Received: 1 April 2025
Accepted: 9 September 2025
DOI: 10.1002/csc2.70179
Crop Science
ORIGINAL ARTICLE S e e d P h y s i o l o g y, P r o d u c t i o n & Te c h n o l o g y
Plant growth regulator effects on seed yield of timothy Surendra Bhattarai1
Hari P. Poudel2
Nicole P. Anderson3
Calvin L. Yoder4,5
1 Department of Plant Sciences, College of
Agriculture, Life Sciences and Natural Resources, University of Wyoming, Laramie, Wyoming, USA 2 Lethbridge Research and Development
Centre, Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada 3 Division of Food Production and Society,
Norwegian Institute of Bioeconomy Research, Ås, Norway 4 SARDA Ag Research, Donnelly, Alberta,
Canada 5 Peace Region Forage Seed Association,
Dawson Creek, British Columbia, Canada Correspondence Calvin L. Yoder, SARDA Ag Research, Donnelly, T0H 1G0 AB, Canada. Email: calvinyoder123@gmail.com. Assigned to Associate Editor Wei Wu. Funding information Agriculture and Agri-Food Canada, Grant/Award Number: J-002132; Peace Region Forage Seed Association
Abstract 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. Plain Language Summary Utilization of stem-shortening plant growth regulators (PGRs) to prevent lodging is a relatively new management practice for forage seed crops in Canada. Timothy is a winter-hardy forage grass with very low soil nutrient requirements, except for adequate moisture. Thus, timothy seed production fields are prone to lodging when nitrogen fertilizer is applied. This study examined the effects of two PGRs, chlormequat chloride (CCC) and trinexapac-ethyl, on plant height, lodging, seed weight, and seed yield in timothy crops. Results indicated that CCC applied at the 2–3 node
Abbreviations: BBCH, Biologische Bundesanstalt, Bundessortenamt, and Chemische Industrie; CCC, chlormequat chloride; PGR, plant growth regulator; TE, trinexapac-ethyl. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. © 2025 The Author(s). Crop Science published by Wiley Periodicals LLC on behalf of Crop Science Society of America. Crop Science. 2025;65:e70179. https://doi.org/10.1002/csc2.70179
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