Crop diversity fruit trees and banana plants) are cloned. A single pest or disease could threaten a whole crop due to this uniformity ("genetic erosion"). A well-known historic case was the Irish Potato Famine of 1845-1847, where a vital crop with low diversity was destroyed by a single fungus. Another example is when a disease caused by a fungus affected the monocultured 1970 US corn crop, causing a loss of over one billion dollars in production. A danger to agriculture is wheat rust, a pathogenic fungus causing reddish patches, coloured by its spores. A virulent form of the wheat disease, stem rust,
Crop art mosaic portraits by Lillian Colton are also examples. Her seed portraits of celebrities were exhibited in the strictly defined "Crop art" category at the Minnesota State Fair beginning in 1966. Rules for entry of Crop art allow "only seeds from Minnesota-grown farm crops or cultivated garden flowers, fruits, and vegetables" with no wild plant seeds permitted. Colton continued to teach and make Crop art until her death at age 95 in 2007 (Sheehy 2). A new generation of Crop, or Seed artists, known as the "Postmodern School of Minnesota Crop Art" (Sheehy 90) is continuing this folk tradition. Some of