Plant growth regulators alter the growth of 'Tifway' bermudagrass (Cynodon transvaalensis x C. dactylon) and selected turfgrass weeds

Growth-regulating characteristics of trinexapac-ethyl, paclobutrazol, and flurprimidol were investigated on 'Tifway' bermudagrass and four turfgrass weeds (large crabgrass, goosegrass, bahiagrass, and purple nutsedge). All treatments reduced the height of Tifway bermudagrass (25 to 37%) and large crabgrass (14 to 34%), but the height of purple nutsedge, goosegrass, and bahiagrass was not consistently changed. In 1995, all rates of trinexapac-ethyl reduced clipping weights of Tifway bermudagrass (70 to 87%) and bahiagrass (53 to 59%) more than large crabgrass, goosegrass, or purple nutsedge (< 39%). Trinexapac-ethyl (0.4 kg ai/ha) and paclobutrazol (1.1 kg ai/ha) applications increased both large crabgrass clipping weight and canopy visible density. Increased large crabgrass density was attributed to greater tiller numbers with trinexapac-ethyl (60 tillers/pot) and paclobutrazol (63 tillers/pot) compared to untreated large crabgrass plants (53 tillers/pot). Weed growth was not suppressed as much as Tifway bermudagrass growth; therefore, turfgrass stands may be adversely affected by plant growth regulator use under weedy conditions.