Trinexapac‐Ethyl Effects on Red Clover Seed Crops in Diverse Production Environments

Trinexapac‐ethyl (TE) plant growth regulator (PGR) effects on diploid red clover (Trifolium pratense L.) seed production were investigated in two diverse environments, Canterbury (CA), New Zealand (NZ), and Willamette Valley, Oregon (OR). Five TE rate (250 and 500 g a.i. ha−1) and timing [Biologische Bundesanstalt, Bundessortenamt, and CHemische Industrie (BBCH) growth stages 32, 51, 32 + 51] treatments and an untreated control were examined at six on‐farm sites in OR and one experimental site in CA in 2011 and 2012. Seed yield was increased across CA and OR production environments with 500 g ha−1 TE applied at BBCH 32 (15%, CA‐2011; 9%, OR‐2011; 13%, OR‐2012). Split applications of 500 g ha−1 TE (BBCH 32 + 51) improved seed yield by up to 13% in OR but had no effect in CA. Seed weight was generally inversely related to yield; TE treatments that produced the highest yield also had the lowest seed weight and thus did not contribute to TE‐induced yield improvement. Increases in inflorescences m−2 with TE ranged from 26 to 62% in all environments. Coupled with other measured effects of TE on flowering and stem production, these may have been contributing factors to seed yield enhancement by TE. Crop height was consistently reduced by TE across CA and OR environments but aboveground crop biomass was not affected by TE. The timely use of TE PGR is a practice that has broad applicability in red clover seed production across CA and OR environments.