How to Manage Pests

Pests in Gardens and Landscapes

Alternaria rot—Alternaria citri

Alternaria rot is a fungal disease that affects mainly navel oranges and lemons. Fruit infected with Alternaria change color prematurely. The decay is softer on lemons than on oranges and develops mostly during storage. On navel oranges, the disease is also called black rot, and results in dark brown to black, firm spots or areas at the stylar end or in the navel. If you cut the fruit in half, you can see the rot extending into the core.


Healthy, good-quality fruit are more resistant to Alternaria rot than stressed or damaged fruits, especially oranges with split navels. Preventing stress by maintaining a good fertilization and irrigation program can reduce the incidence of splitting and Alternaria rot.

Alternaria infects the navel of oranges

Alternaria rot
Alternaria rot in the core area

Statewide IPM Program, Agriculture and Natural Resources, University of California
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