Plant growth regulators differentially suppress goosegrass and smooth crabgrass in creeping bentgrass turf

Goosegrass and smooth crabgrass control in creeping bentgrass is difficult due to a lack of selective herbicides. Based on preliminary field observations, we hypothesized that paclobutrazol and flurprimidol would reduce the overall competitiveness of goosegrass and smooth crabgrass in creeping bentgrass. Greenhouse and field studies were designed to evaluate the effect of several plant growth regulators (PGRs) on goosegrass and smooth crabgrass competitive indices. In greenhouse studies, flurprimidol, paclobutrazol, trinexapac-ethyl, and prohexadione-calcium were applied either preemergence only or preemergence plus two biweekly postemergence applications to goosegrass and smooth crabgrass plants to simulate the first 1.5 months of typical PGR programs utilized on golf courses. Two wk after the final postemergence treatment, above-ground biomass, and root biomass were recorded. Programmatic flurprimidol and paclobutrazol applications reduced smooth crabgrass above-ground biomass 67 and 69%, respectively, and more than trinexapac ethyl or prohexadione-calcium. When averaged across application programs, flurprimidol and paclobutrazol reduced smooth crabgrass root biomass 74% and goosegrass biomass 73-80%. Field studies were established to further evaluate the influence of PGR on smooth crabgrass coverage in creeping bentgrass turf. Treatments consisting of flurprimidol, trinexapac-ethyl, flurprimidol plus trinexapac-ethyl, paclobutrazol, and fenoxaprop-p were applied every three wk from April to August. Weed coverage data were collected throughout the growing season, and final smooth crabgrass control data were collected at the end of the season. In general, flurprimidol-containing treatments more effectively reduced smooth crabgrass coverage throughout the growing season than trinexapac ethyl. After the studies, flurprimidol containing programs controlled smooth crabgrass 68-73%, greater than any other PGR program evaluated. Results from these studies indicate flurprimidol may be used to control smooth crabgrass or goosegrass in creeping bentgrass turf effectively. These are the first reported data regarding the use of flurprimidol for smooth crabgrass or goosegrass control in turf.