Fatal yellows

Fatal yellows is a severe and often lethal disease affecting various Citrus species, caused by phytoplasmas. These microscopic, wall-less bacteria colonize the phloem tissues of the host plant, severely disrupting the translocation of essential nutrients and photosynthates from the leaves to the roots and fruits.

The causal agents are specialized phytoplasmas that rely on insect vectors for transmission. In nature, the disease is transmitted by phloem-feeding insects, such as leafhoppers and psyllids, which acquire the pathogen while feeding on infected trees and then inject it into healthy tissues during subsequent feeding sessions.

Symptoms of the disease typically manifest as a progressive chlorosis, where the leaves turn distinctively yellow and often become stunted or curled. As the disease advances, the tree experiences branch dieback, a significant reduction in fruit size and quality, and eventually the entire tree undergoes irreversible decline and death.

Environmental conditions play a crucial role in the epidemiology of Fatal yellows, as the population dynamics of insect vectors are heavily influenced by temperature and humidity. Regions with prolonged warm spells support higher activity of these insects, leading to faster and more widespread dissemination of the phytoplasma within citrus orchards.

Management of Fatal yellows is exceptionally challenging because there are no curative treatments for infected trees. Preventive strategies are paramount and include the exclusive use of certified, disease-free nursery stock, the implementation of rigorous insecticide programs to control vector populations, and the immediate eradication and safe disposal of any tree showing signs of the disease.