Performance of trinexapac-ethyl on Lolium perenne seed crops in diverse lodging environments

• Application of trinexapac-ethyl plant growth regulator reduced stem length and controlled lodging in perennial ryegrass across nine diverse lodging environments.
• Trinexapac-ethyl consistently increased seed yield and harvest index in perennial ryegrass.
• Timing trinexapac-ethyl applications between BBCH stages 32 and 51 produced the best seed yield results.
• Seed yield increases resulting from trinexapac-ethyl application were attributable to a greater number of seeds spikelet−1 and improvements in seed set.

Application of trinexapac-ethyl (TE) plant growth regulator (PGR) for lodging control in perennial ryegrass (Lolium perenne L.) is a widespread practice, but information on how this PGR increases yield is limited. The objective of this study was to determine how TE application rate and timing influences seed productivity over nine diverse lodging environments in Oregon's Willamette Valley. Four 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 rate of TE to a maximum of 28%. TE consistently reduced lodging but had no effect on the seed yield components spikes m−2, spikelets spike−1, and florets spikelet−1. Over environments, TE increased seed yield by an average 43% over the untreated control at 400 g ai ha−1 TE. Best seed yield results across environments were attained with TE applied between BBCH 32 and 51. The number of seeds spikelet−1, seed mass spikelet−1, and seed set were increased by TE. TE-induced seed yield increases were attributable to increased seed number m−2 and improved seed set, 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.