Tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] is an important forage and turf grass seed crop in Oregon. Use of the stem-shortening plant growth regulator (PGR) trinexapac-ethyl (TE) has gained broad acceptance by tall fescue seed producers in Oregon and elsewhere world-wide as an economical agent of seed yield enhancement through reduction of lodging. Chlormequat chloride (CCC) is a PGR that is marketed in countries outside of the United States for use in grass seed production as a lodging control agent. Trinexapac-ethyl is an acylcyclohexanedione while CCC is an onium-type compound. Results of studies conducted in New Zealand suggested that combinations of TE and CCC PGRs produced seed yields that were greater than with applications of TE alone in orchardgrass (Dactylis glomerata L.) and in perennial ryegrass (Lolium perenne L.).
The objectives of this study were to investigate the potential effects of TE and CCC PGR combinations on lodging control, canopy characteristics, seed yield, and yield components in forage-type ('Fawn') and turf-type ('Spyder') tall fescue. No research has been conducted to date on the effect of combinations of TE and CCC PGR in tall fescue. Furthermore, there has been no research to examine the potential for differences in crop responses to PGRs between forage-type and turf-type cultivars of tall fescue. Field trials were conducted at Oregon State University’s Hyslop Crop Research Farm near Corvallis, Oregon in two years; 2017 and 2018. The experimental design was a randomized block design with a split-plot arrangement of treatments and four replications. Seven PGR treatments were applied at BBCH 32 including an untreated control, 210 g TE ha-1, 1500 g CCC ha-1, 105 g TE ha-1 + 750 g CCC ha-1, 210 g TE ha-1 + 1500 g CCC ha-1, 210 g TE ha-1 + 750 g CCC ha-1, and 105 g TE ha-1 + 1500 g CCC ha-1.
Applications of TE alone controlled lodging in both cultivars while CCC alone did not, and PGR combinations did not provide better lodging control than TE alone. Seed yield was greater in 'Spyder' than in 'Fawn'. Yield was governed by an interaction of cultivar and PGR in 2018, but not in 2017. Yield was increased by 35.5% in 2017 with 210 g TE ha-1 + 750 g CCC ha-1 compared to the control, and by 31% in 2018 with 210 g TE ha-1 + 1500 g CCC ha-1. In 2018, combinations of 105 g TE ha-1 + 750 g CCC ha-1 CCC and 210 g TE ha-1 + 1500 g CCC ha-1 increased yield in 'Spyder' over the control and TE or CCC alone, but not in 'Fawn'. Seed yield of tall fescue grown in Oregon was not increased by CCC alone. Results from this study indicate that PGR combinations produce inconsistent effects on tall fescue seed yield under Oregon conditions.