| Summary: | The excessive use of the herbicide glyphosate on annual and perennial crops grown in Southern Spain has caused an increase in resistant weed populations. <i>Bromus rubens</i> has begun to spread through olive and almond cultivars due to low glyphosate control over these species, whereas previously it had been well controlled with field dose (1080 g ae ha<sup>−1</sup>). Characterization using Simple Sequence Repeat (SSR) markers confirmed the presence of <i>B. rubens</i> collected in Andalusia. A rapid shikimic acid accumulation screening showed 17 resistant (R) populations with values between 300 and 700 µg shikimate g<sup>−1</sup> fresh weight and three susceptible (S) populations with values between 1200 and 1700 µg shikimate g<sup>−1</sup> fresh weight. In dose–response experiments the GR<sub>50</sub> values agreed with previous results and the resistance factors (RFs: GR<sub>50</sub> R/GR<sub>50</sub> S (Br1)) were between 4.35 (Br9) and 7.61 (Br19). Foliar retention assays shown no differences in glyphosate retention in both R and S populations. The tests carried out in a resistant field (Br10) demonstrated the control efficacy of pre-emergence herbicides since flazasulfuron in the tank mix with glyphosate had up to 80% control 15 to 120 days after application (DAA) and grass weed postemergence herbicides, such as propaquizafop + glyphosate and quizalofop + glyphosate, had up to 90% control 15 to 90 DAA. Results confirm the first scientific report of glyphosate-resistant <i>B. rubens</i> worldwide; however, the use of herbicides with another mode of action (MOA) is the best tool for integrated weed management.
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