Impact of glyphosate, imazapic, and metsulfuron on bahiagrass, vaseygrass, and guineagrass control

Abstract Bahiagrass, guineagrass, and vaseygrass are dominant weeds in bermudagrass pastures. Chemical control of these weeds is difficult, as some herbicides damage bermudagrass. The objectives of this study were to assess the effect of glyphosate and glyphosate mixes with imazapic and nicosulfuron + metsulfuron on bahiagrass control and to evaluate the effect of glyphosate and/or imazapic and nicosulfuron + metsulfuron on guineagrass and vaseygrass control under greenhouse conditions. Bahiagrass field trials were conducted in Citra and Ona, FL, in 2016 and 2018, respectively, while greenhouse experiments were conducted in Ona in 2017 and 2018. Glyphosate tank mixes reduced bahiagrass biomass in Ona, whereas at Citra, biomass reduction did not differ between treatments, although visual estimates of control were lowest with glyphosate at 0.28 kg ae ha −1 . Results from the greenhouse experiment show that 0.38 and 0.50 kg ae ha −1 of glyphosate were needed to achieve 80% (ED 80 ) control at 30 d after treatment (DAT), whereas 0.60 and 0.47 kg ae ha −1 were required to reduce 80% biomass of guineagrass and vaseygrass at 60 DAT, respectively. Vaseygrass needed lower imazapic rates (0.05 and 0.19 kg ae ha −1 ) for ED 80 control (visual estimates) and biomass reduction, respectively, whereas guineagrass required higher doses (0.31 and 0.28 kg ae ha −1 for visual estimates of control and biomass reduction, respectively). Glyphosate at 0.56 kg ae ha −1 , glyphosate + imazapic, or nicosulfuron + metsulfuron reduced guineagrass biomass, whereas imazapic only, glyphosate tank mixes, and nicosulfuron + metsulfuron resulted in the highest vaseygrass biomass reduction. Glyphosate and glyphosate tank mixes were consistent in controlling all grasses, yet imazapic was effective at higher rates for guineagrass.