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 circle circle and declared it authentic before it was revealed that it was a hoax. Inspired by Australian crop circle accounts from 1966, Bower and Chorley claimed to be responsible for all circles made prior to 1987, and for more than 200 crop circles in 1978–1991 (with 1000 other circles not being made by them). After their announcement, the two men demonstrated making a crop circle. According to Professor Richard Taylor, "the pictographs they created inspired a second wave of crop artists. Far from fizzling out, crop circles have evolved into an international phenomenon, with hundreds of sophisticated pictographs now appearing