Citrus greening is probably the most important disease of citrus in the world. Here we show that citrus greening infection induces a very strong decrease in the amplitude of the electrical potential difference in a citrus tree tissue or in a fruit. The non-disruptive method, consisting of a data acquisition system interfaced with computer and identical nonpolarizable reversible electrodes connected to trees, was used for the measuring of electrical potentials and the detection of citrus greening in a tree’s tissue. The amplitude and time dependence of a registered electrical potential difference in a leaf, stem or fruit is sensitive to a tree’s health. Infected trees have a very low DC signal in comparison with healthy citrus trees. This electrophysiological method permits fast detection of citrus greening in citrus trees and can be used for a detection of other diseases in plants and trees. Monitoring the electrical signaling in higher plants represents a promising method to investigate fast electrical communication during environmental changes.