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Citrus Black Spot

Megan M. Dewdney and Natalia A. Peres

 

Figure 1. Hard spot symptoms on 'Valencia'
Figure 1. Hard spot symptoms on 'Valencia' 
Credit: UF/IFAS 

 

Figure 2. Fungal structures (pycnidia) found in hard spot lesions
Figure 2. Fungal structures (pycnidia) found in hard spot lesions 
Credit: UF/IFAS 

 

Figure 3. Severe hard spot symptoms on 'Valencia'
Figure 3. Severe hard spot symptoms on 'Valencia' 
Credit: UF/IFAS 

 

Fungal Disease

Caused by Phyllosticta citricarpa

Minor Inoculum Source

Conidia (asexual spores) from pycnidia that form on fruit, dead twigs, and leaf litter. The conidia are rain-splash dispersed. The conidia are a particular problem on cultivars that have young and mature fruit on the tree simultaneously but can be present and infect any cultivar. The airborne ascospores are not present in Florida. This spore type may become a problem in the future and lead to greater spread of the disease.

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 have reddish brown margins 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 and mature 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'
Figure 4. Cracked spot symptoms on 'Valencia' 
Credit: UF/IFAS 

 

 

Figure 5. Close view of cracked spot with hard spots forming
Figure 5. Close view of cracked spot with hard spots forming 
Credit: UF/IFAS 

 

 

Figure 6. Small lesions that will likely develop into hard spot
Figure 6. Small lesions that will likely develop into hard spot 
Credit: UF/IFAS 

 

 

Figure 7. Young lesions on 'Valencia' leaves
Figure 7. Young lesions on 'Valencia' leaves 
Credit: UF/IFAS 

 

 

Figure 8. False melanose
Figure 8. False melanose 
Credit: UF/IFAS 

 

 

Figure 9. Leaf symptoms on 'Valencia'
Figure 9. Leaf symptoms on 'Valencia' 
Credit: UF/IFAS 

 

 

Figure 10. Early virulent (circled) and hard spot lesions with a close-up of virulent spots
Figure 10. Early virulent (circled) and hard spot lesions with a close-up of virulent spots 
Credit: UF/IFAS 

 

Publication #PP274

Release Date:April 12th, 2023

Related Experts

Peres, Natalia A.

Specialist/SSA/RSA

University of Florida

Dewdney, Megan M.

Specialist/SSA/RSA

University of Florida

Related Topics

  • Critical Issue: Agricultural and Food Systems
Fact Sheet

About this Publication

This document is PP274, one of a series of the Plant Pathology Department, UF/IFAS Extension. Original publication date May 2010. Revised August 2018 and April 2023. Visit the EDIS website at https://edis.ifas.ufl.edu for the currently supported version of this publication.

About the Authors

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

Contacts

  • Jamie Burrow
  • Megan Dewdney