Potato viruses reside in the sap inside the vascular tissue (phloem) and arise from seed tubers into the vine and tubers. They can be transmitted between plants by a mechanical or an insect vector. The usual insect vectors for potato are aphids and leafhoppers. Viruses are responsible for generational loss of plant vigor and tuber yield from one year to next, "running out." The best control for all of the viral-induced diseases is through meristem tissue culture, and year-to-year certification inspection and screening. An immunological test, ELISA, is necessary to identify viruses in the sap and is usually done through the state's certification association. Secondary methods of control are roguing, i.e., removing visibly infected plants, insect control and weed control. Viral diseases primarily play a roll by reducing tuber size and number, i.e., yield, and seed tuber performance. Tuber quality is not an issue in the fresh market, but in the case of leaf roll, can be a major issue in processing, fry and chip markets. Tubers grown for seed may be de-certified due to viral content. Viral diseases that have appeared in Nebraska are leaf roll, mild mosaic, rugose mosaic, and calico.
For a quick guide and comparison of viral-type diseases, refer to Table.