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,
Cover crop Cover crop A cover crop is a crop planted primarily to manage soil erosion, soil fertility, soil quality, water, weeds, pests, diseases, biodiversity and wildlife in an "agroecosystem" (Lu et al. 2000), an ecological system managed and largely shaped by humans across a range of intensities to produce food, feed, or fiber. Cover crops are an off season crop planted after harvest of the cash crop. The cover crop will grow up to, or into, the winter and may have to be terminated in the spring so as not to interfere with planting the cash crop. Cover crops are of