Seedling Annual Bluegrass Suppression with Autumn Applied Plant Growth Regulators.

Golf course managers are continually seeking new methods and products to suppress Poa annua L. (ABG) in golf turf. A field study was conducted in two consecutive years to evaluate the effect of the plant growth regulators (PGRs): flurprimidol (FL), paclobutrazol (PB), trinexepac-ethyl (TE) and a FL+TE tank-mix for their ability to suppress ABG seedling encroachment. Application rates for FL and PB were 0.28 or 0.56 kg a.i. ha^-1, while TE and FL+TE rates were 0.14+0.06 kg a.i. ha^-1 and respectively. Initially, all PGRs were applied three times on 28 d intervals starting on 31 August. In year two, two additional FL treatments were added and applied on 14 d intervals. All PGRs were compared to untreated turf and prodiamine, 0.38 kg a.i. ha^-1, controls. Prior to initiating treatments, glyphosate was applied on 21 Aug. to the study area which contained a mature, mixed stand of ABG and creeping bentgrass with a developed ABG seedbank. Throughout the study the experimental area was kept well irrigated to promote seedling development. By 12 Dec. of each year, ABG coverage ranged from 22-91 and 4-80% for year one and two, respectively. The most effective treatments for ABG suppression were prodiamine, both PB treatments and FL 0.56 kg a.i. h^-1 14 d treatment. The least effective treatments were TE alone, FL 0.28 kg a.i. ha^-1 28 d, and the TE+FL tank-mix.