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,
High plains disease for the wheat curl mite. High plains disease also may occur on barley, oats and rye, and on drooping brome "Bromus tectorum" and yellow foxtail "Setaria pumila" grasses. An ELISA test is available to detect high plains disease. Infection can be avoided by elimination of volunteer crop and wild host plants prior to planting. Resistant varieties of maize exist. High plains disease High plains disease is a viral disease afflicting wheat and maize. It is caused by the negative-sense ssRNA virus wheat mosaic virus. Symptoms are similar to wheat streak mosaic virus, with leaf veins showing yellow flecks and streaks,