Effects of Nitrogen and the Combination of Trinexapac-Ethyl, Paclobutrazol, and Flurprimidol on Creeping Bentgrass Putting Greens

Abstract

Golf course putting greens are evaluated based on aesthetic qualities and playability. Cultural practices such as nitrogen (N) fertility and the use of plant growth regulators (PGRs) can influence both quality and the visual aesthetic of a putting green surface. The objectives of this research were to assess the effects of 1) N rate and the combination of trinexapac-ethyl, paclobutrazol, and flurprimidol on the playability and turfgrass quality of creeping bentgrass (Agrostis stolonifera cv ‘777’), and 2) N rate and the combination of trinexapac-ethyl, paclobutrazol, and flurprimidol on the severity of the disease commonly referred to as dollar spot, caused by the fungus (Clarireedia jacksonii) on a research putting green in north-central Oklahoma. Nitrogen application treatments included five rates (0, 4.9, 9.8, 14.7, 19.5 kg ha^-1 N per application) arranged in factorial with three rates of (0.9, 1.3, 1.6 L ha^-1 per application) a mixture of trinexapac-ethyl (1.4%), paclobutrazol (5.6%), and flurprimidol (5.6%). Applications were made every 14 days for 20 weeks starting 1st May 2021 and 2022. Golf ball roll distance (BRD) was measured using a Stimpmeter at 7 and 14 days after each N and PGR application. Visual turfgrass quality (TQ) ratings, normalized difference vegetation index (NDVI), normalized difference red edge (NDRE), and dark green color index (DGCI) were measured weekly to quantify aesthetic quality. Visual dollar spot disease incidence and digital image analysis (DIA) were used to assess dollar spot disease severity. For TQ, NDVI, and NDRE the N treated plots had higher ratings than the non-fertilized plots. Plots receiving PGR had significantly lower NDVI than the non-regulated plots. In 2021, the 0 and 4.9 kg ha^-1 N plots resulted in greater BRD than the other three N rates, while a similar pattern was found in 2022. The use of PGR did not influence BRD in 2021, but the highest rate increased BRD in 2022. In 2021, the high N rate (19.5 kg ha^-1 N) reduced disease incidence, while in 2022 plots receiving N had reduced disease compared the 0 N rate. Visual disease was also decreased by PGR applications. For each year, average dollar spot size and diameter were decreased by using the high N rate (19.5 kg ha^-1 N). Plots treated with PGR had less dollar spot disease than the non-regulated plots. Increasing N resulted in lower BRD but improved turfgrass quality. Both increasing N rates and the use of PGR decreased dollar spot severity and increased turfgrass quality.