Rusts form reddish patches of spores on the host plant.
About 7,000 species are known. Cedar rust, for instance, grows on cedar and on apple trees, needing both for development. Blister rust of pine grows on pines and either currant or gooseberry bushes. Rusts attack all cereal crops and many fruits, vegetables, forage crops, ornamental plants, and forest trees. Basidiomycota, order Uredinales.