Influences of Plant Growth Regulators on Seedhead Development of Annual Bluegrass (Poa annua L.).

Annual bluegrass (Poa annua L.) is one of the most problematic weeds on golf courses, especially on creeping bentgrass (Agrostis stolonifera L.) putting greens. As a prolific seed producer, annual bluegrass plants can produce viable seeds underneath the mowing lines, increasing the difficulty to eradicate them. Currently, superintendents still rely heavily on plant growth regulators (PGRs) to manage this species. The objective of this project was to evaluate commonly used PGRs for seedhead production of annual bluegrass when applications were made at various developmental stages. Annual bluegrass seeds collected from local turf area were germinated in the greenhouse condition and single plants were propagated into individual pots. Treatment included seven PGRs at label suggested rates in addition to an untreated control, and the PGRs were applied at pre-boot, boot, or flower stages. Treatments were arranged as a factorial combination in a randomized complete block design with 4 replications. At 8 weeks after treatment (WAT), seedheads were harvested and their total counts per plant were determined. For each plant, ten randomly selected seedheads were also bagged individually and the number of seeds for each seedhead were determined.  Current results showed significant PGRs and application timing effects on the number of seedheads produced. Despite the application timing, plants treated by ethephon or paclobutrazol yielded the least amount of seedhead with up to 40 or 50% reduction compared to the untreated control. Application timing also significantly influenced the seedhead productions. PGRs applied at boot stage showed in average 47% less seedheads per plant, compared to applications made at flower stage where in average 171 seedheads were produced. This is an ongoing project and more details will be discussed in the presentation.