Hosts:  Piñon; currants and gooseberries (Ribes spp.) are alternate hosts.

Symptoms/signs:  White columnar sacs (aecia) filled with orange spores occur on all surfaces of piñon needles in the spring. On ribes, uredinia appear as small, round, golden yellow pustules during the summer. Telia, which are waxy and darker orange, develop in late summer on the same ribes leaves.

Biology:  Piñon needle rust must go through five spore stages on two different hosts to complete its one year life cycle. Spores from ribes leaves infect pine needles in late summer to early fall, where the fungus overwinters. Orange droplets form on infected needles in early spring and bright orange aeciospores by late spring. The latter are wind disseminated and infect newly emerged ribes leaves. Urediniospores develop on the ribes and multiply during wet periods. Telia develop in late summer followed by the final spore stage which infects pine needles.

Effects:  Affected needles drop prematurely. This disease is encountered infrequently on piñon, but is very common on Ribes spp.

Similar Diseases:  Coleosporium ribicola on ribes can be mistaken for other rusts of ribes, such as white pine blister rust, Cronartium ribicola. There is another needle rust of piñon in the region, Coleosporium crowellii, which is microcyclic, meaning there is no alternate host. The fruiting structures are more reddish-orange and waxy rather than powdery as in Coleosporium ribicola.

Reference:  106