Symptoms of PVY are variable depending on the host cultivar and virus strain (there are many different strains of the PVY virus).
Crops are at their most vulnerable at emergence. After about four weeks the plants begin to display what is called 'Mature Plant Resistance'. This makes virus transmission more difficult and this resistance increases as the plant gets older. However, this resistance does not mean the transmission will not occur, just that it is less likely. The crop is again more vulnerable to virus spread if there is regrowth after desiccation.
Some cultivars have more natural virus resistance than others. Growing one of the more resistant seed varieties would reduce the risk of virus transmission.
Due to the non-persistent nature of PVY, it is unlikely that aphids will bring the virus into your crop. This small risk is increased however if you have ware crops close to your seed crops. Ware crops generally have a higher incidence of PVY present and it is possible for aphids to transmit this to nearby seed crops.
Secondary tuber-born infections are the most common symptoms seen in the field. General symptoms of secondary infection include;
Severe symptoms consist of dark brown, dead areas in stems of nearly mature leaflets. The terminal leaflets may show severe necrosis, and in many cases, all leaflets are infected. Infected leaflets may eventually roll downward giving the plants a dropping appearance.
Primary infection (current season, transmitted by aphids) is often symptomless or results in very mild symptoms as described above.
Symptoms For Different Strains Of PVY Virus