Management of Annual Bluegrass (Poa annua L.) Seedheads on Creeping Bentgrass (Agrostis stolonifera L.) Putting Greens with Plant Growth Regulators.

Annual bluegrass (Poa annua L.) is a problematic weed in turfgrass.  It is a prolific seed producer at any mowing height, and the formation of seedheads seriously reduces turf aesthetics and playability. Plant growth regulators have been used to suppress Poa seedhead production on creeping bentgrass (Agrostis stolonifera L.) putting greens. Effective seedhead suppression requires proper timing of treatments, typically prior to seedhead formation. Under field conditions, estimates of seedhead formation are difficult due to the wide range of environmental conditions that seedhead formation occurs. Consequently, sequential applications are often necessary. In this experiment, field plots were established on putting greens of two local golf courses in Columbia, Missouri to investigate seedhead suppression by using different PGRs as single or sequential applications spaced 2 weeks apart. Plots were arranged as a split-plot design with four replications.  Whole plot treatments included different PGRs including: mefluidide (0.07 kg ai ha^-1), ethephon (3.8 kg ai ha^-1) alone, or with trinexapac-ethyl (0.06 kg ai ha^-1), and an untreated control. The sub-plots were either single or sequential applications. Seedhead counts, turf qualities and phytotoxicity were monitored on a weekly basis. Regardless of application times, all treatments significantly reduced seedhead counts compared to the untreated control in spring 2011. Among the treatments, ethephon alone or with trinexapac-ethyl resulted in lower seedhead production compared to mefluidide treated plots. The highest seedhead reduction was found in the plots treated with ethephon and trinexapac-ethyl in early May, where ~95% of seedhead reduction was recorded. Two sequential applications did improve seedhead suppression, especially during the period of peak seedhead production at Columbia MO (May). A separate greenhouse experiment was established with similar treatments in the field research.  Applications were made at pre-boot, boot, and flowing stages of Poa. After plants mature, seeds will be collected from individual plants and enumerated.  Seed viability will be assessed using a tetrazolium test on random lots of 100 seeds.  Results from the field and greenhouse experiments will be discussed in more detail.