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Previous research on the potential of the gibberellin inhibiting growth regulator trinexapac-ethyl (TE) [4-(cyclopropyl-α-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 kg·ha–1 a.i. and nitrogen at 12 or 36 kg·ha–1 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.
A 3-year study was conducted to evaluate the comparative performance of zoysiagrass (Zoysia spp.) cultivars for shaded environments in which inputs are minimized. Included in the study were commercial cultivars Diamond, Cavalier, Royal, Shadow Turf, Zorro, Zeon, Jamur, Crowne, Palisades, and Meyer. In July 2006, grass plugs were planted in a shade nursery comprised of live oak trees providing 89% shade. From 2007 to 2009, turf plots were periodically evaluated for quality, density, color, vertical canopy height, and extent of lateral spread. Overall turfgrass quality was noticeably reduced by the heavily shaded environment; however, some cultivars attained acceptable levels during midsummer periods. A turf performance index (TPI) was generated for ranking the cultivars that represented the number of times an entry occurred in the top statistical group across all parameters and rating dates. ‘Royal’, ‘Zorro’, and ‘Shadow Turf’ were the cultivars ranking in the top statistical grouping most often throughout the study. The results suggest that Z. matrellas may be better adapted than Z. japonicas for heavily shaded environments where inputs are conserved.