Considerations for Managing Citrus Black Spot

In Florida, citrus black spot (CBS) is present primarily in commercial groves in five southwest counties (Charlotte, Collier, Glades, Hendry and Lee). The disease can cause up to 60% yield loss in severe situations with little management, researcher Megan Dewdney reported in January.

More commonly though, growers with infestations experience fruit drop levels of 10% to 20% in a minimally managed block, she said. She added that if the fruit is for the fresh market, there are CBS export restrictions to some markets, particularly the European Union. All citrus is vulnerable to CBS, but late-hanging sweet oranges are the most susceptible varieties in Florida.

Dewdney is a University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) associate professor of plant pathology and Extension specialist at the Citrus Research and Education Center in Lake Alfred. She presented a management summary that suggested the following cultural practices can help with CBS:

• Manage leaf litter to enhance the effect of a fungicide program.
• Remove as much dead wood as possible and destroy it on site.
• Practice vehicle and equipment decontamination when leaving affected sites.
• If a CBS management program is reduced or eliminated, the disease will return.

Dewdney also offered suggestions for fungicide timing and use:

• The goal is to maintain coverage on fruit. Because coverage is so crucial, Dewdney recommends using at least 125 gallons per acre and moving the sprayer slowly. 
• Applications should be made a minimum of once per month for best control.
• Start in May if it was dry in April; otherwise start applications in April.

Scouting tips included:

• Wait for color break or about one month before harvest.
• Visit multiple locations in the grove, especially along roads or near staging areas for equipment or fruit trucks.
• Declining trees tend to have more disease.
• Sunny sides of trees tend to express symptoms first.

Learn much more about citrus black spot, including recommended products for control, in the Florida Citrus Production Guide.

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