Annual Bluegrass (Poa annua L.) Seed Production and Viability Influenced by Plant Growth Stages and Various Chemical Treatments.

Annual bluegrass (Poa annua L.) is a prolific seed producer at any mowing height. Formation of seedheads can significantly reduce turf aesthetics and playability. Effective seedhead suppression requires proper timing of plant growth regulators (PGR’s), which is often difficult under field conditions. Therefore, a greenhouse study was conducted to determine the optimal plant growth stage to suppress annual bluegrass seedheads. Treatments included the PGR’s; Trinexapac-ethyl (0.06 kg ai ha^-1), Ethephon (3.8 kg ai ha^-1), Ethephon + Trinexapac-ethyl (3.8 + 0.06 kg ai^-1), Mefluidide (0.07 kg ai^-1), Flurprimidol (0.14 kg ai^-1), Paclobutrazol (0.224 kg ai ha^-1) and Maleic hydrazide (1.12 kg ai ha^-1) or herbicides; Methizolin (0.5 kg ai ha^-1) and Bispyribac-sodium (0.0124 kg ai ha^-1).  All treatments were applied to plants at three different growth stages in a randomized complete block design with 6 replications.  Growth stages included pre-boot, boot and flowering.  Weekly evaluations included plant height, density, color, quality, seedhead count, and canopy area (using digital image analysis).  Seed viability was also evaluated by subjecting seed to a tetrazolium test.  Plant height and canopy area were significantly reduced, compared to the untreated control, following applications of Paclobutrazol or Ethephon + Trinexapac-ethyl at the pre-boot or boot growth stage.  Complete results will be discussed with poster.