Technical Abstract: PVY Strains (Other publication listed as a web page with photos for USDA-APHIS) A brief introduction on potato virus Y (PVY) symptom expression in potato for necrotic strains (designated PVYN or PVYNTN). Photos of primary (also called current season) foliage symptoms are included of PVY necrotic and PVY common (designated PVYO) strains in different cultivars. Short paragraphs outline how PVY is spread, diagnosed in lab and visually in field, and how certified seed is used for control of virus.