HRAC GROUP 2 (LEGACY B) RESISTANT RICEFIELD BULRUSH
(Schoenoplectus mucronatus (=Scirpus mucronatus))

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

United States, California

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INTRODUCTION RICEFIELD BULRUSH Ricefield Bulrush (Schoenoplectus mucronatus (=Scirpus mucronatus)) is a monocot weed in the Cyperaceae family.  In California this weed first evolved resistance to Group 2 (Legacy B) herbicides in 1997 and infests Rice.   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 bensulfuron-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.

QUIK STATS (last updated Sep 15, 2000 ) Common Name Ricefield Bulrush Species Schoenoplectus mucronatus (=Scirpus mucronatus) Group Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B) Herbicides bensulfuron-methyl Location United States, California Year 1997 Situation(s) Rice Contributors - (Alphabetically) Jim Hill  Edit this Case  |  Add New Case of Resistance  |  Add Note

ACADEMIC ASPECTS Confirmation Tests Field, and Greenhouse trials comparing a known susceptible Ricefield Bulrush biotype with this Ricefield Bulrush 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 Ricefield Bulrush 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 Group 2 (Legacy B) resistant Ricefield Bulrush from California please update the database.   Edit Case  |  Add Note  |  Add Article  |  Add New Case  |  Help

CONTRIBUTING WEED SCIENTISTS JIM HILL CE Specialist University Of California Agriculture and Natural Resources One Shields Avenue 177 Hunt Hall Davis, 95616, California United States Email Jim Hill Web   : Web Site Link

ACKNOWLEDGEMENTS The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in California have been instrumental in providing you this information. Particular thanks is given to Jim Hill for providing detailed information.

Herbicide Resistant Ricefield Bulrush Globally (Schoenoplectus mucronatus (=Scirpus mucronatus)) Herbicide Resistant Ricefield Bulrush Globally (Schoenoplectus mucronatus (=Scirpus mucronatus)) Drag a column header and drop it here to group by that column Herbicide Resistant Ricefield Bulrush Globally (Schoenoplectus mucronatus (=Scirpus mucronatus)) # Country Country StateName FirstYear Situation Active Ingredients CountryID Site of Action WeedID Species CommonName ResistID 1 Chile Chile   2005 Rice bensulfuron-methyl, bispyribac-sodium, cyclosulfamuron, ethoxysulfuron, imazamox, and pyrazosulfuron-ethyl 8 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B) 182 Schoenoplectus mucronatus (=Scirpus mucronatus) Ricefield Bulrush 5396 2 Italy Italy   1995 Rice azimsulfuron, bensulfuron-methyl, cinosulfuron, and ethoxysulfuron 24 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B) 182 Schoenoplectus mucronatus (=Scirpus mucronatus) Ricefield Bulrush 1129 3 United States (California) United States California 1997 Rice bensulfuron-methyl 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B) 182 Schoenoplectus mucronatus (=Scirpus mucronatus) Ricefield Bulrush 1099 4 United States (California) United States California 2014 Rice propanil 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2) 182 Schoenoplectus mucronatus (=Scirpus mucronatus) Ricefield Bulrush 9924

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Scarabel, L. ; Locascio, A. ; Furini, A. ; Sattin, M. ; Varotto, S.. 2010. Characterisation of ALS genes in the polyploid species Schoenoplectus mucronatus and implications for resistance management. Pest Management Science 66 : 337 - 344.

BACKGROUND: The polyploid weed Schoenoplectus mucronatus (L.) Palla has evolved target-site resistance to ALS-inhibiting herbicides in Italian rice crops. Molecular and genetic characterisation of the resistance mechanism is relevant to the evolution and management of herbicide resistance. The authors aimed (a) to study the organisation of the target-site loci in two field-selected S. mucronatus populations with different cross-resistance patterns, (b) to identify the mutations endowing resistance to ALS inhibitors and determine the role of these mutations by using transgenesis and (c) to analyse the implications for the management of the S. mucronatus populations. RESULTS: Two complete ALS genes (ALS1 and ALS2) having an intron and a third partial intronless ALS gene (ALS3) were identified. The presence of multiple ALS genes was confirmed by Southern blot analyses, and ALS loci were characterised by examining cytosine methylation. In S. mucronatus leaves, the transcripts of ALS1, ALS2 and ALS3 were detected. Two mutations endowing resistance (Pro₁₉₇ to His and Trp₅₇₄ to Leu) were found in both resistant populations, but at different frequencies. Tobacco plants transformed with the two resistant alleles indicated that the Pro₁₉₇-to-His substitution conferred resistance to SU and TP herbicides, while the allele with the Trp₅₇₄-to-Leu substitution conferred cross-resistance to SU, TP, IMI and PTB herbicides. CONCLUSION: Schoenoplectus mucronatus has multiple ALS genes characterised by methylated sites that can influence the expression profile. The two mutated alleles proved to be responsible for ALS resistance. At population level, the resistance pattern depends on the frequency of various resistant genotypes, and this influences the efficacy of various ALS-inhibiting herbicides..

Tabacchi M, Scarabel L, Sattin M. 2004. Herbicide Resistance in Italian Rice Crops: A Late-Developing but Fast-Evolving Story. Med Rice Conference, Torino - Italy. 13th to 15th February 2004 : .

Herbicides have been used intensively in Italian rice crops for the last 40 years. Use of ALS-inhibitors began in 1988 and now more than 80% of rice fields are treated with these herbicides. Since 1994, three species (Alisma plantago-aquatica, Schoenoplectus mucronatus and Cyperus difformis) have evolved resistance to ALS inhibitors, while three populations of Echinochloa crus-galli have evolved resistance to propanil. A population of Echinochloa erecta recently proved to be multiple-resistant to quinclorac and propanil. It is estimated that resistance exists in more than 25,000 ha, with S. mucronatus and C. difformis showing the highest rate of increase. Field histories show that high selection pressure had been imposed for several years prior to resistance development, as well as a lack of any resistance prevention strategy. Most ALS-resistant populations show a wide pattern of cross-resistance with a high level of resistance to SU and a lower level to the TP metosulam.

Sattin, M. ; Zanin, G.. 2003. The situation of herbicide resistant weeds in Italy. Informatore Fitopatologico 53 : 24 - 27.

In Italy, 12 weed species (Amaranthus cruentus, Solanum nigrum, Chenopodium album, Avena sterilis subsp. ludoviciana, Alisma plantago-aquatica, Schoenoplectus mucronatus, Lolium spp., Papaver rhoeas, Phalaris paradoxa, Amaranthus retroflexus, Cyperus difformis and Echinochloa crus-galli) have evolved populations resistant to herbicides, although to date, the areas involved are quite limited. The cropping systems where resistance has developed are mainly monocultures (e.g. rice and durum wheat) or where short crop rotations are used. The herbicides involved are acetyl-CoA carboxylase inhibitors, acetolactate synthase inhibitors and PSII inhibitors. A brief history of herbicide resistance in Italy is presented and the major resistance management techniques for preventing its appearance and spread are outlined. Integrated weed management appears to be the best solution..

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