Some tomato growers around Tampa may be getting unwanted help from their own equipment. A University of Florida field study suggests that routine tractor-mounted fungicide sprays can kick the bacterial spot pathogen up into the air and carry it well beyond infected tomato plants, potentially pushing the disease through an entire field instead of shutting it down. The findings land squarely on the radar of Florida fresh-market tomato growers who rely on heavy spraying during wet, humid weather.
At the UF/IFAS Gulf Coast Research and Education Center, doctoral student Renzo Ramirez deliberately infected tomato plants, then used a tractor-driven sprayer and air samplers to mimic fungicide applications and track how far the bacteria could travel. Under typical spring conditions, he detected the pathogen as far as 24 feet from infected plants and up to 15 feet above the ground, according to the Tampa Free Press.
Aerosols and Overhead Irrigation
UF/IFAS researchers had already shown that the bacterial spot organism can ride tiny water droplets produced by overhead irrigation during greenhouse transplant production, a setup that lets the pathogen move quickly among tightly packed seedlings. As outlined by UF/IFAS, wind-driven rain and irrigation droplets are also well-established routes for moving the disease from field to field.
Why Fungicide Sprays Can Backfire
UF plant pathologist Gary Vallad has been telling growers that fungicides often do not control bacterial pathogens because of resistance, and that big, high-pressure spray applications produce a fine mist that can suspend bacteria in the air and shuttle them between plants. According to his observations, that kind of spray pattern means a protective tank mix could, under certain conditions, actually increase the odds of longer-distance movement of the pathogen. The Tampa Free Press reported Vallad’s warnings to growers.
Testing New Sprayer Tools
UF researchers say they are now testing alternative nozzle types, low-volume air-assisted sprayers and changes in sprayer setup to cut down on bioaerosol production while still getting protectants into the canopy where they are needed. Those options, along with the preliminary air-sampling results, were shared with attendees at UF’s Tomato Field Day hosted by the Gulf Coast Research and Education Center. The UF IFAS Gulf Coast Research & Education Center posted highlights from the event.
What Growers Can Do Now
For now, UF specialists urge growers to stick with basic disease-prevention tactics. As detailed in UF/IFAS, that starts with using disease-free transplants, avoiding handling wet foliage and timing spray applications for drier windows instead of waiting until disease pressure is severe. For field-specific strategies and equipment questions, growers are encouraged to contact their local UF/IFAS Extension office while researchers work through follow-up trials.
Next Steps
Researchers say they need more air sampling under different weather patterns and disease levels to map how far aerosols can travel and to pinpoint when spray applications are most likely to increase risk. The UF team is continuing field trials and updating growers as they refine their recommendations. The UF IFAS Gulf Coast Research & Education Center has shared ongoing work and Tomato Field Day photos as the research moves forward.
