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Publication #PP274

Citrus Black Spot1

Megan M. Dewdney and Natalia A. Peres2

Figure 1. 

Hard spot symptoms on 'Valencia'


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Figure 2. 

Fungal structures (pycnidia) found in hard spot lesions


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Figure 3. 

Severe hard spot symptoms on 'Valencia'


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Fungal Disease

Caused by Guignardia citricarpa (sexual stage)/Phyllosticta citricarpa (asexual stage)

Major Inoculum Source

Airborne ascospores (sexual spores) from leaf litter

Minor Inoculum Source

Conidia (asexual spores) from pycnidia that form on fruit, dead twigs, and leaf litter. The conidia are rain-splash dispersed. Potential problem on cultivars that have young and mature fruit on the tree simultaneously.

Cultivar Suscetibility

All commercial cultivars are susceptible, but late-maturing cultivars and lemons are most vulnerable.

Leaf Symptoms

Rare in well-managed groves; most common on lemons. Older lesions are small, round, and sunken with a gray center, dark brown margin, and yellow halo. Younger lesions are reddish brown with light centers and a diffuse yellow halo.

Fruit Symptoms

Variable. Four main types:

Hard spot (most common and diagnostic)

Small, round, sunken lesions with gray centers with brick red to black margins. Fungal structures appear as slightly elevated black dots. Appears as fruit begins to color where light exposure is highest.

False melanose

Numerous small, slightly raised lesions that can be tan to brown. Occurs on green fruit and does not have pycnidia. May become hard spot later in the season.

Cracked spot

Large, flat, dark brown lesions with raised cracks in their surface. Thought to be caused by an interaction with rust mite. Can become hard spot later in the season. Occurs on green and mature fruit.

Early virulent spot (freckle spot)

Small, reddish, irregularly shaped lesions. Occurs on mature fruit as well as postharvest in storage. Can develop into either virulent spot or hard spot. Virulent spot is caused by the expansion and/or fusion of other lesions covering most of the fruit surface toward the end of the season.

SEVERELY AFFECTED FRUIT CAN DROP BEFORE HARVEST, CAUSING SIGNIFICANT YIELD LOSS.

Other Black Spot Symptoms

Figure 4. 

Cracked spot symptoms on 'Valencia'


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Figure 5. 

Close view of cracked spot with hard spots forming


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Figure 6. 

Small lesions that will likely develop into hard spot


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Figure 7. 

Young lesions on 'Valencia' leaves


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Figure 8. 

False melanose


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Figure 9. 

Leaf symptoms on ‘Valencia’


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Figure 10. 

Early virulent (circled) and hard spot lesions with a close-up of virulent spots


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Footnotes

1.

This document is PP274, one of a series of the Plant Pathology Department, UF/IFAS Extension. Original publication date May 2010. Revised May 2015. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Megan M. Dewdney, assistant professor, Department of Plant Pathology, Citrus Research and Education Center; and Natalia A. Peres, associate professor, Department of Plant Pathology, Gulf Coast Research and Education Center, UF/IFAS Extension, Gainesville, FL 32611.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.