Reducing Poa Annua through the Use of Plant Growth Regulators On Putting Greens.

Field studies were conducted on practice putting greens at Downriver and Esmeralda Golf Courses in Spokane, WA and Avondale Golf Club in Hayden Lake, ID.  Objectives were to evaluate the effectiveness of various plant growth regulators (PGRs) and application rates to reduce the level of Poa annua in a mixed stand of creeping bentgrass and Poa annua.

At Downriver and Esmeralda, PGR treatments included flurprimidol (0.14 and 0.28kg a.i. ha^-1), flurprimidol + trinexapac-ethyl (0.06 and 0.12lbs a.i. A^-1), paclobutrazol (0.14kg a.i. ha^-1), and trinexapac-ethyl (0.1 kg a.i. ha^-1).  At Avondale, PGR treatments included flurprimidol (0.22kg a.i. ha^-1), flurprimidol + trinexapac-ethyl (0.06 and 0.12lbs a.i. A^-1), paclobutrazol (0.14kg a.i. ha^-1), and trinexapac-ethyl (0.1 kg a.i. ha^-1).  Products were applied every two weeks starting in mid-May and ending in mid-September.  Prior to initiating PGR applications, the practice putting greens at all sites had approximately 60%/40% creeping bentgrass (blend of ‘T-1’ and ‘Alpha’)/Poa annua.  For all locations, percent creeping bentgrass, Poa annua color, creeping bentgrass color, and recovery from aerification was evaluated.

At Downriver, flurprimidol + trinexapac-ethyl (0.12lbs a.i. A^-1), paclobutrazol (0.14kg a.i. ha^-1), and flurprimidol (0.28kg a.i. ha^-1) resulted in greatest bentgrass coverage with approximately 81% in mid-August.  While these PGRs resulted in greatest creeping bentgrass coverage, flurprimidol (0.28kg a.i. ha^-1) and paclobutrazol (0.14kg a.i. ha^-1) also resulted in greatest discoloration of both species when applied early and late in the growing season.  At Avondale, results slightly varied.  By the beginning of September, paclobutrazol (0.14kg a.i. ha^-1) and flurprimidol (0.22kg a.i. ha^-1) showed highest percent creeping bentgrass with approximately 80% coverage.  However, flurprimidol + trinexapac-ethyl applied at 0.12lbs a.i. A^-1 yielded 67% creeping bentgrass.

Results suggest that implementing a PGR program is effective for increasing the amount of creeping bentgrass, while reducing Poa annua population on putting greens.