Trinexapac-ethyl and nitrogen effects on creeping bentgrass grown under reduced light conditions

Shade is a major cause of poor performance and loss of turf, especially on putting greens. The objectives of this study were to determine the effects of trinexapac-ethyl (TE) [4-(cyclopropyl-alpha-hydroxymethylene)-3, 5-dioxo-cyclohexanecarboxylic acid ethylester] and nitrogen (N) on the performance and carbohydrate content of creeping bentgrass (Agrostis stolonifera L. cv. 'Penncross') grown under reduced light conditions (RLC). The effect of rate and frequency of TE applications to creeping bentgrass under RLC also were evaluated. Two field experiments were conducted during 1998 and 1999 in East Lansing, MI on an established sand-based putting green mowed to a height of 4 mm. In the first experiment (1998 and 1999), turf grown under 80% black shade cloth received multiple applications of TE (0, 0.042 or 0.070 kg a.i. ha(-1)) in combination with N (low = 150-185 kg N ha(-1) season(-1) or high = 212-235 kg N ha(-1) season(-1)). Turf quality and cover were reduced greatly under 80% shade. Application of TE increased turf cover from 6 to 33%, tillers from 40 to 52%, but had no effect on root mass when compared with turf not treated with TE. Fructose content increased by 40 and 37% in turf treated with TE at 0.042 and 0.070 kg a.i. ha(-1), respectively. No differences in tissue levels of other carbohydrates or starch were found. Turf cover was 3.3 to 7.2% greater in plots treated with low N when compared with high N. There were no significant interactions between TE and N. In the second experiment (1999), turf grown under 60% green shade cloth received TE (0, 0.025, or 0.050 kg a.i. ha(-1)) applied on 2- or 4-wk intervals. There were no differences in turf cover in bentgrass grown under 60% shade, regardless of TE treatment. In general, creeping bentgrass quality and color were improved by TE, when compared with untreated turf. Overall, data indicated that TE and judicious use of N can improve creeping bentgrass quality under RLC.