Abstract
In Portugal, glyphosate is widely used for weed control on perennial crops and non-cropping areas. It is considered an herbicide of high risk of resistance worldwide. Glyphosate resistance in Portugal was recently confirmed in Conyza bonariensis populations from intensive olive groves. This paper presents the results of a survey conducted for detecting glyphosate resistance in populations of Conyza canadensis. Whole plant dose-response bioassays were conducted to confirm resistance. ED50 values ranged from 32.72 g.ha-1 in susceptible population to 77.91 g.ha-1 for the most resistant population. The resistance factor (RF = ED50R/ED50S) was around 2 for all populations. These values reflect a trend that all populations studied were resistant to glyphosate and laboratory tests to determine the mechanism of resistance are in course.
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