Identification of glyphosate resistance in Salsola tragus in Northeastern Oregon

BACKGROUND Farmers in the low-rainfall region of eastern Oregon rely on repeated applications of non-selective herbicides, predominately glyphosate, to control Salsola tragus in no-till fallow systems. Reports of poor glyphosate effectiveness have increased in recent years. Reduced efficacy is often attributed to dust, water stress, or generally poor growing conditions during application. Inadequate control also may be the result of the evolution of glyphosate resistance. Therefore, studies were undertaken to determine if glyphosate-resistant S. tragus populations occur in Oregon. RESULTS Results from dose response studies confirmed of glyphosate resistance in three of ten Oregon Salsola tragus populations. The ratio I50R/I50S from dose–response curves was on average 3.1 for the relative dry biomass per plant and 3.2 for the percent of surviving plants per pot in these three populations. Plant mortality at recommended glyphosate doses for the resistant populations was less than 30% three weeks after treatment. CONCLUSIONS Glyphosate resistance in S. tragus highlights the imperative need to diversify weed control strategies to preserve the longevity and sustainability of herbicides in semi-arid cropping systems of the Pacific Northwest.