Hijackers, tricksters and deceitful agents, plant viruses are some of the most devious and threatening enemies of seed potato growers in North America. They are the number one cause of seed lots failing to meet the standards necessary to wear the Wisconsin Certified Seed label. How do they do it, you ask? Scientists have studied potato viruses for decades. They are very small micro-organisms that can enter plant cells with the aid of vectors, such as the aphids, but are incapable of multiplying without the help of the potato host’s resources.