These microorganisms (phyto = plant) grow as parasites in the leading tissue (phloem) of plants. They are similar to bacteria, but unlike bacteria they do not have cell walls, but are surrounded by a flexible cell membrane. Therefore their shape is irregular and can be oval, oblong or multiform. In contrast to viruses, they are capable of independent reproduction. They are so tiny that they can no longer be seen in light microspops. They were first discovered in 1967 in connection with research into the causes of yellowing diseases.
Phytoplasmas colonize the sieve tubes and the cells adjacent to the phloem. They cause abnormal changes in the host plants and in the final stage they cause fatal changes. These are yellowing, shoot shortening, leaf deformation and broom growth. In some plant species they green the flowers, which take the form of leaves. Phytoplasmas are transmitted by insects, such as cicadas. This causes various vine diseases such as flavescence dorée (golden yellowing), blackwood disease, grape wilt and yellowing (grapevine yellows). Phytoplasmas are classified as quarantine organisms in the EU because of their dangerousness. They are controlled quite successfully with hot water. See also a complete list of all diseases and pests under vine enemies.