HAINES CITY — Florida citrus growers already struggling with the costs of controlling the fatal citrus greening disease face a new economic threat from black spot, a fungal disease discovered last month in Immokalee.
Once black spot spreads across Florida — which appears inevitable, although it could take many years — growers face increased production costs and smaller harvests because the disease leads to premature fruit drop. The disease also could lead to another ban on sales of fresh Florida citrus fruits in other citrus-producing states, notably California, and other countries in an effort to keep the disease out.
"It seems like we can't catch a break right now," said G. Ellis Hunt Jr., president of Hunt Bros. Inc., a family citrus grower and fresh fruit shipper in Lake Wales. "Most growers are up against the wall on the cost of production. Nobody can stand additional costs right now."
An unidentified Immokalee grower reported unusual black spotting on his late-season Valencia oranges last month, said Denise Feiber, a spokeswoman for the Florida Department of Agriculture and Consumer Services.
A March 28 "tentative analysis" by the state Agriculture Department confirmed black spot, she said. The department is waiting for the U.S. Agriculture Department to confirm that finding before releasing an official announcement.
But tests done by the University of Florida's Citrus Research and Education Center in Lake Alfred and the Gulf Coast Research and Education Center in Balm also found fruit infected with black spot, said Megan Dewdney, an assistant professor of plant pathology at Lake Alfred, who performed one of those tests.
"The chances of a false positive are very low," said Jim Graham, a soil microbiologist at Lake Alfred. "This is not a gray area."
Dewdney and Natalia Peres, the assistant professor of plant pathology at the Balm center who also tested the infected fruit, agreed black spot has likely established itself in Florida even though only one grove has tested positive.
"I don't think this arrived last month," Peres said. "It takes time for (the disease) to build up and to see symptoms. Now that we know what we're looking for, I think we'll find other cases."
The disease gets its name from the black lesions it leaves on oranges, grapefruit, tangerines and other citrus fruit. Although the lesions don't affect the juice, they make it all but impossible to sell the fruit on the fresh market.
Juice processors buy 95 percent of Florida's oranges, the state's largest crop, and about 60 percent of grapefruit, but 70 percent or more of tangerines are sold as fresh.
The disease spreads mostly through dead leaves, which emit thousands of airborne spores when they get wet.
The problem is compounded when dead leaves still attached to harvested fruit blow off during transport.
As with citrus canker, also spread by infected plant material, the risk could be lessened by requiring tarps over the truckloads of citrus, Graham said, but that would not eliminate the risk entirely.
Researchers say they can't say how fast black spot will spread in Florida until state agriculture officials determine how far it has spread already.
Surveyors have inspected groves within 3 miles of the Immokalee grove, Feiber said. It hoped to complete 5 miles by the end of this week.
The researchers said they don't have enough scientific data on black spot in other countries and that the disease may act differently in Florida.