International Survey of Herbicide-Resistant Weeds

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(Cyperus compressus)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

United States, Alabama
Annual Sedge (Cyperus compressus) is a monocot weed in the Cyperaceae family.  In Alabama this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2015 and infests Turf.   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 halosulfuron-methyl, imazapic, sulfometuron-methyl, and trifloxysulfuron-Na 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.

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QUIK STATS (last updated Jan 14, 2016 )

Common NameAnnual Sedge
SpeciesCyperus compressus
GroupInhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicideshalosulfuron-methyl, imazapic, sulfometuron-methyl, and trifloxysulfuron-Na
LocationUnited States, Alabama
Contributors - (Alphabetically)Scott Mcelroy 
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Scott Mcelroy

Patrick E. McCullough, Jialin Yu, J. Scott McElroy, S. Chen, H. Zhang, Timothy L. Grey, and Mark A. Czarnota (2016) ALS–Resistant Annual Sedge (Cyperus compressus) Confirmed in Turfgrass. Weed Science: January-March 2016, Vol. 64, No. 1, pp. 33-41.

Acetolactate synthase (ALS) inhibitors are widely used for POST control of sedges in turfgrass. A suspected resistant (R) biotype of annual sedge was collected from a bermudagrass turf in Georgia with a history of exclusive use of halosulfuron. Research was conducted to evaluate the resistance level of this biotype to halosulfuron, efficacy of ALS-inhibiting herbicides and other mechanisms of action for control, and the molecular and physiological basis for resistance. In greenhouse experiments, the halosulfuron rate required to reduce shoot biomass 50% in comparison with the nontreated at 8 wk after treatment (WAT) were 8 and > 1,120 g ai ha−1 for the S (susceptible) and R biotypes, respectively. Imazapic, sulfosulfuron, and trifloxysulfuron reduced biomass of the S biotype greater than 60% at 8 WAT, but biomass was reduced less than 20% for the R biotype. Glufosinate, glyphosate, MSMA, and sulfentrazone reduced shoot biomass of the R biotype by 93, 86, 97, and 45%, respectively. In laboratory experiments, the halosulfuron concentration required to inhibit ALS activity by 50% in excised leaf tissues was 5.8 and > 1,000 μM for the S and R biotypes, respectively. Gene sequencing of the R biotype revealed a Pro-197-Ser substitution that confers resistance to ALS inhibitors. This is the first report of ALS-inhibitor resistance in annual sedge and herbicide resistance in a sedge species from a turfgrass system.

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Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Annual Sedge biotype with this Annual 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 HRAC Group 2 resistant Annual 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

Studies on the mechanism of resistance of Group 2 (Legacy B) resistant Annual Sedge from Alabama 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 Annual Sedge from Alabama please update the database.
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Assistant Professor
Auburn University
Depart. Of Agronomy And Soils
201 Funchess Hall
Auburn, 36830, Alabama
United States
Email Scott Mcelroy
Web   : Web Site Link


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Alabama have been instrumental in providing you this information. Particular thanks is given to Scott Mcelroy for providing detailed information.
Herbicide Resistant Annual Sedge Globally
(Cyperus compressus)
Herbicide Resistant Annual Sedge Globally
(Cyperus compressus)
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Herbicide Resistant Annual Sedge Globally
(Cyperus compressus)
#CountryFirstYearSituationActive IngredientsSite of Action
1 United States (Alabama) United StatesAlabama2015 Turf halosulfuron-methyl, imazapic, sulfometuron-methyl, and trifloxysulfuron-Na 45 Inhibition of Acetolactate Synthase (B/2)
329Cyperus compressusAnnual Sedge11012
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