Technical Abstract: Invasive plants are degrading wildlands around the globe by displacing native species, reducing biodiversity, and altering ecological functions. The current approach of applying herbicides to invasive plants in wildlands has not been effective at curtailing their expansion and, in certain circumstances, may do more harm than good. Preventing the spread of invasive species has been identified as an important strategy to protect wildlands. However, few prevention strategies have actually been tested. To evaluate the potential for competitive vegetation to limit the spread of invasive plant species, we established twelve competitive vegetation barriers in front of invasive annual grass, medusahead (Taeniatherum caput-medusae (L.) Nevski), infestations. Desert wheatgrass (Agropyron desertorum (Fisch. ex Link) Schult.) was seeded into plant communities adjacent to the infestations to create the competitive vegetation barriers. Soil nutrient concentrations and the spread of medusahead were compared between where desert wheatgrass was seeded and not seeded (control treatment) three years after treatment. Less medusahead and lower soil ammonium and potassium concentrations in the competitive vegetation barrier than control treatment (P = 0.01) suggest that establishing competitive vegetation increased the biotic resistance of the plant communities to invasion. Medusahead cover and density in the plant communities protected by the competitive vegetation barrier (locales across the barriers from the infestations) were approximately 42 and 47-fold less, respectively, than unprotected plant communities (P < 0.01). This suggests that invasive plant propagule pressure was decreased in the plant communities protected by competitive vegetation barriers. The establishment of competitive vegetation around infestations may be an effective strategy to prevent or at least reduce the spread of invasive plant species.