Plant Suppression and Termination Methods to Maintain Intermediate Wheatgrass ( Thinopyrum intermedium ) Grain Yield

Intermediate wheatgrass ( Thinopyrum intermedium (Host) Barkworth & D.R. Dewey; IWG) is a perennial sod-forming grass undergoing domesticated for use as a dual-use grain and forage crop with potential environmental benefits. IWG plant populations increase with stand age, which has been associated with reductions in grain yields after the second production year, thus management techniques are needed to maintain grain yields over time. We measured the effects of two between-row plant termination methods (cultivation and herbicide application) and two within-row suppression methods (burning and mowing), applied at different IWG physiological stages during the growing season. We measured IWG grain and straw yield, root biomass, and weed biomass. Treatments were initiated after the second year of grain harvest and applied for two consecutive years in southeast Minnesota. Grain yields were highest in production year 2 preceding any treatment application and declined in years 3 and 4 by 82% and 57% compared to year 2, respectively, across all management treatments. Termination methods reduced between-row IWG biomass and grain by up to 82% and 91% compared to the control but had no effect on within-row or total grain yield. Fall burning suppression treatments mitigated the negative effects of some termination treatments on grain yield and increased total straw yield. Spring mowing suppression treatments reduced grain and straw yield by 42% and 34%, respectively, compared to the control. Controls had minimal weed biomass while the termination treatments increased weed biomass, especially termination treatments that included herbicide application. No treatments sustained grain yields, but positive effects of some treatments were observed on total biomass and weeds and could be considered by growers.