Herbicide and Plant Growth Regulator Programs for Controlling Annual Bluegrass (Poa annua L.) in Recently Established Creeping Bentgrass (Agrostis palustris Huds.) Fairway Turf.

Annual bluegrass (Poa annua L.) [ABG] is a cosmopolitan weed that can be found anywhere in the world where human activity is present. ABG quickly invades creeping bentgrass (Agrostis palustris Huds.)[CBG] fairways in cool-temperate climates. Chemical methods to limit ABG invasion include preemergence and postemergence herbicides and plant growth regulators [PGRs]. Two 3-factor trials were initiated in 2007 in East Lansing, Michigan to examine the effects of treatment combinations to limit ABG invasion in CBG fairways with less than 5 percent initial invasion. Factors included preemergence herbicide, at three levels: none, dithiopyr, or cumyluron; PGR, at three levels: none, flurprimidol, or paclobutrazol; and postemergence herbicide, at two levels: none or bispyribac-sodium. ABG populations were determined in the spring and fall of each year. Treatment combinations including PGR and bispyribac-sodium and paclobutrazol + cumyluron reduced ABG cover by 93, 96, and 96% in the spring of 2008, 2009, and 2010, respectively. Turfgrass injury was evaluated throughout the trial period on a 1-9 scale where, 1=no injury and 9= complete blighting. Turfgrass injury associated with the same treatment combinations averaged 5.0, 3.0, and 4.0 during the fall assessments in 2007, 2008, and 2009, respectively.