Black Spot Scouting and Control

“The most important time to scout for black spot is when the fruit begin to change color,” said University of Florida Institute of Food and Agricultural Sciences plant pathologist Megan Dewdney. She has seen color change for Valencia oranges, the most commonly infected variety, from December to March. But she added it is usually late-February to early-March when citrus black spot symptoms are seen on Valencias.

Dewdney said scouting for black spot “would give you an indication of how much disease you have in your grove and what you need to be planning for in the next season.” Symptoms of black spot include hard spot, cracked spot, fungal structures and more.

“When the temperatures are a bit cooler … during rain events, we probably are seeing some infection occurring, but it’s going to be happening a little bit more slowly than the spores that we see coming in the summer months,” Dewdney said.

She recommended a multi-pronged management approach for groves with citrus black spot. “To assist your fungicide application, you should probably be trying to reduce the innoculum in the leaf litter,” she said. Dewdney also recommended hedging and pruning to remove dead wood in the grove. “You need to be on a monthly fungicide application program from early May to probably late September,” she added.

Citrus black spot was discovered in southwest Florida groves in 2010. It is mostly confined to the Gulf citrus-growing region. Citrus black spot is a fungal disease marked by dark necrotic spots or blotches on the rinds of fruit. The disease causes early fruit drop and reduces crop yields. It can be spread by wind, rain, leaves and human movement.

Hear more from Dewdney’s interview with Citrus Industry magazine Editor Tacy Callies. The interview was conducted after Dewdney’s Citrus Expo presentation in August.