Citrus exocortis is a disease of citrus plants, caused by the Citrus exocortis viroid (CEVd) a member of the genus Pospiviroid within the family Pospiviroidae consisting of a naked single-stranded circular RNA molecule of 246–475 nucleotides. It can causes stunted growth and reduced yields in affected plants. The disease is also sometimes called “scalybutt”. CEVd can also infect tomato plants. The resulting disease is sometimes called “tomato bunchy top disease”. A wide range of citrus species and varieties respond but differ in the time of appearance and severity of symptoms. Majority show classical symptoms of bark shelling and scaling of the rootstock and a decrease in tree vigour leading to stunting and yield reduction.