Multiple resistant Cyperus iria from Dominican Republic

INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

MULTIPLE RESISTANT RICE FLATSEDGE
(Cyperus iria)

Multiple Resistance: 3 Sites of Action
Inhibition of Acetyl CoA Carboxylase HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)

Dominican Republic, Northwest and North-Central

INTRODUCTION		RICE FLATSEDGE
Rice Flatsedge (Cyperus iria) is a monocot weed in the Cyperaceae family. In Dominican Republic this weed first evolved multiple resistance (to 3 herbicide sites of action) in 2024 and infests Rice. Multiple resistance has evolved to herbicides in the Groups 1 (Legacy A), Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B), and PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2). These particular biotypes are known to have resistance to bispyribac-sodium, cyhalofop-butyl, diclofop-methyl, imazamox, penoxsulam, and propanil and they may be cross-resistant to other herbicides in the Groups 1 (Legacy A), Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B), and PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2). 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 Apr 18, 2026 )
Common Name	Rice Flatsedge
Species	Cyperus iria
Group	Inhibition of Acetyl CoA Carboxylase HRAC Group 1 (Legacy A) Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B) PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
Herbicides	bispyribac-sodium, cyhalofop-butyl, diclofop-methyl, imazamox, penoxsulam, and propanil
Location	Dominican Republic, Northwest and North-Central
Year	2024
Situation(s)	Rice
Contributors - (Alphabetically)	Ricardo Alcántara-de la Cruz, Hugo Cruz-Hipólito, Rafael De Prado, Candelario Palma-Bautista, Antonia-Maria Rojano-Delgado, and Jesus Ma. Rosario Soccorro
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ACADEMIC ASPECTS

Confirmation Tests

Greenhouse trials comparing a known susceptible Rice Flatsedge biotype with this Rice Flatsedge 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 1, 2, 5 resistant Rice Flatsedge 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 multiple resistant Rice Flatsedge from Dominican Republic please update the database.

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CONTRIBUTING WEED SCIENTISTS

RICARDO ALCÁNTARA-DE LA CRUZ

Dr. Universidad de Cordoba Departamento de Quimica Agricola y Edafologia Ctra. Madrid-Cádiz Km. 396 Cordoba, 14071, Andalucia Spain Email Ricardo Alcántara-de la Cruz

HUGO CRUZ-HIPÓLITO

Research Asociate Universidad De Córdoba Química Agrícola Y Edafología Campus Universitario De Rabanales Edif. C-3 3ª Planta Córdoba, 14002, Andalucia Spain Email Hugo Cruz-Hipólito

RAFAEL DE PRADO

Research Asociate Universidad De Cordoba Qvimica Agricola Y Edafologa E T S Ingenieros Agronomos PO Box 119 Cordoba, E-14080, Andalusia Spain Email Rafael De Prado

CANDELARIO PALMA-BAUTISTA

Investigador Posdoctoral Universidad Autónoma Chapingo Departamento de Parasitología Agrícola Campus Central Carretera México – Texcoco Km 38.5 Texcoco, México CP 56230 Texcoco, 56230, Estado de México Mexico Email Candelario Palma-Bautista

ANTONIA-MARIA ROJANO-DELGADO

Researcher University of Cordoba Departamento de Parasitología Agrícola Campus of Rabanales Ctra. Nacional IV - Km 396. C-3, Edif. Marie Curie, 3º floor. Cordoba, 14071, Cordoba Spain Email Antonia-Maria Rojano-Delgado

JESUS MA. ROSARIO SOCCORRO

Associate Researcher Córdoba University Agricultural Chemistry And Edafology Campus De Rabanales Córdoba, 14071, Andalucía Region Spain Email Jesus Ma. Rosario Soccorro

ACKNOWLEDGEMENTS

The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Dominican Republic have been instrumental in providing you this information. Particular thanks is given to Ricardo Alcántara-de la Cruz, Hugo Cruz-Hipólito, Rafael De Prado, Candelario Palma-Bautista, Antonia-Maria Rojano-Delgado, and Jesus Ma. Rosario Soccorro for providing detailed information.

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Herbicide Resistant Rice Flatsedge Globally
(Cyperus iria)

Country

FirstYear

Situation

Active Ingredients

Site of Action

Brazil

2014

Rice

bispyribac-sodium, imazapic, imazethapyr, penoxsulam, and pyrazosulfuron-ethyl

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

Dominican Republic

2024

Rice

bispyribac-sodium, cyhalofop-butyl, diclofop-methyl, imazamox, penoxsulam, and propanil

Multiple Resistance: 3 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)

United States (Arkansas)

2010

Rice

bispyribac-sodium, halosulfuron-methyl, imazamox, imazethapyr, and penoxsulam

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

United States (Louisiana)

2013

Rice

halosulfuron-methyl

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

Venezuela

2015

Rice

pyrazosulfuron-ethyl

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

Literature about Similar Cases

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Riar, D. S., P. Tehranchian, J. K. Norsworthy, V. Nandula, S. McElroy, V. Srivastava, S. Chen, J. A. Bond, and R. C. Scott. 2015. Acetolactate synthase–inhibiting, herbicide-resistant Rice flatsedge (Cyperus iria): cross-resistance and molecular mechanism of resistance.. Weed Science 63 : 748 - 757.

Overuse of acetolactate synthase (ALS)–inhibiting herbicides in rice has led to the evolution of halosulfuron-resistant rice flatsedge in Arkansas and Mississippi. Resistant accessions were cross-resistant to labeled field rates of ALS-inhibiting herbicides from four different families, in comparison to a susceptible (SUS) biotype. Resistance index of Arkansas and Mississippi accessions based on an R/S ratio of the lethal dose required for 50% plant mortality (LD₅₀) to bispyribac-sodium, halosulfuron, imazamox, and penoxsulam was ≥ 21-fold. Control of Arkansas, Mississippi, and SUS accessions with labeled field rates of 2,4-D, bentazon, and propanil was ≥ 93%. An enzyme assay revealed that an R/S ratio for 50% inhibition (I₅₀) of ALS for halosulfuron was 2,600 and 200 in Arkansas and Mississippi, respectively. Malathion studies did not reveal enhanced herbicide metabolism in resistant plants. The ALS enzyme assay and cross-resistance studies point toward altered a target site as the potential mechanism of resistance. Trp₅₇₄–Leu amino acid substitution within the ALS gene was found in both Arkansas and Mississippi rice flatsedge accessions using the Illumina HiSeq platform, which corresponds to the mechanism of resistance found in many weed species. Field-rate applications of 2,4-D, bentazon, and propanil can be used to control these ALS-resistant rice flatsedge accessions..

Lanclos, D. Y. ; Webster, E. P. ; Zhang, W.. 2002. Glufosinate tank-mix combinations in glufosinate-resistant rice (Oryza sativa). Weed Technology 16 : 659 - 663.

At 14 days after treatment (DAT), glufosinate at 0.42 kg ai/ha controlled barnyard grass (Echinochloa crus-galli) and broadleaf signalgrass (Brachiaria platyphylla) 85 and 86%, respectively, in Louisiana, USA, during 1998 and 1999. Antagonism occurred for barnyard grass control with all mixtures of glufosinate at 0.42 kg/ha. At 14 DAT, no herbicide was superior to glufosinate at either rate when applied in mixture for the control of broadleaf signalgrass. Rice flatsedge (Cyperus iria) control 7 DAT was 68 and 82% with glufosinate at 0.42 and 0.84 kg/ha alone, respectively. The addition of propanil and triclopyr enhanced rice flatsedge control over that with glufosinate alone at 0.42 or 0.84 kg/ha. At 7 DAT, all herbicide mixtures increased spreading dayflower (Commelina diffusa) control compared with a single treatment of glufosinate at 0.42 kg/ha. By 28 DAT, spreading dayflower control was less than 80% with all treatments. Rice (cultivars BNGL HC-11 and BNGL-62) injury was less than 15% with all treatments..

Burgos, N. R. ; Anders, M. ; Oliver, L. R. ; Wheeler, C. C. ; Payne, S. ; Mobley, M. S.. 2000. Weed shift in cropping systems involving transgenic cultivars. Research Series - Arkansas Agricultural Experiment Station : 60 - 65.

The adoption of herbicide-resistant crops may foster the continuous use or multiple applications of one herbicide and may favour the proliferation of weed species that are more difficult to control. A study was initiated in 1999 at the Rice Research and Extension Centner, Stuttgart, Germany, to assess the change in weed composition in response to a weed control program for herbicide-resistant crops and various crop rotation schemes. Glufosinate-resistant or Liberty Link (LL) cultivars of rice and soyabean were used. Dominant weed species, before postemergence herbicide application, were Sida spinosa (prickly sida), Echinochloa crus-galli (barnyardgrass), Cyperus iria (rice flatsedge), Sesbania exaltata (hemp sesbania), Amaranthus palmeri (Palmer amaranth), Mollugo verticillata (carpetweed), and Portulaca oleracea (common purslane). Visual ratings 50 days after planting showed >90% control of all weeds in nontransgenic rice. Glufosinate (Liberty) provided excellent weed control except for barnyardgrass in LL rice (74%). For LL soyabean, glufosinate did not provide sufficient control of prickly sida (65%) and had escapes of barnyardgrass and Palmer amaranth. The conventional herbicide program for soyabean provided excellent control of prickly sida (95%) but was poor on Palmer amaranth (39%). Differential weed tolerance to glufosinate was apparent. Nontransgenic rice yielded 5947 kg/ha; the transgenic rice yielded 14% less. There was no significant difference in yield between transgenic and nontransgenic soyabean..

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