Alfalfa Mosaic Virus
Alfalfa mosaic virus (AMV) is in the genus Alfamovirus and is spread by aphids.
Yellow mosaic or calico patterns occur on the foliage. Some strains of AMV can cause severe stunting of plants and tuber necrosis. Sometimes corky or brown areas will develop in potato tubers.
The virus is commonly found in alfalfa. Aphids feed on infected alfalfa, acquire the virus, and transmit it to healthy potato plants. Aphids need to feed on another infected plant to spread the disease again. The virus is not seedborne in potatoes.
Insecticides to control aphids will be of limited help. The best management option is to avoid planting potatoes close to alfalfa fields.