Growing degree day models for plant growth regulator applications on ultradwarf hybrid bermudagrass putting greens

Abstract

Plant growth regulators (PGRs) are commonly applied to ultradwarf hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] putting greens during the growing season. Trinexapac-ethyl (TE) and prohexadione-Ca (PH) are PGRs that inhibit gibberellic acid biosynthesis and are used to reduce clipping yield and improve turfgrass visual quality. Growing degree day (GDD) models have optimized the timing of PGR reapplica-tions to creeping bentgrass (Agrostis stolonifera L.) putting greens, but no information is available regarding proper PGR reapplication timing on bermudagrass putting greens. The objective of this research was to develop a GDD model to determine optimal TE and PH application frequencies on bermudagrass putting greens. Field research was conducted on three ultradwarf cultivars at separate locations in the southeastern United States: ‘MiniVerde’ in Knoxville, TN, ‘Champion’ in Durham, NC, and ‘TifEagle’ in Starkville, MS. Peak yield suppression was 49 to 65% after TE application at 0.034 kg a.i. ha−1 and 50 to 54% after 0.154 kg PH ha−1. Peak suppression occurred later for TE (166-177 GDD calculated using 10°C as the base temperature [GDD10C]) than for PH (92-97 GDD10C), which resulted in an estimated PGR reapplication interval of 216 to 230 for TE and 120 to 126 GDD10C for PH. Enhanced clipping yield and rebound did not follow clipping yield suppression. The use of a GDD model to schedule PGR applications on bermudagrass putting greens has the potential to maximize PGR benefits; however, season-long implementation of this GDD model needs comparison with current PGR programs used on ultradwarf putting surfaces.