Spring‐Applied Nitrogen and Trinexapac‐ethyl Effects on Seed Yield in Perennial Ryegrass and Tall Fescue

Abstract

Trinexapac‐ethyl (TE) [4‐(cyclopropyl‐α‐hydroxymethylene)‐3,5‐dioxo‐cyclohexanecarboxylic acid ethylester] is a widely used plant growth regulator (PGR) for lodging control and seed yield enhancement in perennial ryegrass (Lolium perenne L.) and tall fescue [Schedonorus phoenix (Scop.) Holub], but little information is available on interaction of this PGR with spring‐applied N. The objective of this study was to determine how spring‐applied N and TE influenced seed production in perennial ryegrass (180 kg N ha−1) and tall fescue (135 kg N ha−1). Field trials were conducted over three harvest years in both crops. Interaction of spring‐applied N and TE were evident for seed yield in all 3 yr in perennial ryegrass and in 2 yr in tall fescue. The combination of spring‐applied N and TE produced the greatest yields among the treatments tested. Averaged over years, the combination of spring‐applied N and TE PGR increased yield over the untreated control (no spring‐applied N and no TE) by 859 kg ha−1 (126%) in perennial ryegrass and by 538 kg ha−1 (75%) in tall fescue. Responses of other seed production characteristics to spring‐applied N and TE were independent of one another. Spring‐applied N consistently increased aboveground dry weight and seed weight of both seed crops. Other characteristics were inconsistently affected or not affected by N or by TE. Spring‐applied N × TE interaction effects in increasing yield were best explained by an increase in seed number per unit area. Perennial ryegrass and tall fescue seed yield is best enhanced by the lodging control agent TE with recommended rates of spring‐applied N.