This creates an unsatisfactory product. Many potato diseases are carried in the tubers. Most fungus disease spores are too tiny to be seen and in small amounts will not usually make a potato inedible. But when the tubers are used as seed potatoes, the fungus will begin to spread as the potato plant begins to grow. One infected potato can infect all the other plants in a field.
Viruses are an even more serious problem.
The answers to controlling both problems are two-fold. In Idaho, the majority of seed potatoes used are grown in Montana and North Dakota. If any of these diseases are found, the seed potatoes will not be certified. Late Blight infection and Soft Rot must be below established tolerances. Levels of other defects, such as Hollow Heart and Growth cracks, are also established.