Trinexapac-ethyl Restricts Shoot Growth and Improves Quality of `Diamond' Zoysiagrass Under Shade

Abstract

Turfgrass is grown under extremely variable light intensities. This presents difficult management problems, and methods are needed to improve turf performance under variable shade conditions. Two experiments were conducted to determine the influence of trinexapac-ethyl (TE) on turf performance and physiological responses of `Diamond' zoysiagrass [Zoysia matrella (L.) Merr.] under several light intensities. In a polyethylene-roofed greenhouse, `Diamond' was sodded in 12 wooden boxes (1.2 × 1.2 × 0.16 m) (Expt. 1) and 18 fiber containers (55 × 38 × 12 cm) (Expt. 2). Treatments applied to boxes or containers included three levels of shade (40%, 75%, and 88%) with and without multiple TE applications at 48 g·ha-1 of active ingredient. Without TE treatment, vertical shoot growth increased linearly with increasing shade levels. Excessive shoot growth under 75% and 88% shade exacerbated energy depletion, as evidenced by the 45% and 67% lower rhizome mass and the 37% and 65% lower total nonstructural carbohydrate content (TNC), respectively, compared with turf under 40% shade. Trinexapac-ethyl reduced excessive vertical shoot growth and increased rhizome mass and TNC. Mean turf quality was increased by 0.7 and 1.4 units for turf receiving multiple TE applications under 75% and 88% shade, respectively. Trinexapac-ethyl did not increase turf quality or TNC under 40% shade. Canopy photosynthetic rate (Pn) was not affected 4 weeks after the initial TE treatment under any shade level. However, 34 weeks after the initial TE treatment a 50% higher Pn was observed for turf treated with TE under 88% shade, possibly because of higher tiller density. Repeated TE application increased turf quality and provided more favorable physiological responses (such as TNC and Pn) under 75% and 88% shade, where conditions favored vertical shoot growth. However, little or no improvement in turf quality was observed under 40% shade, where conditions favored slow vertical shoot growth. Chemical name used: 4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxo-cyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl).