Abstract Background: Sagittaria montevidensis Cham. & Schltdl. is a weed that forms dense infestations in wet-seeded rice. The herbicide florpyrauxifen-benzyl is widely used in rice cultivation; however, there have been reports of failed S. montevidensis control, and these cases are increasing. Objective: This study aimed to evaluate S. montevidensis for resistance the florpyrauxifen-benzyl and assess the sensitivity of this biotype to auxin-mimicking herbicides from other chemical groups. Methods: The experiments were conducted in greenhouse using a completely randomized design with four replicates. Dose-response tests were performed using two biotypes of S. montevidensis, resistant and sensitive. The experiments were performed over two generations, using increasing doses of the florpyrauxifen-benzyl. The experiment with other auxin mimics was conducted with the second-generation populations, using increasing doses of the herbicides 2,4-D, dicamba, and triclopyr. In both experiments, weed control was assessed at 7, 14, and 28 days after application (DAA), and the dry mass of the aerial part was determined at 28 DAA. Results: Resistance of S. montevidensis to florpyrauxifen-benzyl was confirmed, with a resistance factor >700 in the two evaluated generations. The biotype was sensitive to 2,4-D, dicamba, and triclopyr achieving greater than 80% control in all treatments, and cross-resistance to synthetic auxins was ruled out. Conclusions: Evolution of resistance to florpyrauxifen-benzyl by S. montevidensis seriously compromises paddy rice production, highlighting the urgent need for alternative approaches. Background Cham Schltdl wetseeded wet seeded florpyrauxifenbenzyl florpyrauxifen benzyl cultivation however S Objective auxinmimicking mimicking groups Methods replicates Doseresponse Dose response generations florpyrauxifenbenzyl. benzyl. secondgeneration second generation populations 2,4D, 24D D 2,4 D, 2 4 2,4-D dicamba 7 14 DAA, DAA , (DAA) Results confirmed 700 >70 80 treatments crossresistance cross out Conclusions production approaches 4D 2,4D 24 2, 1 (DAA 70 >7 8 >