Effects of growing degree day based trinexapac‐ethyl application on ultradwarf hybrid bermudagrass putting green quality and ball roll

Application of plant growth regulators to hybrid bermudagrass [ Cynodon dactylon  (L.) Pers. ×  Cynodon transvaalensis  Burtt Davy] putting greens is a common management practice used to reduce clipping yield and improve aesthetic and functional turfgrass quality. Growing degree day (GDD) models have explored the effects of plant growth regulator application timing on ultradwarf hybrid bermudagrass clipping yield. However, there is a need for research evaluating effects of GDD‐timed plant growth regulator applications on turfgrass quality and ball roll. A field study was conducted in summer 2018 at three locations (Knoxville, TN; Raleigh, NC; and Starkville, MS) to determine the effects of trinexapac‐ethyl (TE) applied according to a GDD model on ultradwarf hybrid bermudagrass putting green quality and ball roll compared to calendar‐based treatment (i.e., weekly or twice‐weekly). For GDD applications, TE was applied at either 20 or 33 g ha −1 . GDD based applications were made once 220 GDD (base 10°C) accumulated after each treatment. TE was applied at either 20 or 33 g ha −1 for weekly treatments and rate reduced to either 14 or 16 g ha −1 for the twice‐weekly treatment. In all locations, TE applied on a 220 GDD 10C schedule resulted in turfgrass quality greater than or equal to that of the weekly and twice‐weekly applied treatments. Ball roll distance was slightly lower in plots treated with TE every 220 GDD 10C compared to the weekly and twice‐weekly treatments, although differences may be negligible to golfers (13 to 23 cm). Ball roll distance was negatively correlated with clipping yield (−0.37 to −0.69). Turfgrass managers choosing to regulate ultradwarf hybrid bermudagrass greens with TE should consider applying on a GDD rather than calendar‐based interval to achieve improved turfgrass quality without sacrificing ball roll distance.