nepoviruses, group of 13 virus diseases which are spread from plant to plant by the feeding of nematodes (microscopic worms) on roots. They also have in common a polyhedral structure, hence the name ‘nepovirus’: ‘ne’ for nematode and ‘po’ for polyhedral. Such diseases can be very destructive and almost impossible to control. This is because the virus can survive for years in nematodes and root fragments even after all infected vines have been removed. So, even if a new, supposedly virus-free, vineyard is planted, it will quickly become infected by the nematode feeding. Among the important virus diseases in this group are fanleaf degeneration, tomato ringspot, and tobacco ringspot.