Growth response of three turfgrass species to nitrogen and trinexapac-ethyl in shade
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abstract
Previous research on the potential of the gibberellin inhibiting growth regulator trinexapac-ethyl (TE) [4-(cyclopropyl--hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester] to improve quality and density of shaded turfgrass has been conducted under neutral-density shade. However, some phytochrome-mediated growth responses of turfgrass, such as tillering, are different under deciduous shade versus neutral-density shade. The objectives of this study were to investigate 1) whether TE would result in improved stand density and quality of turfgrass grown under deciduous shade as has been observed under neutral-density shade and 2) the shade tolerance of sheep fescue (Festuca ovina L. `Quatro') compared to tall fescue (Festuca arundinacea Schreb. `Plantation'), and rough bluegrass (Poa trivialis L.). Trinexapac-ethyl at either 0 or 29 kgha1 a.i. and nitrogen at 12 or 36 kgha1 were applied on 23 May, 3 July, and 15 Aug. 2003 and 21 May 2004 to each species in a randomized complete block design under deciduous shade (about 9% of full sun). Clipping yield, color, and density data were collected for 6 weeks after the May applications in each year. Visual quality was assessed for 6 weeks after application in 2004 only. In 2003, TE significantly reduced clipping yields by 35% to 50% on sheep fescue, 58% to 76% on tall fescue and 55% to 80% on rough bluegrass. However, in 2004, yield reduction was 0% to 50% for all three species and there was no interaction between week, TE, and species. `Plantation' tall fescue had the highest overall visual quality and density. Sheep fescue also provided an acceptable quality turf stand. TE application did not significantly impact the quality of these species. Rough bluegrass performance was unacceptable, and high rate applications of TE to this species in shade resulted in significant (P < 0.05) losses in density. Trinexapac-ethyl application, based on the results of this study, may not enhance turf quality of cool season grasses grown under dense tree shade.
