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Cheatgrass (Bromus tectorum L.), a significant weed in the western US, easily inhibits revegetation efforts following ecosystem disturbance. Imazapic is a commonly used herbicide for cheatgrass management, but more information is needed regarding effective application timing for restoration efforts. Three native perennial grasses important for restoration projects include: western wheatgrass (Pascopyrum smithii (Rydb.) Á. Löve), needle and thread (Hesperostipa comata (Trin. & Rupr.) Barkworth), and blue grama (Bouteloua gracilis (Willd. Ex Kunth) Lag. Ex Griffiths). We aimed to determine (1) if native species establishment exhibited a tradeoff between cheatgrass competition and injury from herbicide and (2) if this differed between a pre- or post-emergent application of imazapic at 70 g ai ha-1. A standard replacement series design was used with 5 proportions of each of the three native species (0% or cheatgrass monoculture, 25%, 50%, 75%, and 100% or native monoculture). Three herbicide treatments (no herbicide, pre-emergent, and post-emergent) were compared. The 39 treatments were replicated 5 times in a randomized complete block design. After 9 weeks, aboveground biomass was harvested, dried, and relative yield (RY) indices calculated to assess competitive ability. Both imazapic applications reduced cheatgrass biomass (p<0.05). Western wheatgrass and needle and thread biomass were reduced less by a pre than post application but either timing equally reduced blue grama (p<0.05). Without imazapic, cheatgrass produced more biomass than native species with this difference less pronounced as the proportion of native species increased (p<0.05). RY and RYT values were lower than expected indicating: 1) interspecific competition was more important than intraspecific and 2) mutual antagonism between the species. In situations where cheatgrass may impact restoration efforts, pre-emergent applications of imazapic at 70 g ai ha-1 will reduce cheatgrass with less negative impacts on newly-seeded native grasses than post-emergent. Ensuring sufficient proportions of native species on the site may reduce cheatgrass.