Plant growth regulators are an effective tool that can use to reduce vertical shoot growth, increase shoot density, and improve putting green playability. Traditionally, PGRs have been applied on a calendarbased
schedule, but growing degree-day models for reapplication intervals have been developed recently for trinexapac-ethyl, paclobutrazol, and prohexadione-Ca on creeping bentgrass and ultradwarf bermudagrass putting greens. There is, however, a lack of data available to develop similar models for annual bluegrass putting greens. Moreover, it is unclear what effect nitrogen rate will have on GDD models for PGR reapplication interval. Therefore, the objectives of this project are to develop a growing degree day model for PGR (trinexapac-ethyl and prohexadione-Ca) reapplication interval on annual bluegrass putting greens and determine if nitrogen rate has an influence on a growing degree day model for annual bluegrass putting greens.