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) trinexapac‐ethyl (TE) [4‐(cyclopropyl‐α‐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.