1. Evaluation of Combinations of Bispyribac-Sodium or Amicarbazone with Trinexapac-Ethyl or Paclobutrazol for Annual Bluegrass Control On Creeping Bentgrass Greens Justin Quetone Moss 1, Kemin Su 1, and Bishow Poudel 1 1 Oklahoma State University (OSU), Department of Horticulture and Landscape Architecture Evaluation of Combinations of Bispyribac-Sodium or Amicarbazone with Trinexapac-Ethyl or Paclobutrazol for Annual Bluegrass Control On Creeping Bentgrass Greens Justin Quetone Moss 1, Kemin Su 1, and Bishow Poudel 1 1 Oklahoma State University (OSU), Department of Horticulture and Landscape Architecture Introduction Acceptable annual bluegrass (Poa annua L.) seedhead reduction in golf greens can occur with repeated application of plant growth regulators, but complete control of annual bluegrass is difficult to achieve. Bispyribac-sodium is labeled to control annual bluegrass in creeping bentgrass (Agrostis stolonifera L.) fairways but is not labeled for use on golf course greens. Amicarbazone is a triazolinone herbicide which is currently being evaluated for use in turfgrass management. Objectives The objective of this research was to determine the annual bluegrass control and phytotoxicity to creeping bentgrass from application of low rates of bispyribac-sodium or amicarbazone with and without trinexapac-ethyl or paclobutrazol. Materials & Methods Cont. Results Annual bluegrass control at 28 d after initial treatment was 0% for all plots regardless of treatment (data not shown). Phytotoxicity was significantly greater in bispyribac-sodium treated plots (Table 1), but no treatments caused unacceptable phytotoxicity (Figures 2-8) or turf quality (Table 2.) (57 g ai/ha once), or paclobutrazol (224 g ai/ha once) with an untreated control. All plots were fertilized weekly with soluble fertilizer (5 kg N/ha and 1 kg FeSO4/ha). Experimental design was a randomized complete block with four replications. Treatments and fertilizer were applied with a CO 2 bicycle type research sprayer (Figure 1.) Plots were visually rated weekly for annual bluegrass control, turf quality, and herbicide phytotoxicity. The data was analyzed using the SAS GLM procedure for ANOVA and Fisher’s Protected LSD at the p=0.05 level. Figure 2: Untreated control Figure 5: Bispyribac-sodium (14.8 g ai/ha ) + paclobutrazol (224 g ai/ha) Figure 7: Amicarbazone (100 g ai/ha) + trinexapac-ethyl (54 g ai/ha) Figure 8: Amicarbazone (100 g ai/ha) + paclobutrazol (224 g ai/ha ) Acknowledgements Research support was provided by the Oklahoma Agricultural Experiment Station. Figure 1: OSU Graduate Student, Bishow Poudel with CO 2 bicycle-type research sprayer. Table 1. Creeping Bentgrass Phytotoxicity Ratings Four Weeks After Initial Treatment (WAIT) 1. Table 2. Creeping Bentgrass Turfgrass Quality Ratings Four Weeks After Initial Treatment (WAIT) 1. Figure 4: Bispyribac-sodium (14.8 g ai/ha) + trinexapac-ethyl (54 g ai/ha ) Figure 3: Bispyribac-sodium alone (14.8 g ai/ha) Figure 6 : Amicarbazone alone (100 g ai/ha ) Conclusions Low rates of bispyribac-sodium with or without trinexapac-ethyl or paclobutrazol applied to creeping bentgrass greens in the spring did not significantly control annual bluegrass, but did not cause unacceptable turf quality or phytotoxicity. Further work is needed to assess long term use of low rates of bispyribac- sodium and amicarbazone on annual bluegrass control in creeping bentgrass greens. This work will be repeated in 2010 with additional treatments. Materials & Methods Field research plots (1.5 x 1.5 m) were treated during spring 2009 over a 28 d period at Stillwater, OK. Treatments were: bispyribac-sodium (9.9 to 14.8 g ai/ha every 7 d) alone, amicarbazone (50 and 100 g ai/ha every 28 d) alone, and with either trinexapac-ethyl 1 Means followed by the same letter are not significantly different at p=0.05.