

A greenhouse experiment was conducted to evaluate the herbicidal activity of five aliphatic (ethyl, propyl, butyl, allyl, and 3-methylthiopropyl) and three aromatic (phenyl, benzyl, and 2-phenylethyl) isothiocyanates (ITCs) on Palmer amaranth (A. palmeri), pitted morningglory (I. lacunosa) and yellow nutsedge (C. esculentus). All ITCs were applied to soil at 0, 10, 100, 1000 and 10 000 nmol g^-1 of soil and incorporated. All ITCs had a deleterious effect on Palmer amaranth and pitted morningglory emergence. LC₅₀ values for Palmer amaranth emergence inhibition from aliphatic and aromatic ITCs ranged from a low of 32 nmol g^-1 of soil for phenyl ITC to a high of 941 nmol g^-1 of soil for propyl ITC. Pitted morningglory was slightly more tolerant than Palmer amaranth to each of the ITCs, with LC₅₀ values for emergence ranging from 347 to 2855 nmol g^-1 of soil for 3-methylthiopropyl and butyl ITC, respectively. Yellow nutsedge was the most tolerant of the three species, with LC₅₀ values for ethyl, butyl, benzyl, and 2-phenylethyl being greater than the highest concentration of 10 000 nmol g^-1 of soil. Phenyl and 3-methylthiopropyl at 10 000 nmol g^-1 of soil were the most effective ITCs against yellow nutsedge, reducing emergence by 92%. Effectiveness of the ITCs varied across structure and species, but 3-methylthiopropyl and phenyl ITC were generally the most efficacious for the three species..

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