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-lien system Crop-lien system The crop-lien system was a credit system that became widely used by cotton farmers in the United States in the South from the 1860s to the 1930s. Sharecroppers and tenant farmers, who did not own the land they worked, obtained supplies and food on credit from local merchants. The merchants held a lien on the cotton crop and the merchants and landowners were the first ones paid from its sale. What was left over went to the farmer. The system ended in the 1940s as prosperity returned and many poor farmers moved permanently to cities and towns, where