An experimental turfgrass growth regulator, V-10029, was compared with trinexapac-ethyl, a growth regulator used commonly on highly maintained turfgrasses, to evaluate growth suppression patterns and suppression of seedhead formation; the latter was evaluated on turfgrass species and annual bluegrass, a weedy species that appeared and developed seedheads in tall fescue. Plugs of creeping red fescue, Kentucky bluegrass, perennial ryegrass, and creeping bentgrass were taken from the field into a greenhouse. V-10029 at three rates (0.015, 0.029, and 0.059 kg/ha) was compared to an untreated control and trinexapac-ethyl at a label rate (0.382 kg/ha for perennial ryegrass and 0.287 kg/ha for the other four species). Of the eight replications for each treatment, four were not mowed for the purpose of evaluating suppression of seedhead formation, and four were used for weekly clipping collection to evaluate growth suppression. Compared to the untreated control, V-10029 at all three applied rates caused significant seedhead suppression in both tall fescue infested with annual bluegrass (> 90%) and perennial ryegrass (50 to 80%). Trinexapac-ethyl was not as effective, causing seedhead suppression levels of 57% in annual bluegrass found in tall fescue and 43% in perennial ryegrass. V-10029 caused unacceptable levels of discoloration (> 20%) in all turfgrass species, and discoloration increased with increasing rates of application. Patterns of growth suppression for tall fescue, Kentucky bluegrass, and perennial ryegrass, in response to V-10029 at all rates and to trinexapac-ethyl, were similar on a percent of suppression basis. Growth of creeping bentgrass was suppressed by V-10029 only at high rates. In contrast, creeping red fescue was significantly injured by V-10029 at all rates. The greatest growth suppression, in response for all treatments, occurred 2 to 3 wk after application. The effect of trinexapac-ethyl dissipated after 4 wk, while V-10029 was effective until 5 to 7 wk after treatment. Observed effects of V-10029 were consistent with its activity as an ALS-inhibiting herbicide and, therefore, as a Class D turfgrass growth regulator.

Studies were conducted for 12 wk from June 16 to September 8, 2003 and July 10 to October 4, 2004 with the objective of evaluating growth regulation, lateral regrowth, and injury of Tifway bermudagrass [Cynodon dactylon (L.) × C. transvaalensis Burtt-Davy Tifway] in response to two GA-inhibiting plant growth regulators, trinexapac-ethyl and flurprimidol. Trinexapac-ethyl was applied alone at 0, 0.052, and 0.104 kg ai/ha and flurprimidol alone at 0, 0.14, and 0.28 kg ai/ ha, plus all combinations. Applications were made every 3 wk for the duration of the study. Tifway bermudagrass clipping yield was reduced 33% and 54% by trinexapac-ethyl at 0.104 kg/ha at 4 and 8 wk after initial treatment (WAIT), respectively. Flurprimidol at 0.28 kg/ha reduced clipping yield 49% 8 WAIT. Lateral regrowth was reduced 20% 2 WAIT by trinexapac-ethyl at 0.104 kg/ha, and 26% 2 WAIT by flurprimidol at 0.28 kg/ha. Lateral regrowth was reduced 13% 4 WAIT by trinexapac-ethyl at 0.104 kg/ha, and 15% 4 WAIT by flurprimidol at 0.28 kg/ha. Overall, acceptable injury (<30%) was observed with a trinexapac-ethyl and flurprimidol tank mixture; however, this evaluation did not indicate an advantage in growth regulation when using a tank mixture of these products, compared to using them alone.