Abstract
Conyza sumatrensis was reported to be associated with 20 cases of herbicide resistance worldwide, with a recent report of multiple drug resistance to paraquat, glyphosate, and chlorimuron in Brazil. In Paraguay, there were no reports of cases of resistance for this species; however, in 2017, researchers began identifying biotypes with resistance to paraquat, glyphosate, and chlorimuron, which is the focus of the present study. The goal of this study was to investigate the case of multiple resistance of C. sumatrensis to paraquat, glyphosate, and chlorimuron and to monitor the resistant biotypes in the departments of Canindeyú and Alto Paraná. Seeds were collected from sites where plants survived after herbicide application in the 2017/18 and 2018/19 seasons. After screening, biotypes were selected for the construction of dose–response curves. A resistance factor (RF) of 6.79 was observed for 50% control (C50) and 3.92 for 50% growth reduction (GR50) for the application of paraquat. An RF of 12.32 was found for C50 and 4.15 for GR50 for the application of glyphosate. For the application of chlorimuron, an RF of 11.32 was found for C50 and 10.96 for GR50. This confirms the multiple resistance of the C. sumatrensis biotype to paraquat, glyphosate, and chlorimuron. Population monitoring indicated the presence of C. sumatrensis with multiple resistance in departments of Canindeyú and Alto Paraná, Paraguay.
Highlights
The selection of herbicide-resistant weed biotypes is one of the major problems in agriculture today
Seeds were collected in sites where C. sumatrensis plants survived after herbicide burndown application in pre-sowing in the 2017/18 and 2018/19 growing seasons, in 33 agricultural areas located in the departments of Canindeyú and Alto Paraná, Paraguay
100% control of C. sumatrensis plants was found with the application of saflufenacil and glufosinate; for 2,4-D, the results were close to 100%
Summary
The selection of herbicide-resistant weed biotypes is one of the major problems in agriculture today. Cronquist) and Sumatran fleabane (Conyza sumatrensis (Retz.) E. There are currently 105 herbicide-resistance cases for the three Conyza spp., which includes resistance to 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) inhibitors, acetolactate synthase (ALS) inhibitors, synthetic auxins, and photosystem I inhibitors, among others [1]
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