Plant growth regulator effects on winter hardiness of annual bluegrass putting green turf

Abstract

AbstractCold deacclimation sensitivity has been cited as an important factor associated with winterkill susceptibility of annual bluegrass (Poa annua L.). Increased potential for deacclimation for this species has been attributed to higher metabolic activities in response to warm winter temperatures. We hypothesized that using plant growth regulators to inhibit turfgrass growth and metabolism during winter months could potentially suppress premature deacclimation and increase survival of annual bluegrass. The specific objectives of this study were to examine the effects of varying rates of autumn‐applied trinexapac‐ethyl (TE) and prohexadione‐Ca (PC) on winter hardiness and spring recovery of an annual bluegrass putting green. The study was conducted over the winters of 2015–2016 and 2016–2017. Treatments included an untreated control and four rates of TE (0.05, 0.10, 0.2, and 0.4 kg a.i. ha–1) and PC (0.06, 0.12, 0.25, and 0.50 kg a.i. ha–1). Freezing tolerance was assessed based on controlled freeze tests to estimate the lethal temperature resulting in 50% regrowth (LT50). General turfgrass health was also assessed based on visual turf quality and normalized difference vegetation index (NDVI). Late‐autumn PGR applications impacted the freezing tolerance of annual bluegrass during Year 1, but no treatment effects were detected in Year 2. Plant growth regulator treated turf, pooled over chemicals and rates, exhibited lower freezing tolerance (Year 1), turf quality, and NDVI (Years 1 and 2) compared to untreated turf particularly at the higher application rates. By the end of May in both years, all treatments recovered to the same levels.