Long‐term influence of nitrogen, plant growth regulators, and iron sulfate on annual bluegrass populations and turfgrass quality on a golf green

Annual bluegrass (ABG, Poa annua L.) is often considered an undesirable species on golf courses in many regions of the United States. However, the long‐term effect of the cultural and chemical management practices of ABG control is not sufficiently investigated. The objective of this study was to determine the long‐term effect of N, Fe sulfate, and plant growth regulators (PGRs) on ABG populations in a creeping bentgrass (CBG, Agrostis stolonifera L.) golf green. The study was established on a mixed stand of ‘L‐93′ CBG (∼75%) and ABG (∼25%) and managed as a putting green in University Park, PA, from 2012 to 2018. Treatments included ammonium sulfate (24 and 147 kg ha−1 yr−1), Fe sulfate (0, 12, or 49 kg FeSO4 ha−1 application−1), and the PGRs trinexapac‐ethyl (TE, 0.043 kg a.i. ha−1 application−1), flurprimidol (FL, 0.28 kg a.i. ha−1 application−1) and a nontreated control. Treatments were initiated in late April or early May each year and reapplied where required every 3 wk for nine applications annually. In general, ABG populations were lowest under lower N rates and with applications of FL. The long‐term effect of FeSO4 was minimal. In the first year of this study (2012), turfgrass quality was reduced, but quality levels generally increased in subsequent years. Although low N and FL may reduce ABG and high N and TE may increase ABG, seasonal variations in environmental conditions may reduce the efficacy of these treatments.