rust, in botany, name for various parasitic fungi of the order Uredinales and for the diseases of plants that they cause. Rusts form reddish patches of spores on the host plant. About 7,000 species are known. Some grow entirely on one plant; others require two hosts, plants of two species, in order to complete their life cycles. 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. Black stem rust Puccinia graminis is one of the most destructive to wheat, rye, and other grasses; barberry is an alternate host. Rusts attack all cereal crops and many fruits, vegetables, forage crops, ornamental plants, and forest trees. Rusts are hard to eradicate; control measures include the use of rust-resistant varieties of seed and the elimination of alternate hosts in agricultural areas. Rusts are classified in the kingdom Fungi, phylum (division) Basidiomycota, order Uredinales.

blister rust: see rust.

Rust Belt or Rustbelt, economic region in the NE quadrant of the United States, focused on the Midwestern (see Midwest) states of Illinois, Indiana, Michigan, and Ohio, as well as Pennsylvania. The term gained wide use in the 1970s as the formerly dominant industrial region became noted for the abandonment of factories, unemployment, outmigration, the loss of electoral votes, and overall decline. Since the 1960s, manufacturing cities throughout the Great Lakes region and in the Northeast have suffered a decline in population and economic strength as manufacturers relocated, primarily to the Sun Belt, overseas, or more recently, to Mexico. Meanwhile, the nation as a whole has shifted toward a service economy. Detroit, although still one of the world's largest manufacturing centers, has been especially hard hit and unable to reduce its dependence on the manufacturing sector. Suburban flight induced by the decline of the central city has been dramatic in large cities such as St. Louis and Cleveland, as well as smaller cities like Gary, Ind., and Akron, Ohio. By the 1980s, the economy of some Rust Belt cities had noticeably improved after the introduction or expansion of non-manufacturing industries. Pittsburgh, initially devastated by cutbacks in its steel industry as early as the late 1950s, has since emphasized its role as a center for research and development and finance.