Phytoplasmas are phytopathogenic bacteria from the class Mollicutes. Cereal diseases caused by these microorganisms contribute to serious economic losses. Infected plants change the colour of their aboveground parts and are stunted. Bacteria also damage the root system and cause plant necrosis. The ears are deformed, which leads to sterility and reduced grain yield. The disease can cause on average about 50%, and in some cases up to 90% loss in yield. Wheat, oats and barley are susceptible to phytoplasmas from the ribosomal group 16SrI. Bacteria from ribosomal groups 16SrI and 16SrXII infect maize. Phytoplasmas are transmitted to cereals by insects, mainly species representing the Cicadellidae family, e.g. Psammottetix striatus (L.), Dalbulus maidis (DeLong & Wolcott), Macrosteles laevis (Ribaut) and the Cixiidae family e.g. Reptalus panzeri (Low). In addition, many studies have suggested that wild Poaceae plants may be a reservoir of phytoplasmas in the environment. The occurrence of diverse phytoplasmas in Poaceae species worldwide indicates an ongoing threat towards cereal crops in Europe.