Citrus black spot can make fresh-market fruit unsalable.
Citrus black spot can make fresh-market fruit unsalable.

If there’s any good news to be found in the citrus black spot saga, it’s that the disease hasn’t made much progress over the past year.

First detected in southern Florida during the 2010 spring, the fungal disease as of mid-July remained confined to parts of Collier County, where it first was detected, and Hendry County, says Megan Dewdney, plant pathologist and Extension specialist at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center at Lake Alfred.

Nearly all of the oranges in the affected areas, which are under quarantine by the U.S. Department of Agriculture, are grown for processing, she says. Since the disease does not affect juice quality, it typically won’t affect processing fruit although it can cause yield losses.

It’s a different story for fresh-market fruit. Citrus black spot’s most common symptom is hard spot, which is characterized by small, round sunken lesions with tan centers and brick-red to chocolatebrown margins. Those spots and lesions can render fruit unsalable for fresh market.

Since so little fresh-market fruit is grown in the area, disruption to the industry has been minimal, she says.

In addition to oranges, the disease can affect grapefruit, lemons, tangerines and tangelos.

It’s spread by windborne spores from leaf litter on the orchard floor, rain splash or movement of infected plant material.

Exports unaffected

The disease has not yet affected exports, says Peter Chaires, executive vice president of Florida Citrus Packers in Maitland.

“There have not been any requests for movement of that fruit for export up to this point,” Chaires said in mid-July.

A protocol is in place that could allow exports from the quarantine area.

A grove can be surveyed for signs of the disease, and if it is found to be free of CBS, a harvest permit can be issued, he says.

Fruit would be inspected again at the packinghouse “to double verify that the fruit is free of citrus black spot,” Chaires says.

Chaires agrees with Dewdney that “it does appear to be very slow moving.” “It’s having a minimal effect on our industry,” he says.

“But that doesn’t mean that we’re not taking the disease seriously.”

Everglades Harvesting and Hauling Inc., based in La Belle, grows oranges for processing and was the first to have the disease identified, says president Paul Meador.

However, over the past year, Meador approached the problem aggressively, alternating between strobilurins and copper, and has gotten some control.

“I’m optimistic that we’ll keep it in check for some time to come,” he says.

Some of the trees that showed infection last year don’t show it this year, Meadow says. However, some new trees are showing infection.

“Overall numbers are unchanged from years past,” he says.

Research currently is being conducted on the disease, workshops have been held and experts have been brought in to speak about the issue from countries, such as Brazil, that have suffered substantial negative effects, Chaires says.

“The fact that it’s in very limited areas is encouraging,” he says.

Two defenses

To fight CBS, growers can turn to two chemical classes of fungicides—coppers and strobilurins, or strobis, Dewdney says.

“Copper by itself is adequate, but it’s not the best, by a long shot,” says Henry Yonce, president of KAC Agricultural Research Inc. in DeLand.

The strobilurins Headline, Abound and Gem have worked best so far, he says. They all are in the same family and seem to have the most activity on CBS.

Quadris Top, a fungicide from Syngenta Crop Protection, also is looking good. Yonce says copper can be used as a rotation.

Dow AgroSciences’ Enable, which contains the active ingredient fenbuconazole, may have chemical activities that would make it a rotational partner with strobilurins.

But most growers wouldn’t use it as a mainstay to fight the disease, he says. “It may add enough activity to the copper to be useful,” Yonce says.

The industry continues to look at alternatives. The compound Pristine, a premix of pyraclostrobin and boscalid from BASF, is labeled for citrus and has activity against citrus black spot. But it is not yet labeled for the disease.

The company hopes to have it labeled for CBS no later than the beginning of next season, says Joe Mitchell, a Tampa, Fla.- based technical services representative for BASF Corp.

Yonce says other compounds also are being evaluated, but no decisions have been made to label them for citrus.

Mechanical sweeper

Meantime, grower Maury Boyd, president and an owner of McKinnon Corp., a family-owned business in Winter Garden, Fla., came up with his own method of dealing with CBS.

He had a sweeping machine built that attaches to a tractor and clears leaf litter from groves before it has a chance to spread the disease.

The disease was detected through surveys in one of his groves near its epicenter, and Boyd removed about a half dozen weak, blighted trees and waited for more signs of CSS.

“We never had any more positives,” he says.

Boyd also cleared leaf litter from two or three rows with his custom-built machine, but he has sidelined it for now, until the disease turns up again.

Boyd, who gained renown by developing his own nutritional program to fight citrus greening disease, also added the fungicide Headline to fight citrus black spot.

“So far, we’re coming up clean,” he says.

Boyd has avoided using copper in his groves because he says too much of it can interfere with root systems.

“Copper brings you trouble,” he says.

Boyd still is concerned about CBS.

“But after two years of still being negative, I’m not quite as concerned,” he says.

Citrus black spot was not as much of a problem this year as it was the year before, Yonce says.

That may have been due to less rainfall during the spring than the previous year as well as to growers controlling leaf drop and implementing good sanitation practices in the groves, he says.

“Keeping the floor free of trash seems to have helped where black spot was a problem,” Yonce says.

More information about citrus black is available at www.citrusblackspot.org.