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 growing conditions are good. In these cases, just before crop planting, farmers often face a tradeoff between the benefits of increased cover crop growth and the drawbacks of reduced soil moisture for cash crop production that season. C/N ratio is balanced with this application. Thick cover crop stands often compete well with weeds during the cover crop growth period, and can prevent most germinated weed seeds from completing their life cycle and reproducing. If the cover crop is flattened down on the soil surface rather than incorporated into the soil as a green manure after its growth is terminated, it