Shoulder season plant growth regulator programs for Poa annua control in creeping bentgrass putting greens in Tennessee

Many golf course superintendents rely on plant growth regulators (PGRs) as a primary means of managing Poa annua L. in creeping bentgrass ( Agrostis stolonifera L.), particularly the early‐stage gibberellic acid inhibitor paclobutrazol (Trimmit 2SC; Syngenta Professional Products). While herbicides for Poa annua control are often applied during fall and winter, there is limited information regarding the efficacy of shoulder season PGR applications for Poa annua control. Trials were conducted in Knoxville, TN, during 2023 and 2024, to evaluate the efficacy of prohexadione‐calcium (Anuew EZ; Cleary Chemicals) at 18 fl oz ac −1 , prohexadione‐calcium + paclobutrazol at 18 fl oz ac −1 + 5 fl oz ac −1 , trinexapac‐ethyl (Primo Maxx; Syngenta Professional Products) at 6 fl oz ac −1 , trinexapac‐ethyl + paclobutrazol at 6 fl oz ac −1 + 5 fl oz ac −1 , and paclobutrazol at 5 fl oz ac −1 . A non‐treated check was included for comparison along with the selective herbicide methiozolin (PoaCure; Moghu USA) at 0.2 gal ac −1 . PGR treatments were applied at ∼14‐day intervals during October and November and at ∼28‐day intervals thereafter. Methiozolin was applied twice in the fall of each year. Prohexadione‐calcium + paclobutrazol, trinexapac‐ethyl + paclobutrazol, and paclobutrazol alone controlled Poa annua 75%–88% by 22 weeks after initial treatment (WAIT) in 2023 and 93%–94% by 22 WAIT in 2024. Combinations of prohexadione‐calcium or trinexapac‐ethyl with paclobutrazol led to a reduction in Poa annua coverage of ≥80% compared with non‐treated check plots at 22 WAIT in 2024. Transient creeping bentgrass injury was observed yearly with paclobutrazol‐containing treatments and was likely related to overregulation from applying treatments when ≤196 growing degree days had accumulated.