Blackeyed Susan establishment and injury following application of common roadsides herbicides

Abstract Limited herbicide options are available for selective weed management in roadside native plantings. Thus, this field study evaluated blackeyed Susan's ( Rudbeckia hirta L.) tolerance to four postemergence (POST) herbicides—quinclorac, florpyrauxifen‐benzyl, clopyralid, and metsulfuron—during prairie establishment in Fayetteville, AR, across two growing seasons in 2022 and 2023. Blackeyed Susan was assessed for plant incidence, bloom count, and visible injury. In 2022, no reduction in blackeyed Susan blooms was detected in response to POST herbicides; however, peak bloom counts occurred 1 week after treatment (WAT) and ranged from 1.1 to 1.6 blooms per ft 2 . In 2023, at 10 WAT, blackeyed Susan plants were detected in 56% of nontreated plots, and selected POST herbicides greatly reduced blackeyed Susan plant densities: clopyralid (7%), florpyrauxifen‐benzyl (20%), metsulfuron (31%), quinclorac (39%). Similarly, blackeyed Susan exhibited unacceptable injury in response to POST herbicides, with each treatment causing ≥80% injury at 4 WAT in 2023. Reductions in plant stand and bloom count, in addition to the severe injury seen in blackeyed Susan, indicate that the selected POST herbicides are not a viable weed management option during the establishment of blackeyed Susan plantings.