Complementing Late-Season Nitrogen Fertilization of Cool-Season Turfgrass Putting Greens with Trinexapac-ethyl

Considering the vast number of golf course putting greens (PGs) comprised of creeping bentgrass (Agrostis stolonifera L.) and annual bluegrass (Poa annua L.) polystands; greater understanding of seasonal growth response to fall applications of growth regulators and/or N fertilizers is needed. The objective was to determine how timing of fall trinexapac-ethyl (TE; 4-[Cyclopropyl-a-hydroxymethylene]-3,5-dioxo-cyclohexanecarboxylic acid ethyl ester) plant growth regulator and/or N application rate influence(s) PG N assimilation, removal, and spring canopy density. Field studies were initiated on a mixed creeping bentgrass + annual bluegrass PG in September 2009 or 2010. Foliar applications of TE at 0, 0.044+0.044, or 0.088 kg ha(-1) were made in combination with soluble N at 30 or 60 kg ha(-1). Treatment initiations, recurring every 10 +/- 1 d and centered on 15 October (30-yr average date of first frost), represent the four treatment timings. Fall N rate directly influenced PG density but did not interact with TE. Compared to the 30 kg ha(-1) N rate, significantly lesser proportions of the 60 kg N rate were removed by mowing. Fall and early-spring PG growth decreased linearly with later N application dates, yet application timing significantly interacted with TE. Late fall TE treatment reduced early-spring shoot growth as much as 20%.