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 the 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, 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 showed that 0.38 and 0.50 kg ae ha-1 of glyphosate were needed to achieve 80% (ED80) control at 30 DAT, while 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 80% (ED80) 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 plus imazapic, or nicosulfuron + metsulfuron reduced guineagrass biomass while 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.

The combination of florpyrauxifen-benzyl + 2,4-D is a new, pre-packaged herbicide mixture for use in pastures and hayfields in the United States. Unlike many other pasture herbicides, florpyrauxifen-benzyl + 2,4-D is reported to preserve white clover. However, limited research exists on the efficacy of florpyrauxifen-benzyl + 2,4-D on common weed species and on the level of tolerance of white clover to it. Field trials were conducted in Virginia in 2018 to 2020 to evaluate control of various broadleaf weeds with florpyrauxifen-benzyl + 2,4-D compared to other commonly used herbicides. Field and greenhouse studies were also carried out to assess white clover tolerance. Weed species evaluated included bulbous buttercup, Canada thistle, horsenettle, and broadleaf plantain. Florpyrauxifen-benzyl + 2,4-D provided 75% to 99% control of all weeds 90 d after application except for horsenettle (56%), while causing the least white clover injury of any herbicide treatment that was evaluated. Spring herbicide applications resulted in greater bulbous buttercup control compared to fall applications, but florpyrauxifen-benzyl + 2,4-D provided greater than 81% control from both application timings. There were no differences in aboveground biomass between white clover varieties; however, all herbicides reduced white clover biomass compared to a nontreated control. This research suggests that florpyrauxifen-benzyl + 2,4-D can improve overall forage quality by controlling broadleaf weeds in mixed grass-legume stands while preserving white clover.

The tolerance of bermudagrass and stargrass to the relatively new herbicide, aminocyclopyrachlor (ACP), must be known before it can be recommended for weed control in these forage systems. Field experiments were conducted in 2012 and 2013 in south-central Florida to determine the tolerance of established bermudagrass and stargrass to various rates and combinations of ACP, chlorsulfuron, 2,4-D, triclopyr, and metsulfuron. Overall, bermudagrass and stargrass injury was transient and was minimal by 60 d after treatment (DAT). Similarly, biomass production was negatively affected at 30 DAT when treated with ACP at rates of 70 g ae ha−1 or greater, but was similar to the nontreated control by 60 DAT. Tank-mixing ACP with chlorsulfuron, 2,4-D amine, triclopyr, or metsulfuron did not increase injury compared with ACP alone applied at equivalent rates. Forage nutritive values were unaffected by herbicides. These data suggest that long-term effects of ACP on bermudagrass and stargrass are negligible, and this herbicide could be an important component of weed management programs in these forage systems.