Citrus black spot (CBS) disease has only been found in five Southwest Florida counties, but that could change as a result of 2017’s Hurricane Irma, a researcher reiterated recently. University of Florida Institute of Food and Agricultural Sciences plant pathologist Megan Dewdney, in a Feb. 24 presentation, said “Irma will haunt us for a while.” She explained that Irma likely moved black spot to new areas. The spread may not be seen for up to five years after the storm, she added.
CBS has so far been detected in Charlotte, Collier, Glades, Hendry and Lee counties. But Dewdney said areas downwind of those counties during Hurricane Irma are “at significant risk of outbreak” and should be scouted regularly for symptoms.
Growers not currently in a CBS survey area who are concerned about the disease should learn to recognize its symptoms and scout for it, Dewdney suggested. They can also contact the Citrus Health Response Program at 863-298-3000 and request a multi-pest survey of their property.
Dewdney suggested CBS scouts wait for color break or about a month prior to harvest and visit multiple locations in the grove. She said the disease tends to be found initially in clusters; multiple trees may be infected in a small area and have asymptomatic trees around them. Particular areas of interest for scouting are along roads or near staging areas for fruit trucks or grove equipment. Dewdney said declining trees tend to have more disease, and sunny sides of trees tend to express symptoms first.
Fungicides recommended for CBS are in the 2021–22 Florida Citrus Production Guide. Dewdney advised growers to alternate copper at the full rate with a strobilurin (Abound, Gem or Headline), a premix or Enable. Premixes are Pristine [succinate dehydrogenase inhibitor (SDHI)], Amistar Top (demethylation inhibitor) and Priaxor (SDHI); they contain a strobilurin. It is best to alternate modes of action. Growers should apply at least 125 gallons per acre and move the sprayer slowly through the grove to provide good coverage, Dewdney said.
All citrus is vulnerable to CBS, but late-hanging sweet oranges are the most susceptible varieties in Florida. Dewdney recommended a minimum of once-a-month fungicide applications for best control. Start applications in May if April is dry, otherwise start applications in April, she said.
Learn more from Dewdney about CBS in this Citrus Industry Tip of the Week.
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