The Effect of Trinexapac Ethyl and Three Nitrogen Sources on Creeping Bentgrass Agrostis stolonifera L. Grown Under Three Light Environments.

Shade stress on creeping bentgrass (Agrostis stolonifera L.) causes leaf elongation and reduced energy availability for growth. Decreased quantity or photosynthetic photon flux density (PPF) and quality or the red: far red light ratio (R:FR) of light affects the turfgrass morphology. Plants increase production of giberellic acid and reduce available non-structural carbohydrates. The object of the study was to determine which source of nitrogen (N) is best suited to retaining turfgrass quality in shade and investigate if the plant growth regulator trinexapac-ethyl [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (TE) (Syngenta AG, Switzerland) can delay loss of quality of bentgrass under tree shade. Field studies were conducted on ‘Penncross’ creeping bentgrass in Columbus OH, in 2006 and 2007. Three light environments were developed; full sun (FS), reduced R:FR (DS), and reduced PPF (NS). Light reduction was >90% in shaded areas and the R:FR ratio was 0.38 in the DS area, 1.28 in NS, and 1.29 in FS. The nitrogen treatments included (NH₂)₂CO, Ca(NO₃)₂ and (NH₄)₂SO₄ foliarly applied weekly at a rate of 0.43g m^-2, TE was applied bi-weekly at 0.3975 L ha^-1. Chlorophyll content, along with soluble carbohydrates, flavonoids, turf canopy color, dry matter and canopy densities were measured. There were no differences in soluble carbohydrate levels among treatments. Chlorophyll levels varied between TE treated and non-treated areas. Trinexepac-ethyl had no impact on flavonoids. Nitrogen treatments caused differences in dry matter and carbohydrate content. Applying (NH₂)₂CO in combination with TE provided the best visual quality surface as the season progressed. Trinexepac-ethyl was effective in reduced PPF conditions and R:FR conditions. Trinexepac-ethyl efficiency in both light environments suggests that prior shade research using NS on creeping bentgrass is relevant to shade management in private industry. Applications of (NH₂)₂CO increased total chlorophyll content, otherwise few differences were observed due to nitrogen.