One thing I can think of, but I'm not sure whether you are or not, is
the practice of roguing seed potato crops, thus ridding the crop of
further virus sources. Someone makes a diagnosis based on visual
symptoms and removes the infected plant. Whether there are any reports
on how this affects yield or not - I haven't a clue, though I suspect
that anything that has been published is probably prewar. It's been
going on a long time!
Dave
