Plant growth regulator effects on seed yield of timothy

Timothy (Phleum pratense L.) is a cool-season perennial forage grass species widely utilized for animal feed and fodder in temperate regions of the world. Timothy is one of the main forage grass crops grown for seed in the Peace Region of western Canada. Timothy performs well under well-fertilized and high-moisture soils, but seed production fields are prone to lodging under such conditions. Lodging in grass crops reduces seed production through self-shading, which limits successful pollination, fertilization, and seed fill. In this study, we investigated the effects of two plant growth regulators (PGRs), chlormequat chloride (CCC) and trinexapac-ethyl (TE), on plant height, lodging, seed weight, and seed yield of timothy for 8 site-years. The study encompassed 5 years at one site with crop stands in their first to fifth year of seed production and 3 years at a second site with crop stands in their first to third year of seed production. The PGRs were applied alone (TE and CCC) and in a mix (TE + CCC) at the 2–3 node (Biologische Bundesanstalt, Bundessortenamt, and Chemische Industrie [BBCH] 32–33) and early heading (BBCH 51–52) growth stages. The application of PGRs (TE, CCC, and their mix) at two different growth stages showed a differential decrease in lodging and plant height and an increase in seed yield in all but 1 site year. Among the PGR treatments, CCC applied at the BBCH 32–33 was the most effective in increasing seed yield and economic returns of timothy.