White pine blister rust ("Cronartium ribicola") needs two alternate hosts to complete its life cycle. One host is plants in the genus "Ribes". On the blackcurrant, it causes the leaves to become pale and later develop tiny orange pustules and sometimes a yellow filamentous coating on some leaves. The fruit crop is little affected but the leaves fall early and growth is slowed the following year. The other host is any of the white pines, in which it causes serious disease and mortality for the North American species that have not co-evolved with the rust. As a result, the blackcurrant was banned in the United States as a disease vector for much of the 20th century, and even after the federal ban was lifted in 1966, several U.S. states continued their own bans, some of which remain in force today. The effectiveness of these restrictions is questionable, since other "Ribes" species also host the disease, some are native to North America, and others such as red currants and "Ribes uva-crispa" were never banned.