Identification, mapping, and chemical control of fleabane resistant to glyphosate, chlorimuron, paraquat, and 2,4-D

Monitoring herbicide-resistant weeds makes it possible to study the evolution and spread of resistance, which provides important information for their management. The objective of this study was to map fleabane accessions in the states of Paraná (PR) and Mato Grosso do Sul (MS), Brazil, to identify herbicide-resistant accessions and their response to soybean preplant chemical burndown management strategies. Fleabane seeds were collected in agricultural areas in PR and MS in 2018, 2019, and 2020. Initial screening was performed for glyphosate, chlorimuron, paraquat, 2,4-D, saflufenacil, and glufosinate efficacy. Subsequently, dose-response experiments were conducted. Field experiments were carried out in three locations, where accessions of multiple herbicide–resistant Sumatran fleabane were identified. Herbicides were used in single or sequential applications at three plant heights (10 cm). After preliminary screening, accessions were classified as putative resistant (