Development of a Growing Degree Day Model for Plant Growth Regulators on Ultradwarf Bermudagrass.

Plant growth regulators (PGRs) are widely applied to ultradwarf bermudagrass putting greens. The duration of regulation on ultradwarf bermudagrass putting greens from PGRs is not well documented. The purpose of this research was to develop a growing degree day (gdd) model for prohexadione calcium and trinexapac-ethyl on ‘Champion’ ultradwarf bermudagrass. Growth was evaluated in response to PGR applications by collecting clippings. Clippings were collected 2-3 times per week, oven dried for at least 24 hours, separated from any debris or sand, and weighed. Turfgrass quality and ball roll distance measurements were taken weekly. The growing degree day model using base 10°C showed that prohexadione calcium at a rate of 0.056 g/m² reached average maximum suppression at 128.45 gdd, prohexadione calcium at a rate of 0.112 g/m² reached average maximum suppression at 114.74 gdd, and trinexapac-ethyl at a rate of 118.294 ml/m² reached average maximum suppression at 161.75 gdd. Average maximum growth suppression for the low rate of prohexadione calcium was 80.5%, for the high rate of prohexadione calcium was 84%, and for trinexapac-ethyl was 82% of non-treated controls. Turfgrass quality and ball roll distances varied among treatments and will be presented in detail in the poster.