Blackberry yellow vein disease (BYVD) is the most important virus disease of blackberry in the Southeastern United States. In order to determine viruses in BYVD-affected plants in Mississippi we tested a total of eighty one symptomatic cultivated and wild blackberries collected from different locations for infections by nine different viruses. All tested viruses were present in diseased samples at various rates, with the exception of Rubus canadensis virus 1. Blackberry yellow vein associated virus is prevalent virus in Mississippi, infecting 70% of tested samples, followed by Tobacco ringspot virus. The second part of this research focused on molecular and phylogenetic studies concerning a putatively new virus species, provisionally referred to as Blackberry virus X and present in approximately 27% of the tested samples. Data generated in this study suggest that BVX is a novel species in the family Betaflexiviridae, with final taxonomic allocation (at the genus level) yet to be determined.