Blue mold epidemics in the U.S. usually are initiated by showers of airborne spores from infected fields and wild populations in the Caribbean and Mexico. Wild Nicotiana spp. growing in the southwestern and western U.S. also represent important source areas involved in initiation of epidemics in commercial tobacco areas. Most of the Nicotiana spp. are susceptible to the blue mold pathogen, Peronospora tabacina . On site visits and examination of herbarium samples/records document the widespread occurrence of these species from Texas to the state of Washington. Blue mold occurs on these species as a result of overwintering and/or long-distance transport from Texas and Mexico. Trajectories from western locations document the potential for airborne spores to move from wild species to production areas in the mid-west and eastern U.S. The potential for genetic diversity in the pathogen population is discussed based upon these geographically and ecologically separated source locations.