Blackberry yellow vein disease causes devastating losses on blackberry in the south and southeastern United States. Blackberry yellow vein associated virus (BYVaV) was identified as the putative causal agent of the disease but the identification of latent infections of BYVaV led to the investigation of additional agents being involved in symptomatology. A potyvirus, designated as Blackberry virus Y (BVY), has been identified in plants with blackberry yellow vein disease symptoms also infected with BYVaV. BVY is the largest potyvirus sequenced to date and the first to encode an AlkB domain. The virus shows minimal sequence similarity with known members of the family and should be considered member of a novel genus in the Potyviridae. The relationship of BVY with Bramble yellow mosaic virus, the only other potyvirus known to infect Rubus was investigated. The presence of the BVY was verified in several blackberry plants, but it is not the causal agent of blackberry yellow vein disease since several symptomatic plants were not infected with the virus and BVY was also detected in asymptomatic plants.