Greasy Spot

Mycosphaerella citri

Greasy spot symptoms are first noted as pale yellow, slightly raised lesions on the underside of the leaves (Timmer and Gottwald, 2000). Lesions darken with age and eventually become brown to black. On the upper surface of the leaves, lesions are seen as yellowish spots which may also darken eventually. Spots are surrounded by yellow halos. Symptoms differ according to citrus species. Lesions on lemons and limes tend to be more diffuse, less raised, and are not as dark. On oranges and mandarins, which are less severely affected, lesions tend to be more restricted and raised, and are grey to black.

Symptoms on fruit are known as greasy spot rind blotch (Whiteside, 1972). The pathogen invades stomata and surrounding cells forming minute black spots. Adjacent cells fail to lose their chlorophyll as the fruit colours forming a greenish blemish with many black specks. These black specks can occur in splotchy areas scattered on the fruit or involve large areas of the fruit surface. On severely affected fruit, lesions coalesce and become sunken to form large pinkish-brown areas. This disease is most severe on grapefruit, but also occurs on oranges, mandarins and other citrus fruits.

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