White pine blister rust in the interior Mountain West

White pine blister rust is an exotic, invasive disease of white, stone, and foxtail pines (also referred to as white pines or five-needle pines) in the genus Pinus and subgenus Strobus (Price and others 1998). Cronartium ribicola, the fungus that causes WPBR, requires an alternate host - currants and gooseberries in the genus Ribes and species of Pedicularis and Castilleja (McDonald and others 2006, Zambino and others 2007) - to complete its life cycle. White pine blister rust was discovered in western North America in 1921. It is thought that the disease was accidentally introduced on infected eastern white pine (Pinus strobus) nursery stock shipped to Vancouver, BC from Europe in the early 1900s but the specific details are unclear. Since then, the disease has spread throughout the distributions of most western white pines. Although all of the North American white pine species are susceptible to white pine blister rust (Bingham 1972, Hoff and others 1980), it was once thought that the remote, dry habitats occupied by the noncommercial, high elevation white pines would not support rust establishment. Unfortunately, white pine blister rust can now be found in many of these areas.