Some common orange tree diseases, which are common to all citrus trees, include citrus greening, citrus canker and citrus black spot. Another disease that occurs in orange trees is sweet orange scab.
Citrus greening is the most common orange tree disease and is the most destructive, because after a tree is infected there is no cure. The disease causes green, misshapen fruit and is caused by the Asian citrus psyllid insect. Citrus canker weakens the orange tree until it is too weak to produce any fruit, while citrus black spot causes dark blotches of fungus to appear on the fruit, making it unfit for sale.
As of 2015, sweet orange scab is more common in Oceania and South America, and the disease causes lesions to develop on the fruit, often resulting in the fruit dropping from the tree.