The objective of this study was to determine the efficacy of this herbicide in two populations of Conyza bonariensis, one suspected of resistance (B8) and a susceptible one (C), from olive groves and citrus orchards in Alentejo, south of Portugal. Assays were performed on germination agar medium, glyphosate dose-response assays in petri dishes with different concentrations of glyphosate and a greenhouse (1) and laboratory (2) study were conducted (1) to confirm and characterize glyphosate resistance and (2) to determine whether resistant and susceptible populations have differential shikimate accumulation. Population B8 showed significant higher germination and emergence than population C but lower mortality rate. Dose–response studies revealed that the suspected resistant population was two- to three-fold less sensitive to glyphosate than the susceptible population. The dose-response flazasulfuron assay with whole plant in the rosette stage revealed the doses were completely effective on both populations. Shikimate accumulation was higher in resistant population at 72-h after treatment, for the recommended concentration of glyphosate. However, it was lower for concentrations of 360 g ha-1. These results pointed that population B8 is resistant to glyphosate and flazasulfuron is an option for the chemical control of resistant populations.

Mestrado em Engenharia Agronómica - Protecção das Plantas - Instituto Superior de Agronomia