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A U.S. Department of Agriculture announcement April 8 confirmed the finding of black spot fungus (Guignardia citricarpa) in a commercial citrus grove in Immokalee, FL. As of May 10, 11 cases of the disease had been confirmed.

Considered an exotic disease, black spot symptoms include dark, speckled spots or blotches on the rinds of citrus fruits. It is an economically significant citrus disease in that it causes early fruit drop, reduces crop yield and renders the highly blemished fruit unmarketable in the fresh market.

While all commercial citrus cultivars are susceptible to citrus black spot, the most vulnerable are lemon and late-maturing citrus varieties like Valencia oranges.

The Florida discovery was made during a routine survey requested by a grower in early March. An inspector from the Florida Department of Agriculture & Consumer Services' Division of Plant Industry's Health Response Program collected a suspect sample from a commercial Valencia orange grove in Florida's Collier County. While the initial laboratory analyses by FDACS-DPI confirmed the black spot finding, subsequent testing by the USDA at the Beltsville, MD, laboratory provided the final confirmation.

This marks the first confirmed find of this fungal pathogen in North America and constitutes a major jump in its geographical range.

Federal and state agriculture officials have joined forces to address the challenges this new citrus disease presents. Rebecca Bech, deputy administrator for APHIS' Plant Protection & Quarantine program, said in the USDA's statement, "We are working in collaboration with the FDACS, the University of Florida's Citrus Research & Education Center and the citrus industry to limit the spread and impact of this disease through swift regulatory actions, education and informed compliance."

The efforts to date include delimiting surveys at arcs around the positive finds at multiple mile ranges, identifying other high-risk areas for the survey, inspecting shipments received at packinghouses and processing plants, inspections at all lemon groves in Florida, and surveying residential areas surrounding the positive find areas.

APHIS has also issued Emergency Action Notices to five groves within the one-mile arc around the initial detection area and to processing facilities that receive fruit from those groves. Such notices specify the requirements for moving fruit, the decontamination treatment requirements for equipment and how leaves and other plant debris remaining in trailers and field boxes are to be treated and destroyed.

"Discovering black spot in a Florida grove is one in a long line of challenges brought on by fair trade," Terence McElroy, department press secretary for the FDACS, told The Produce News. "You can take all of the weather-related problems the agriculture industry has faced over the years, including hurricanes, and still the biggest challenges come from diseases and pests that enter the country on imported products. The federal government, which has the responsibility of protecting our border, cannot possibly inspect every package or piece of fruit that comes in to the U.S."

Mr. McElroy said that copper spray is currently being used on trees that are located in a susceptible range of the black spot find. The effort helps make trees fairly resistant to the fungus. The spray is the same type that is used to help protect trees from citrus canker, which is a bacterial disease.

"But copper spray does not kill black spot on trees that are infected," he added. "A number of fungicides are being studied now, and our agency and growers will be seeking [U.S. Environmental Protection Agency] approval very shortly to use one or more of them in the field."

Despite the many challenges the Florida citrus industry has faced in the past 15 years, when all the ancillary and far-reaching business the industry conducts is added up, it continues to be an approximately $8 billion- to $10 billion-dollar-a-year industry.

"Actual acreage is down from 900,000 to about 600,000 over the past decade, so there has been certainly shrinkage in those terms," said Mr. McElroy. "But prices over the last 15 years have increased. And in terms of efficiency, we're producing as much citrus on less acreage today than we were when acreage was at its peak."

The USDA indicated that a forensic investigation is underway that aims to determine the origin of the black spot infection. The next steps include the appointment of the Citrus Health Response Plan working group to focus on citrus black spot regulations, research and outreach initiatives.

Citrus black spot occurs in subtropical regions of the world with summer rainfall. The disease has been found in Argentina, coastal areas of Australia, Brazil, China, Indonesia, Japan, Kenya, Mozambique, Nigeria, the Philippines and areas of South Africa, Swaziland, Taiwan, Uruguay, Venezuela and Zimbabwe.