Diseases, particularly viral diseases, are a major problem in vegetatively propagated crops and those are almost all that we grow. I do the best management that I can to detect and eliminate disease, but it is not nearly enough. Every year I learn a little more and get a little better, but eradicating disease from the crops that we sell is a long term process. Most of them have probably been carrying viruses for decades.
I do my best to eliminate any varieties that are obviously and seriously sick and that have depressed yield or other symptoms that make them undesirable. The lack of any mention about disease is not an indication that the variety isn’t carrying one; it just means that I don’t know. We have now added a Phytosanitary Info tab to the product description that lists the virus testing results for each variety, so you can at least see what has been tested.
If you are concerned about viruses, the best practice would be to grow from true seeds instead of roots/tubers. I can’t even guarantee you that true seeds carry no viruses, but the likelihood is much lower and we take precautionary steps with our true seeds like heat treatment and surface sterilization to reduce the risk. The growing guides each have a disease section that discusses pathogens of importance for that species and also notes which may be able to transmit through seed.
I am in the process of moving to a growing system in which I grow tubers for planting in a screen house. I perform most testing on those parent plants. If a variety has a Phytosanitary Info tab, the information presented there is a record of testing performed on the parent plants. I simply replant tubers from those parent plants in the screen house as long as they continue to test clean. If any should turn up a positive result, then I can produce new plants from tissue culture to replace them. I don’t test plants in the field unless I see symptoms, so it is possible for varieties that we sell to pick up diseases. This way of growing is intended to reduce the incidence of disease, not to eliminate it entirely. There are some viruses that are established in our area and probably aren’t possible to eliminate entirely. The potato viruses Potato Leafroll Virus and Potato Virus Y are two examples of this. They periodically turn up in the field even though I have worked very hard to eliminate any sources. This is an endeavor in which we struggle against nature, but never really win. I’m seeking improvement, not perfection.