Melanose

In coastal orchards one of the major factors contributing to fruit blemish is the disease melanose, caused by the fungus, Diaporthe citri. All citrus varieties are susceptible to melanose infection. Melanose can affect trees at any age and damages fruit, leaves, twigs, branches, and in some circumstances, the main trunk of the tree. Damage is superficial and does not affect internal fruit quality. On the fruit, leaves and small twigs, small, dark brown to black spots are produced which are raised and rough to touch. The spots are superficial and can be removed with your fingernail. The incidence of melanose usually increases as trees age and the amount of dead wood in the canopy increases. The melanose fungus also causes a wood rot which occurs when trees are stressed, such as by drought. It causes a cinnamon brown discolouration of bark with a well defined margin between healthy and diseased tissue, often with streaks of yellow gum. The melanose fungus also causes one form of stem end rot of fruit (phomopsis stem end rot).