Pine blister rust, caused by the fungus Cronartium ribicola, also affects Ribes, a genus of currant and gooseberry bushes. Although originally from Siberia and Asia, C. ribicola is now found in Europe and North America where it plagues the forest industry and fruit growers alike.

Introduced along with imported trees over the past 200 years, this disease has been devastating pine ecosystems (and, subsequently, the timber industry) across Europe and North America since 1910. In some regions, white pine, the most seriously-affected pine species, is no longer considered a viable forest tree species.

This fungus has a rather complex life cycle: it takes up to four years to complete, requires two hosts, and involves five different types of spores. Both pine trees and the Ribes berry bushes have to be present in the environment for the fungus species to survive -- pine trees can only be infected by spores that develop on the berry bushes, and the berry bushes can only be infected by spores that develop on the pine trees. Pycniospores and aeciospores are produced on the branches and stems of pines; urediniospores, teliospores, and basidiospores on currant and gooseberry foliage.

There is no cost-effective treatment for this fungus. In the early 1900s, efforts were made to interrupt the fungi's life cycle by passing legislation to eradicate currants and gooseberries, which many farms had started growing. Most of this legislation has now been repealed, however, and interest in the cultivation of these berries has increased considerably over the last few years.

Currently, researchers are trying to develop disease-resistant pine trees in hopes of reintroducing white pine forests that can survive.