First evidence of multiple resistance of Sumatran Fleabane (Conyza sumatrensis (Retz.) E.Walker) to five- mode-of-action herbicides

Abstract

Herbicide resistance is the evolutionary response of weeds to the selection pressure caused by repeated application of the same active ingredient. It can result from two different mechanisms, known as target site resistance (TSR) and non-target site resistance (NTSR). In addition to single-herbicide resistance, multiple resistance can occur due to herbicides selection or accumulation of resistance genes by cross-pollination. The aim of this research was to investigate the suspect of multiple herbicide resistance of Sumatran Fleabane (Conyza sumatrensis (Retz.) E.Walker) to herbicides frequently used as a burndown application. Dose-responses in a whole-plant assay were carried out to investigate multiple-resistance of Sumatran fleabane to paraquat, saflufenacil, diuron, 2,4-D and glyphosate. Results indicated that the resistance index (ratio R/S) based on herbicide rate to cause 50% mortality (LD50) were 25.51, 1.39, 7.29, 1.84 and 7.55 for paraquat, saflufenacil, diuron, 2,4-D and glyphosate, respectively. Based on herbicide rate required to cause a 50% reduction in plant growth (GR50), the resistant index were 51.83, 14.10, 5.05, 3.96 and 32.90 for the same herbicides, respectively. Our results confirmed multiple resistance of Conyza sumatrensis from Paraná-Brazil to herbicides from five-mode of-action. This was the first report of Conyza sumatrensis resistant to 2,4-D and the first case of Conyza sumatrensis presenting multiple resistant to herbicides from five- mode of-action in the world.