Responses of Intermediate Wheatgrass to Plant Growth Regulators and Nitrogen Fertilizer

Core Ideas Trinexapac‐ethyl reduces height and lodging in wheatgrass.Trinexapac‐ethyl increased grain yield when lodging risk was high.Prohexanedione calcium had no effect on wheatgrass.Trinexapac‐ethyl can reduce risk of yield losses due to lodging. Intermediate wheatgrass (Thinopyrum intermedium; IWG), a new perennial grain crop, has the potential to provide ecosystem services while producing food‐grade grain; however, productivity is currently limited by high rates of lodging. Trinexapac‐ethyl (TE) and prohexadione‐calcium (PC) are widely used plant growth regulators (PGRs) for mitigating lodging and improving seed yield in other grass crops. Our objectives were to determine the effects of the PGRs PC and TE, PGR application rate, and nitrogen (N) fertilizer rate (0, 40, 80 kg N ha−1) on IWG lodging, height, and grain and biomass yields. Experiments were initiated in first‐ and third‐year stands at St. Paul and Rosemount, MN. Few effects of PC on IWG height, lodging, or yields were observed, while TE consistently reduced plant height by 10 to 20% and lodging by up to 20% in a year with high lodging risk. Application of TE to IWG at the recommended rate (437 g a.i. ha−1) or higher rates increased grain yields by 65 to 100% when lodging incidence was high, but did not affect grain yields in years with lower lodging risk. While a negative correlation between lodging and grain yields was observed, nitrogen fertilizer affected IWG grain and biomass yields in only one of five site‐years, and there was no interaction between N fertilizer and PGR effects on IWG. Nonetheless, the PGR TE demonstrated the potential to reduce plant height and lodging, thereby increasing IWG yield potential.