EVALUATION OF TRINEXAPAC-ETHYL FOR GROWTH REGULATION OF FIVE COOL-SEASON TURFGRASS SPECIES

Plant growth regulators (PGRs) are becoming important tools for managing turfgrass systems. PGRs offer the potential to reduce vegetative growth and the number of mowings. Two field experiments were carried out in 1999 and 2000 in central Italy (42°57’ N – 12°22’ E, 164 m a.s.l.) on Kentucky bluegrass (Poa pratensis L. ‘Baron’), perennial ryegrass (Lolium perenne L. ‘Numan’), tall fescue (Festuca arundinacea Schreb. ‘Barbizon’), creeping red fescue (Festuca rubra ssp. rubra L. ‘Boreal’) and chewing fescue (Festuca rubra ssp. commutata Gaud. ‘Tatjana’) in order to evaluate the effect of trinexapac-ethyl [4(cyclopropyl--hydroxy-methylene)-3,5-dioxocyclohexanecaboxylic acid ethyl ester], a PGR, on vegetative growth (clipping dry weight). One, two or three applications of trinexapac-ethyl at 0.375 kg a.i. ha^-1 were performed from May to July. Untreated controls were included in a split-block design with 3 replicates. All the five species showed a vegetative growth reduction just after each PGR application, but then they showed a different growth recovery ability. Trinexapac-ethyl application did not significantly reduced cumulated clipping dry weight in perennial ryegrass and creeping red fescue. Two PGR applications were needed to affect vegetative growth in Kentucky bluegrass (-40%), tall fescue (-33%) and chewing fescue (-21%). Three applications did not show significant differences in comparison to two applications.