Bromus tectorum L. (cheatgrass or downy brome) presents a rich resource for soil microorganisms because of its abundant production of biomass, seeds, and surface litter. Many of these organisms are opportunistic saprophytes, but several fungal species regularly found in B. tectorum stands function as facultative or obligate pathogens. These organisms interact dynamically with abiotic factors such as interannual variation in weather, with other soil microorganisms, with their hosts, and with each other to create spatially and temporally varying patterns of endemic or epidemic disease. Five principal soilborne pathogens, Ustilago bullata Berk. (head smut pathogen), Tilletia bromi (Brockm.) Nannf. (chestnut bunt pathogen), Pyrenophora semeniperda (Brittlebank and Adams) Shoemaker (black fingers of death pathogen), Fusarium Link sp. n. (Fusarium seed rot pathogen), and a new species in the Rutstroemiaceae (bleach blonde syndrome pathogen), are known to have sometimes major impacts on B. tectorum seed bank dynamics, seedling emergence, and seed production. These pathogens exhibit niche specialization, so that they are rarely in direct competition. They sometimes interact to increase the total impact on B. tectorum stand structure, which can result in stand failure or "die-off." Die-offs represent areas where B. tectorum has been controlled by natural processes, suggesting that these areas might be suitable targets for restoration. Naturally occurring fungal pathogens that can have a strong negative impact on B. tectorum success have also been considered as candidate organisms for B. tectorum biocontrol using an augmentative mycoherbicidal strategy.