03745naa a2200289 a 450000100080000000500110000800800410001902200140006002400340007410000190010824502030012726000090033050009290033952018640126865300190313265300400315165300200319165300190321165300250323065300180325565300100327370000170328370000150330070000160331570000150333177301090334610644802024-02-28       2024    bl uuuu     u00u1 u    #d  a2073-43957 a10.3390/agronomy140100792DOI1 aKASPARY, T. E.  aConyza bonariensis' resistance to glyphosate, diclosulam, and chlorimuronbconfirmation and alternative control for the first case of multiple and cross-resistance in Uruguay.h[electronic resource]  c2024  aArticle history: Submission received 15 November 2023; Revised 25 December 2023; Accepted 26 December 2023; Published: 28 December 2023. -- Correspondence: Kaspary, T.E.;  National Agricultural Research Institute of Uruguay (INIA), La Estanzuela, Colonia, Uruguay; email:tkaspary@inia.org.uy -- Academic Editor: Shouhui Wei. -- Funding: This research was funded by Fondo Vaz Ferreira (Ministerio de Educación y Cultura-Uruguay)-Project identification: FVF/2021/013 and the National Agricultural Research Institute of Uruguay-INIA. -- This article belongs to the Topic Weed Resistance to Herbicides: Assessing and Finding Solutions for a Complex Problem (https://www.mdpi.com/topics/weed_resistance ). -- Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). --  aABSTRACT.- Conyza bonariensis L. (hairy fleabane) is a significant weed in production systems, especially due to its evolving resistance to various herbicides. In Uruguay, control failures of C. bonariensis have been reported following the use of glyphosate and ALS inhibitors. The objective of this study was to investigate the occurrence of the multiple and cross-resistance of C. bonariensis to glyphosate, chlorimuron, and diclosulam, and to assess the efficacy of alternative herbicides against these resistant biotypes. Seeds were collected from sites where plants had survived herbicide applications during the 2019/2020 and 2020/2021 seasons. Following initial screenings, biotypes were selected to establish independent dose-response curves for glyphosate, diclosulam, and chlorimuron. For each herbicide, four biotypes of C. bonariensis were tested: one susceptible (S), two putatively moderately resistant (MR) biotypes, and one putatively highly resistant (R) biotype. In each assay, eight herbicide doses were used (1/32; 1/16; 1/8; 1/2; 1; 2; and 4X for S and MR biotypes, and 1/8; 1/2; 1; 2; 4; 8; and 16X for R biotypes) based on the recommended dose (1x) for each herbicide, with four repetitions per treatment. Each assay was completely replicated twice. Resistance was confirmed through testing in two plant generations (G1 and G2). The findings reveal high levels of multiple and cross-resistance in C. bonariensis to glyphosate, diclosulam, and chlorimuron. In general, herbicides with alternative action mechanisms effectively controlled C. bonariensis exhibiting multiple and cross-resistance. This study confirms the first case of C. bonariensis cross-resistance to diclosulam and chlorimuron, and the first occurrence of multiple and cross-resistance to glyphosate, diclosulam, and chlorimuron in this species. © 2023 by the authors.  aALS inhibitors  aÁREA DE PASTURAS Y FORRAJES - INIA  aEPSPS inhibitor  aHairy fleabane  aHerbicide resistance  aSouth America  aWeeds1 aWALLER, M.E.1 aGARCIA, A.1 aCABRERA, M.1 aHILL, S.M.  tAgronomy. 2024, Volume 14, Issue 1, Article 79. https://doi.org/10.3390/agronomy14010079 -- OPEN ACCESS.