Citrus Black Spot1

Megan M. Dewdney and Natalia A. Peres 2

Figure 1. Hard spot symptoms on 'Valencia'
Figure 1.  Hard spot symptoms on 'Valencia'

Figure 2. Fungal structures (pycnidia) found in hard spot lesions
Figure 2.  Fungal structures (pycnidia) found in hard spot lesions

Figure 3. Severe hard spot symptoms on 'Valencia'
Figure 3.  Severe hard spot symptoms on 'Valencia'

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 on 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 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 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'

Figure 5. Close view of cracked spot with hard spots forming
Figure 5.  Close view of cracked spot with hard spots forming

Figure 6. Small lesions that will likely develop into hard spot
Figure 6.  Small lesions that will likely develop into hard spot

Figure 7. Young lesions on 'Valencia' leaves
Figure 7.  Young lesions on 'Valencia' leaves

Figure 8. False melanose
Figure 8.  False melanose

Figure 9. Leaf symptoms on 'Valencia'
Figure 9.  Leaf symptoms on 'Valencia'

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

Footnotes

1. This document is PP274, one of a series of the Plant Pathology Department, UF/IFAS Extension. Original publication date May 2010. Revised August 2018. Visit the EDIS website at https://edis.ifas.ufl.edu.
2. 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.

Publication #PP274

Date: 2018-08-21
Dewdney, Megan M
Peres, Natalia A
Citrus REC - Lake Alfred
Plant Pathology

Related Topics

Fact Sheet

Contacts

  • Jamie Burrow
  • Megan Dewdney