Don’t Forget Citrus Black Spot in Florida

Jim Rogers Diseases

While HLB tops the agenda, Megan Dewdney, an associate professor of plant pathology and an Extension specialist with the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS), reminded growers that citrus black spot (CBS) remains a concern. This was the topic of a presentation she made during the Florida Citrus Growers’ Institute held in Avon Park in April.

Citrus Black Spot
Oranges infected with Citrus Black Spot. Emerging pathogens, agricultural threats. Photo provided by Megan Dewdney.

While CBS remains confined to parts of five counties in Southwest Florida, the disease continues to spread. Hurricane Irma in 2017 helped move the disease around, and its effects are still being realized. CBS has latency between infection and symptoms being recognized in groves, so it is still showing up years after the storm.

Every year since the disease was confirmed, scouts from the Florida Department of Agriculture and Consumer Services have identified new blocks infected by CBS. The spread has continued even in years when weather is not conducive for movement. This includes last spring, which was hot and dry.

Growers in areas affected by the disease should scout and take appropriate management measures. “In severe cases, CBS can reduce yields by up to 60%,” Dewdney said. “We’ve not seen that here, but we can commonly see yields dropped by 10% to 20% in a minimally managed citrus grove.”

There are quarantine zones for CBS in Hendry, Collier, Charlotte, Glades and Lee counties. Dewdney noted growers with groves near quarantined areas need to be scouting for the disease. That starts with knowing the symptoms of the disease. Those not confident in scouting for CBS, can contact the Citrus Health Response Program (CHRP) for a multi-pest survey to be conducted in groves.

Scouting should be conducted at color break or about one month before harvest, because that’s when symptoms are easier to spot. Scouts should inspect multiple locations in the grove because CBS tends to cluster in spots, especially early in its infestation. Particular attention should be given to areas near roads or in staging areas in groves where equipment and trucks are moving through.

If CBS is present in groves, fungicide management is important. Dewdney referred growers to UF/IFAS recommendations for CBS management. Those guidelines suggest a program built around alternating a full rate of a copper product with strobilurin fungicides.

“Coverage is key, so at least 125 gallons of water per acre, and go slow through the grove with your sprayer,” she advised. “Maintaining coverage also is important, so you want to be making applications monthly starting in May (through September), unless it was really wet in April. In this case, you should consider moving the first application early into April.”

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Frank Giles

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