(Cyperus difformis)

ALS inhibitors (B/2)

Smallflower Umbrella Sedge (Cyperus difformis) is a monocot weed in the Cyperaceae family.  In Italy this weed first evolved resistance to Group B/2 herbicides in 1999 and infests Rice.   Group B/2 herbicides are known as ALS inhibitors (Inhibition of Acetolactate Synthase ).  Research has shown that these particular biotypes are resistant to azimsulfuron, bensulfuron-methyl, and cinosulfuron and they may be cross-resistant to other Group B/2 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 Jun 03, 2003 )

Common NameSmallflower Umbrella Sedge
SpeciesCyperus difformis
GroupALS inhibitors (B/2)
Herbicidesazimsulfuron, bensulfuron-methyl, and cinosulfuron
Contributors - (Alphabetically)Maurizio Sattin, and Francesco Vidotto 
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Roberto Busi
Schoenoplectus mucronatus (L.) Palla and Cyperus difformis L. accessions resistant to ALS-inhibitors in Italian rice fields.

Vidotto, F; Busi, R; Ferrero, A. Dipartimento di Agronomia, Selvicoltura e Gestione del Territorio. Grugliasco, Italy.

Sulfonylureas and other ALS-inhibitor herbicides have been used in Italian paddy fields for more than 10 years. Since 1995, lack of control has been reported for Alisma plantago-aquatica L. and Schoenoplectus mucronatus (L.) Palla. Starting from 1999, insufficient efficacy of ALS-inhibitors herbicides have been reported also against Cyperus difformis L.  A dose-response study has been carried out in the greenhouse to estimate the sensitivity of different S. mucronatus and C. difformis accessions to two bensulfuron-methyl and cinosulfuron.  Two S. mucronatus (RS1 and RS2) and one C. difformis (RC1)accessions that escaped field treatments were sprayed either with bensulfuron-methyl or cinosulfuron at 8 doses, from 0 to 4x the recommended field rate (100 g a.i.ha-1 and 80 g a.i.ha-1 for bensulfuron and cinosulfuron, respectively). Two additional accessions were also included as sensitive references (SS and SC, for S. mucronatus and C. difformis, respectively). Seeds of both species were placed on 36 cm2 pots filled with commercial potting substrate. Prior to seeding, S. mucronatus seeds were scarified with sulphuric acid for 5’. Treatments were applied at 4-leaf stage. Aboveground fresh weight per pot was determined 15-20 days after spraying.   In S. mucronatus, the rate determining 50% of growth reduction (GR50) referred to bensulfuron-methyl and cinosulfuron was more than 1,000 and 100 times higher, respectively, than that of SS, both in RS1 and RS2. In C. difformis, the GR50 of RC1 referred to bensulfuron-methyl was higher than 4x. In the case of cinosulfuron, GR50 of RC1 was more than 700 times higher than that of SC.  The accessions of both species show a variable degree of resistance both to bensulfuron-methyl and cinosulfuron, which are widely used in Italian rice fields. Further investigations are needed to understand the mechanism of resistance.

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Confirmation Tests

Field, and Greenhouse trials comparing a known susceptible Smallflower Umbrella Sedge biotype with this Smallflower Umbrella Sedge biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetic studies on Group B/2 resistant Smallflower Umbrella Sedge 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 B/2 resistant Smallflower Umbrella Sedge from Italy please update the database.
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Senior Weed Scientist
Italian National Research Council (cnr)
IBAF - Weed Science Unit
Viale dell'Università 16
Legnaro, 35020, Padova
Email Maurizio Sattin
Senior Weed Scientist
Università Degli Studi Di Torino
Scienze Agrarie
Forestali e Alimentari
Largo Braccini
Grugliasco, 10095, TO
Email Francesco Vidotto


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Italy have been instrumental in providing you this information. Particular thanks is given to Maurizio Sattin, and Francesco Vidotto for providing detailed information.
Herbicide Resistant Smallflower Umbrella Sedge Globally
(Cyperus difformis)
Herbicide Resistant Smallflower Umbrella Sedge Globally
(Cyperus difformis)
Drag a column header and drop it here to group by that column
Herbicide Resistant Smallflower Umbrella Sedge Globally
(Cyperus difformis)
#CountryFirstYearSituationActive IngredientsSite of Action
1 Australia (New South Wales ) AustraliaNew South Wales 1994 Rice bensulfuron-methyl 1 ALS inhibitors (B/2)
71Cyperus difformisSmallflower Umbrella Sedge6
2 BrazilBrazil 2000 Rice cyclosulfamuron, and pyrazosulfuron-ethyl 5 ALS inhibitors (B/2)
71Cyperus difformisSmallflower Umbrella Sedge5118
3 GreeceGreece 2009 Rice azimsulfuron, and halosulfuron-methyl 19 ALS inhibitors (B/2)
71Cyperus difformisSmallflower Umbrella Sedge13051
4 ItalyItaly 1999 Rice azimsulfuron, bensulfuron-methyl, and cinosulfuron 24 ALS inhibitors (B/2)
71Cyperus difformisSmallflower Umbrella Sedge5155
5 South KoreaSouth Korea 2002 Rice azimsulfuron, bensulfuron-methyl, cinosulfuron, cyclosulfamuron, ethoxysulfuron, halosulfuron-methyl, imazosulfuron, and pyrazosulfuron-ethyl 27 ALS inhibitors (B/2)
71Cyperus difformisSmallflower Umbrella Sedge152
6 SpainSpain 2000 Rice bensulfuron-methyl, and penoxsulam 38 ALS inhibitors (B/2)
71Cyperus difformisSmallflower Umbrella Sedge5140
7 TurkeyTurkey 2010 Rice azimsulfuron, bensulfuron-methyl, bispyribac-sodium, and penoxsulam 71 ALS inhibitors (B/2)
71Cyperus difformisSmallflower Umbrella Sedge5532
8 United States (California) United StatesCalifornia1993 Rice bensulfuron-methyl 45 ALS inhibitors (B/2)
71Cyperus difformisSmallflower Umbrella Sedge391
9 United States (Arkansas) United StatesArkansas2010 Rice halosulfuron-methyl 45 ALS inhibitors (B/2)
71Cyperus difformisSmallflower Umbrella Sedge5562
10 United States (California) United StatesCalifornia2013 Rice propanil 45 PSII inhibitors - Serine 264 Binders (C2/7)
71Cyperus difformisSmallflower Umbrella Sedge6739
Literature about Similar Cases

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PERMISSION MUST BE OBTAINED FIRST if you intend to base a significant portion of a scientific paper on data derived from this site. Citation:
Heap, I.  The International Herbicide-Resistant Weed Database.  Online.  Monday, April 12, 2021 .  Available Copyright © 1993- 2021 All rights reserved. Fair use of this material is encouraged. Proper citation is requested.