to attack by other agents, including bark beetles." Disease cycle Cronartium ribicola has two obligate hosts: Pinus spp and Ribes spp. Five-needle pines (Pinus spp.) are infected in the fall by basidiospores that have spread under cool, moist conditions from the alternate host, currants and gooseberries (Ribes spp.), and germinated on needles to enter with germ tubes through open stomata. Young pines are most susceptible and will die at faster rates following infection. A mycelial network then spreads through the needle and into intercellular space in the inner bark, resulting in the formation of a blister rust canker. Spermagonia are produced at the margins on the canker and give rise to spermatia in the following spring. Once spermatia have fertilized receptive hyphae in the Pinus spp. host, aecia are formed within a year, appearing as white blisters before rupture reveals the orange or yellow aeciospores within. The wind-blown aeciospores infect Ribes spp. and the fungus quickly develops uredia in less than a few weeks. Uredospores produced in this stage spread to infect other parts of the same host or other Ribes spp. hosts in the area. Next, telia are developed on the abaxial (lower) surface of leaves, where teliospores germinate to give rise to basidiospores that will complete the disease cycle by infecting Pinus spp. hosts. Hosts and symptoms As is common among rusts, the life cycle of Cronartium ribicola includes two host species and goes through five spore stages. This life cycle is termed heteroecious. In the specific case of Cronartium ribicola, the aecial host of this pathogen is the white pine (Pinus subgenus Strobus, family Pinaceae) and the telial hosts are those of the genus Ribes, specifically currants and gooseberries. Species of both telial and aecial hosts have varying levels of resistance or immunity to infection. On the aecial host, the first signs of C. ribicola are yellow or red spots on the Pinus needles, but these are small and can be difficult to see; more visible symptoms on the aecial host includes perennial cankers which appear on the branches within two years of infection. Looking at the infected plant as a whole, the Pinus will appear chlorotic, and stunted with dead branches or tops that turn a bright red color. On the other hand, the telial host, Ribes, can contract yellowish chlorotic leaf spots, but is otherwise not significantly impacted. The signs of C. ribicola on Ribes,