Annual bluegrass is a troublesome weed in golf course putting greens. The objective of this research was to evaluate creeping bentgrass putting green tolerance to bispyribac-sodium tank-mixed with paclobutrazol in the transition zone. Field trials with four replications were conducted in Oklahoma during 2009 and 2010 and in Missouri during 2010. The results of this study suggest that tank-mixing bispyribac-sodium with paclobutrazol may discolor creeping bentgrass putting greens but will not reduce turf quality below acceptable levels. Normalized vegetative difference index readings indicated no treatment differences in turf greenness at 4 and 8 wk after initial treatment. Weekly application of bispyribac-sodium at 12.4 g ha⁻¹ or biweekly application at 24.8 g ha⁻¹ alone or with monthly applications of paclobutrazol at 224 g ha⁻¹ did not cause unacceptable injury to creeping bentgrass putting greens during the spring.

Nomenclature: Bispyribac-sodium {2,6-bis[(4,6-dimethoxypyrimidin-2-yl)oxy] benzoic acid}; paclobutrazol; trinexapac-ethyl; annual bluegrass, Poa annua L. POAAN; creeping bentgrass, Agrostis stolonifera L. AGSST, ‘Penncross’.