Monitoring of Herbicide-Resistant Erigeron spp. and In-Depth Assessment of the Rapid Necrosis Mechanism

This study aimed to identify and map populations of herbicide-resistant fleabane (Erigeron spp.) and to determine the mechanism of resistance involving rapid necrosis after the application of synthetic auxins. Seeds were collected from 60 fleabane accessions from Paraná (PR) and Mato Grosso do Sul (MS) states, Brazil. Diquat, glufosinate, saflufenacil, glyphosate, 2,4-D, triclopyr, and dicamba were applied. Weed control was assessed 28 days after application (DAA), with accessions showing less than 80% control being considered possibly resistant. For synthetic auxins, control was also assessed at 24 h after application (HAA) to check for rapid necrosis, which confirmed for accessions with greater than 15% control. The dose-response curve showed an accession, identified as Sumatran fleabane (Erigeron sumatrensis) and collected in PR, with multiple resistance to 2,4-D (C50 of 1986.6 g ai ha-1, RF of 2.8) and diquat (C50 of 518.3 g ai ha-1, RF of 12.4). Glyphosate resistance was found in all Erigeron spp. accessions, except for one (B24). For diquat, 28 accessions were classified as resistant. None of the accessions were classified as resistant to glufosinate and saflufenacil. Rapid necrosis was observed in 44 Erigeron spp. accessions after 2,4-D application in both states, indicating the presence of a resistance mechanism. No rapid necrosis was verified for dicamba and triclopyr or any indication of resistance.