Plant Growth Regulators Efficiency for the Removal of Annual Bluegrass from a Creeping Bentgrass Putting Green.

Annual bluegrass (Poa annua; ABG) is an undesirable and invasive plant in creeping bentgrass (Agrostis stolonifera; CBG) putting greens. Thus, ABG suppression is an important management practice for some turf areas. Common plant growth regulators (PGRs) used in turfgrass inhibit gibberellic acid (GA) production and accumulation. This differentially alters shoot growth on putting green species which, in previous studies, has been shown to suppress ABG growth more than CBG. A field study was conducted in 2016 and 2017 at the Hancock Turfgrass Research Center in East Lansing, MI to evaluate the efficacy of trinexapac-ethyl (TE), flurprimidol (F), paclobutrazol (P), combinations of those three chemicals, and methiozolin (M) on the suppression of ABG in a CBG putting green. Visual turfgrass quality, percent ABG cover, multispectral radiometry for normalized difference vegetation index, and digital image analysis for dark green color index were measured. Treatments of M decreased ABG by 93.7% while TE+F+P combination and P alone decreased ABG by 55.2% and 52.3% when compared to the untreated control respectively. The TE+F+P combination and TE+F combination had better turfgrass quality when compared to the untreated control while M was no different than the untreated control. Combination of GA inhibiting PGR’s and M were found to be effective at decreasing the amount of ABG within a CBG putting green. These results suggest that a more uniform CBG putting green may be obtained by applying combinations of GA altering PGRs by suppressing ABG.