Plant Growth Regulator Selection and Application Rate Influence Annual Bluegrass Control in Creeping Bentgrass Putting Greens

Field experiments were conducted in 2009 and 2010 on two golf course practice putting greens in Spokane, WA (Esmeralda), and Hayden Lake, ID (Avondale), consisting of an approximate 50% blend of creeping bentgrass (Agrostis stolonifera L.) (CBG) and annual bluegrass (Poa annua L.) (ABG). Various regimes of trinexapac-ethyl (TE), flurprimidol (FL), paclobutrazol (PB), and TE + FL were investigated to determine which plant growth regulator (PGR) regime provided the greatest transition from ABG to CBG. Following PGR applications every two weeks over two growing seasons in the Northwest, PB at 0.28 kg/ha and FL at 0.22 and 0.28 kg/ha produced the greatest increase in CBG coverage, followed by TE + FL at 0.04 + 0.10 kg/ha. TE at 0.10 kg/ha consistently resulted in the least amount of CBG compared to other PGR treatments. While PGRs are an effective tool for superintendents to use for ABG suppression on putting greens, PGR selection, application rate, and application timing are important considerations for successful results.