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Publication #PP281

Citrus Black Spot: No Longer an Exotic Disease... A Manageable Disease in the Florida Citrus Industry1

Jamie Burrow and Megan Dewdney 2

History

  • Citrus black spot was first found in southwest Florida in March 2010.

  • The initial find was contained to a small area centered in south Florida near Immokalee. By the first week of May, the disease had been found in another location about 14 miles from the original find.

  • It is expected to be found in additional areas when each new harvest seasons begins in the fall.

  • Around the world, black spot can be found in Argentina, Australia, Brazil, China, Ghana, Mozambique, the Philippines, South Africa, Sub-Saharan Africa, Taiwan, and Uruguay, among other humid subtropical countries.

  • It is likely to continue to spread slowly.

Citrus Black Spot

  • Caused by the fungus Phyllosticta citricarpa, also know as Guignardia citricarpa.

  • All commercial cultivars are susceptible, but late-maturing oranges (e.g., ‘Valencia’) and lemons are most vulnerable.

  • Affects fruit rind, twigs, and leaves

  • Four main fruit symptom types: hard spot, false melanose, cracked spot, and early virulent spot

  • Most common symptom is hard spot

  • Causes fruit drop

  • Severely affected fruit can drop before harvest, causing significant yield loss.

Hard Spot

  • Small, round, sunken lesions with tan centers and brick-red to chocolate-brown margins

  • Fungal structures appear as slightly elevated black dots.

  • First appears on sunny side of fruit

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 season

  • First appears on sunny side of fruit

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

  • Also known as freckle spot

  • Small, reddish, irregularly shaped lesions

  • Occurs mostly 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 or in storage

Spread

  • Wind-borne spores (ascospores and conidia), rain splash, or movement of infected plant material

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

Figure 6. 

Reprinted by permission from Timmer, L. W., and Duncan, L. W. 1999. Citrus Health Management. American Phytopathological Society, St. Paul, MN.


[Click thumbnail to enlarge.]

Leaf Symptoms

  • Rare in well-managed groves; most common on lemons

  • Can be seen on older leaves

  • 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.

Management

  • Apply fungicides (e.g., copper, synthetic fungicides)

  • Eliminate leaf litter

  • Increase airflow in trees

Grower Resources

  • UF/IFAS Citrus Research and Education Center website www.crec.ifas.ufl.edu

  • Annual Florida Citrus Production Guide

  • Citrus Black Spot identification sheets

  • Citrus Black Spot Management Timing Schedule

  • Packinghouse Citrus Black Spot ID

  • Identification of Early Citrus Black Spot Symptoms

  • Citrus Black Spot Field Identification Pocket Guide

Report Likely Suspects

If you suspect your citrus tree may have this disease, please contact your local UF/IFAS Extension office or the Florida Division of Plant Industry at 1-800-282-5153

Contacts

UF/IFAS Citrus Research and Education Center

Jamie Burrow
Extension Program Manager
863-956-8648

Megan Dewdney, Ph.D.

Plant Pathologist
863-956-8651

UF/IFAS Department of Plant Pathology

Jeff Rollins, Ph.D.
Plant Pathologist
352-273-4620

UF/IFAS Indian River Research and Education Center

Mark Ritenour, Ph.D.
Postharvest Physiologist

772-468-3922

UF/IFAS Gulf Coast Research and Education Center

Natalia Peres, Ph.D.

Plant Pathologist

813-633-4133

UF/IFAS Southwest Florida Research and Education Center

Ozgur Batuman, Ph.D.
Plant Pathologist

239-658-3408

UF/ IFAS Extension Offices with Citrus Agents

Hardee, Hendry, Highlands, Lake, Polk, St. Lucie, Sumter

Websites

UF/IFAS Extension Citrus Agents: http://citrusagents.ifas.ufl.edu

UF/IFAS Citrus REC: http://www.crec.ifas.ufl.edu

UF/IFAS Southwest Florida REC: https://swfrec.ifas.ufl.edu/

Local UF/IFAS Extension Office: http://sfyl.ifas.ufl.edu/find-your-local-office/

For more information, please contact the UF/IFAS Citrus Research and Education Center, Lake Alfred 863-956-1151

Footnotes

1.

This document is PP281, one of a series of the Plant Pathology Department, UF/IFAS Extension. Original publication date February 2011. Revised January 2014 and May 2018. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Jamie Burrow, Extension program manager; and Megan Dewdney, associate professor, Department of Plant Pathology; UF/IFAS Citrus Research and Education Center, Lake Alfred, FL 33850.


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.