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.