ALS Resistant Annual Sedge Confirmed in Georgia.

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Abstract.  Acetolactate synthase (ALS) inhibitors are widely used for POST control of sedges (Cyperus spp.) 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-methyl.  The objectives of this research were to evaluate (1) the resistance levels to halosulfuron-methyl, (2) efficacy of various herbicides for control, and (3) the molecular and physiological basis for resistance.  In greenhouse experiments, the halosulfuron-methyl rate required to reduce shoot biomass 50% from the nontreated at 8 weeks after treatment (WAT) measured 8 and >1120 g ai ha^-1 for the S and R-biotype, respectively.  Imazapic, sulfosulfuron, and trifloxysulfuron-sodium reduced biomass of the S-biotype >60% at 8 WAT, but biomass was reduced ≤20% for the R-biotype.  Glufosinate, glyphosate, MSMA, and sulfentrazone reduced shoot biomass of the R-biotype by 93, 86, 97, and 45%.  In laboratory experiments, the halosulfuron-methyl concentration required to inhibit isolated ALS enzymes 50% measured 58 and >1000 mM 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.  This is also the first report of ALS-resistance in a sedge species from a turfgrass system.