be pruned to a certain height that is dependent on a rate of infection determined by researchers; generally pruning is required for Pinus trees up to anywhere between nine and eighteen feet. Pathological pruning, in which all lower branches are pruned regardless of signs or symptoms of infection, may reduce disease instance in white pine tree stands. Furthermore, genetic hybridization testing has been conducted for more than half a century in order to find resistance among strains of the species, and have since successfully introduced resistance into the eastern white pine Importance Of the five needle pines, sugar pine (Pinus lambertiana), eastern white pine (Pinus strobus), and western white pine (Pinus monticola) are the most economically important for timber harvest and nursery stock. In fact, forests of these species represent some of the most valuable land for timber harvest in the US, as they fetch a premium price over related species. While species such as whitebark pine (Pinus albicaulis) and limber pine (Pinus flexilis) are of less economic importance, they too are affected by Cronartium ribicola, as well as other five-needle pine species across the US. In the early 1900s, large outbreaks of C. ribicola infestation in stands of sugar pines, eastern white pines, and western white pines resulted in the observation of apparently resistant trees, asymptomatic in heavily infected areas. By 1950, breeding programs were in place to use these remaining trees as parents to cross and backcross with progeny to develop rust-resistant varieties. There are now resistant western white pine trees available. The notion that eradication of the alternate host Ribes spp. would be an effective means of controlling the causal agent was largely responsible for the federal ban restricting cultivation of Ribes in the 1920s. Until 1966, when the ban was lifted, US breeding efforts in Ribes were essentially halted. Today, although some state and local bans remain in place, Ribes cultivars are slowly gaining popularity and many resistant varieties are commercially available. Pathogenesis Cronartium ribicola is a heteroecious, macrocyclic pathogen on Pinus spp and Ribes spp. Because young pines are smaller and less developed than mature trees, they are most susceptible to the pathogen. In addition, young trees will often die at faster rates following infection because more needles are likely to be located closer to the main stem (trunk) of the tree, where infection results in canker formation that kills vital cambial tissue responsible for