TEMPORAL SHIFTS IN PLANT COMPOSITION OF TURFGRASS MIXTURES ARE NOT AFFECTED BY PLANT GROWTH REGULATORS

A field experiment was conducted at the Experimental Agricultural Farm of Padova University in Legnaro, Italy, to investigate the effect of a plant growth regulator (trinexapac-ethyl) on temporal changes in species composition of three turfgrass mixtures. Grasses included in mixture 1 were ‘Yorktown III’ and ‘Stravinsky’ perennial ryegrass (Lolium perenne L.), ‘Samanta’ slender creeping red fescue (Festuca rubra ssp. Trichophylla), ‘Darwin’ Chewings Fescue (Festuca rubra L. ssp. Commutata Gaudin), and ‘Julius’ and ‘Eva’ Kentucky bluegrass (Poa pratensis). Mixture 2 consisted of ‘Lucky Selen’ and ‘Debussy’ tall fescue (Festuca arundinacea) and ‘Haga’ Kentucky bluegrass, and mixture 3 included ‘Triman’ and ‘Yorktown III’ perennial ryegrass, and ‘Barimpala’ and ‘Julius’ Kentucky bluegrass. Mixtures were treated with the plant growth regulator trinexapac-ethyl (Primo) from 2006 until 2008 at either half (0.75 kg/ha), the recommended rate (1.5 kg/ha), or one and a half the recommended rate (2.25 kg/ha). Plant growth regulator applications had no effect on species composition when compared to the control. A general change in plant composition over time was observed for all treatments. The temporal shift in species dominance in the mixtures were not influenced by any of the treatments. Over the 3 year research period, Lolium perenne decreased in mixture 1 and 2, while Festuca rubra and Poa pratensis increased. In the third mixture with Festuca arundinacea and Poa pratensis, Festuca remained stable as the dominant species, whereas Poa pratensis increased similarly to mixture 2.