Kentucky bluegrass growth responses to trinexapac-ethyl, traffic, and nitrogen

Understanding the whole-plant response of Kentucky bluegrass (Poa pratensis L.) to the plant growth regulator (PGR) trinexapacethyl (TE) [4-(cyclopropyl-alpha-hydroxy-methylene)-3,5-dioxo-cyclohexane-carboxylic acid ethyl ester] while subjected to traffic and variable N rates would facilitate recommendations regarding its safe and effective use. The objectives of this study were (i) to investigate the extent and duration of TE-induced shoot growth suppression on Kentucky bluegrass and determine any interactive traffic or N effects, and (ii) to investigate if TE-induced reductions in shoot growth affect tillering, rooting, and quality of Kentucky bluegrass, and determine any interactive traffic or N effects. Trinexapac-ethyl (0.27 kg ha(-1)) was applied to main plots three times a year at 6-wk intervals. Traffic was applied to subplots with a cleated roller. Four increasing rates of a slow-release N source were applied annually to sub-subplots. Trinexapac-ethyl consistently reduced clippings by 1 to 2 wk after treatment (WAT), with maximum suppression occurring at 3 to 4 WAT. Greater suppression occurred for July and August application dates relative to May. Traffic consistently reduced clippings and tiller density. Tiller density was increased by TE in 1996. Higher annual N did not, in general, affect tiller density, root mass, or quality. Repeated TE application did not affect Kentucky bluegrass root mass. Trinexapac-ethyl did not affect quality, while traffic consistently reduced it. Quality was poorest at the three highest N-rates under TE and traffic during the last treatment cycle of 1997. These results suggest caution when using TE on highly trafficked Kentucky bluegrass.