Theresa Badurek, Urban Horticulture Agent, Pinellas County Extension

What is it?

Citrus black spot, Guignardia citricarpa, is a fungal pathogen that affects only citrus plants. This disease creates lesions on the fruit peel that affects both the yield and the appearance of the fruit. The greatest risk for the spread of this disease is that spores are released in the late spring and summer from decaying leaves beneath the trees.

Hard spots caused by Guignardia citricarpa

Why is this important?

Because of its potential to impact the citrus industry it is critical that this is closely monitored and controlled. Until recently the closest infestations of citrus black spot were in Argentina and Brazil. The disease has long been included in the list of threatening exotic citrus diseases but had not been found in Florida. In early March of this year it was first detected in the Immokalee area, and this marked the first detection of the disease in North America. This is extremely important because citrus black spot can reduce the yield of citrus as well as blemish the fruit. According to the United States Department of Agriculture, “it causes early fruit drop, reduces crop yield and renders the highly blemished fruit unmarketable”.

How can I help monitor this?

According to the Florida Department of Agriculture and Consumer Services, Division of Plant Industry, summer and harvest will be good times to observe this. Lesions on the fruit can be used for identification, and you may even observe fruit drop in more severe cases. Click here for more information on disease life cycle and identification:

http://www.doacs.state.fl.us/pi/pest_alerts/pdf/citrus-black-spot-pest-alert.pdf

Other important links:

USDA News Release:

http://www.aphis.usda.gov/newsroom/content/2010/04/fla_citrus_disease.shtml

University of Florida Citrus Disease links:

http://edis.ifas.ufl.edu/pp135

http://edis.ifas.ufl.edu/pdffiles/CH/CH20200.pdf

http://edis.ifas.ufl.edu/pdffiles/PP/PP26400.pdf

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