Oomycete pseudofungus (Peronospora belbahrii) is a causal of devastating basil downy mildew disease because once infected basil plants are no longer marketable. The host range is limited to basil and hyssop. Coleus was previously considered as host as well, but pathogen causing downy mildew on coleus has been shown genetically different and specified as P. belbahrii sensu lato. Therefore, P. belbahrii is described as a complex species, likely defined by plant host. The P. belbahrii is air-borne and seed-borne pathogen and it does not need a vector for dispersal. The disease was firstly reported from Africa where it is assumed to have originated on sweet basil and 70 years later it was reported from Europe. Currently, basil downy mildew is of pandemic occurrence and the pathogen is present in almost all areas around the world where basil is cultivated. Since the pathogen is transmitted by the seed, there is a high risk of the pathogen spread by the seed trade.