Trinexapac-ethyl rate and application timing effects on seed yield and yield components in tall fescue

• Trinexapac-ethyl reduced stem length and controlled lodging in tall fescue across six diverse lodging environments.
• Trinexapac-ethyl consistently increased seed yield in tall fescue, but rate of application had no effect on yield.
• Timing of trinexapac-ethyl applications had no effect on seed yield.
• Seed yield increases resulting from trinexapac-ethyl were attributable to greater seed number and harvest index.

Trinexapac-ethyl (TE) has been used for lodging control and seed yield enhancement in several grass seed crop species but little is known about how this plant growth regulator (PGR) performs in tall fescue [Schedonorus arundinaceus (Shreb.) Dumort.]. The objective of this study was to determine how TE application rate and timing influences seed productivity over six diverse lodging environments in Oregon's Willamette Valley. Three field trials were conducted to examine TE effects on seed yield and yield components. Stem length, a key factor in lodging control, was reduced incrementally with increasing TE rate from 17% reduction at 200 g TE ha−1 to a maximum of 39% reduction at 600 g TE ha−1. Lodging was consistently reduced by TE but had no effect on above-ground biomass and panicles m−2. Over environments, TE increased seed yield by an average 40% over the untreated control. However, TE rate or application timing did not differentially affect seed yield across environments. Increases in tall fescue seed yield attributable to TE were the result of increased seed number m−2 and improved harvest index (HI), but not seed weight. A better understanding of TE-induced seed yield increases will aid in improving use efficiency and economy of this important PGR.