Spotting the Symptoms of Citrus Black Spot

Ernie NeffDiseases

citrus black spot
Citrus black spot on Valencia fruit

University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Extension recently provided the following information about identification of citrus black spot (CBS):

Fruit symptoms can be observed around this time of year with the onset of color break and fruit maturity. Growers and agricultural workers should learn to identify the symptoms of CBS even if they are not located in a quarantine zone. Scouting in multiple areas around the grove will allow you to find any areas that may have this disease. There are four fruit symptoms of CBS that growers should scout for:

HARD SPOT
The first symptom is hard spot. The lesions appear on the fruit with the onset of color break and are slightly sunken with a brick-red to brown margin depending on the age of the lesion. A green halo may also be observed surrounding the lesion. The centers of the lesions are necrotic and contain small black dots which are the fungal structures called pycnidia.

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FALSE MELANOSE
The second symptom is false melanose. This can be found on green fruit as well as mature fruit. False melanose is a collection of many small lesions, which range from tan to brown in color and are slightly raised. Pycnidia are not present in these lesions. As the season progresses, false melanose can become hard spot.

CRACKED SPOT
The third symptom is cracked spot. The lesions associated with cracked spot are large and flat and can be found on green and mature fruit. There is a network of cracks throughout the lesions. Cracked spot lesions are thought to be caused by an interaction with rust mite damage and the CBS fungus. This symptom can also turn into hard spot later in the season.

EARLY VIRULENT SPOT
The last symptom is early virulent spot (freckle spot). The lesions on the fruit are small, irregular shaped, sunken areas, which are surrounded by a reddish margin. As these lesions become larger, they can grow together, or coalesce, forming larger lesions. This can lead to virulent spot. Virulent spot can often be found on mature fruit in the grove and during postharvest while fruit is in storage.

Learn where CBS is in Florida. Management information can be found in the 2020-21 Florida Citrus Production Guide.

Source: Citrus from the Ridge to the Valley, November 2020

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