Citrus Extension Black Spot 

Plant Pathology


 

 

History of Citrus Black Spot

Citrus black spot, caused by the fungal pathogen Guignardia citricarpa (sexual stage) and Phyllosticta citricarpa (asexual stage), was first found in south Florida in March 2010. The initial find was contained to a 15 mile area centered in south Florida near Immokalee. By the first week of May, the disease has been found in another location about 14 miles northeast from the original find. It is expected to be found in additional areas when the new harvest season begins in the fall.

Around the world, black spot can be found in Argentina, Australia, Brazil, China, Ghana, Mozambique, Philippines, South Africa, Sub-Saharan Africa, Taiwan and other regions of South America.

 

Fruit Symptoms

Black spot symptoms occur in several forms called hard spot, cracked spot, false melanose and virulent spot which are described below.

Hard spot is the most common and diagnostic symptom. The lesions are small, round, sunken with gray centers and brick-red to chocolate brown margins. Green halos are often seen around hard spot lesions. Fungal structures appear as slightly elevated black dots in the center of lesions. They appear as fruit begins to color where light exposure is greatest.

False melanose is observed as numerous small, slightly raised lesions that can be tan to dark brown. It may occur on green fruit and does not have pycnidia (fungal structures). False melanose may become hard spot later in the season.

Cracked spot has large, flat, dark brown lesions with raised cracks on their surface. It is thought to be caused by an interaction between the pathogen and rust mites. It occurs on green as well as mature fruit and can become hard spot later in the season.

Early virulent spot, also known as freckle spot, has small reddish irregularly shaped lesions. It occurs on mature fruit as well as post-harvest in storage. It 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. Many fungal structures can be found in these lesions.

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

 

Leaf and Stem Symptoms

Leaf and stem symptoms are not as common as fruit symptoms, but can occur when there is insufficient disease control on any cultivar. They are most commonly found on lemons, a very susceptible species.

Lesions begin as small reddish brown lesions that are slightly raised. With age they become round sunken necrotic spots with gray centers and prominent margins that are brick-red to chocolate brown.

 

Regulations

Stipulations for Movement of Citrus Fruit from EAN Regulated Areas for Citrus Black Spot PDF

Citrus Black Spot Federal Quarantine Order PDF

More information will be added as it becomes available. However, for most up-to-date information from regulatory agencies, please contact the Florida Division of Plant Industry 863-298-7777.

 

Spread

• Wind-borne ascospores are forcibly ejected from fungal fruiting bodies embedded in leaves in the leaf litter under trees and are carried by air currents, approximately 75 feet (25 meters) from leaf litter.

• Rain splash may also move spores from infected fruit (conidia) and/or leaf litter (conidia and ascospores), but moves the spores only a few inches (centimeters).

• Live leaves that have latent infections (infections that are not visible) are common means of long distance spread. These often are moved as trash in loads of fruit.

• Infected nursery stock is another potential means of spread. This can occur very easily since these latent infections cannot be seen in otherwise healthy-looking trees.

• Leaf litter movement may be either by wind or human activities

• Humans are the main form of long distance movement


Life Cycle of Citrus Black Spot

 

Diagnostics

If you suspect you may have black spot, please contact your local CHRP office for further diagnostic testing.

 

Management

• Always plant clean, certified nursery stock. Keeping nursery stock clean is much easier with the new covered nursery regulations but black spot is still a threat. This will help prevent movement of black spot and other diseases into newly established grove plantings.

• Increase air flow in grove to reduce leaf wetness where possible. G. citricarpa needs 24-48 hours of leaf wetness for spore germination and infection as do many other fungal diseases.

• Reduce leaf litter on grove floor to decrease ascospore load through enhanced microsprinkler irrigation.

• Fungicides registered for citrus in Florida that have been found effective in other countries:

    •Copper products (all formulations have been found to be equivalent)

    •Strobilurins fungicides currently approved labels are Abound, Gem and Headline

• The best fungicide application method is with air blast sprayer. Aerial applications are not likely to get adequate canopy penetration for control. It is important that the leaves and fruit are covered with fungicide.

• For enhanced coverage, increase the gallons used to 250 gallons/acre for applications to ensure full coverage.

• Strategies for Effective Eradication of Citrus Black Spot in Collier and Hendry Collier

Citrus Black Spot Management 1/9/2013

 

Presentations

Citrus Black Spot (Guignardia citricarpa): Identification, Biology and Control, Megan Dewdney & Natalia Peres (August 2010)

Challenges in the Citrus Black Spot (CBS) Health Management for the Fresh Fruit Market, Eduardo Feichtenberger (August 2010)

Response of FDACS DPI to Citrus Black Spot in Florida, Tim Schubert (August 2010)

APHIS Response to Citrus Black Spot in Florida, Michael Hornyak & Dave Munyan (August 2010)

Citrus Black Spot, Megan M. Dewdney (May 2010)

Citrus Black Spot Diagnostics, Katherine Hendricks and Pamela Roberts (May 2010)

 

Photo Gallery

Click Here for Photo Gallery instructions.

 

Links

Florida Division of Plant Industry Citrus Black Spot Updates (including maps of quarantine areas) website

USDA Press Release-English PDF

USDA Press Release-Spanish PDF

Florida Division of Plant Industry Pest Alert PDF

Fungicide resistance: Why it happens and how it may affect you. Citrus Industry, March 2010 PDF

Citrus black spot. Citrus Industry, January 2010 PDF

University of Florida, Postharvest website

 

Resources

If you would like to obtain laminated identification sheets or copies of the other various educational materials, please contact Jamie Yates, 863-956-1151 ext. 1302 or jdyates@ufl.edu

Citrus Black Spot : No longer an exotic disease PDF

Citrus Black Spot ID Sheet PDF

Citrus Black Spot Management Timing Schedule PDF

Citrus Black Spot Poster for Growers (18 x 27) PDF

Citrus Black Spot Poster for Packinghouses (32 x 26) English PDF

Citrus Black Spot Poster for Packinghouses (32 x 26) Spanish PDF

Packinghouse Citrus Black Spot ID PDF

Quick Reference Guide to Foliar Fungicides PDF

 

Contacts

 
Megan Dewdney, Ph.D. Plant Pathologist 863-956-1151   mmdewdney@ufl.edu
Natalia Peres, Ph.D. Plant Pathologist 813-633-4133   nperes@ufl.edu
Mark Ritenour, Ph.D. Postharvest Physiology 772-468-3922   ritenour@ufl.edu
Pamela Roberts, Ph.D. Plant Pathologist 239-658-3400   pdr@ufl.edu
Florida Multi-County Citrus Extension Agents