By Lauren Fessler Mathews, Ana Redondo and Ozgur Batuman
Citrus canker continues to impact Florida citrus, increasing premature fruit drop and decreasing yield and fruit quality. While copper sprays have long been relied upon to control this disease, concerns about environmental impact and possible resistance development have led to efforts to find sustainable alternatives.
Previous studies have shown that plant defense inducers alone may have the potential for citrus canker control, but University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers wanted to see if they could also be used in rotation with traditional copper sprays at a reduced frequency to effectively manage citrus canker in the grove.
A field trial was conducted on mature Hamlin trees at two commercial sites in Collier and Charlotte counties with known canker pressure. Application of Kocide 2000 at a 21-day interval was used as the standard for canker control. This was compared to reduced frequency of Kocide 2000 and the use of plant defense inducers (Actigard and a proprietary product abbreviated PDI 7), both alone and in rotation with 42-day intervals of Kocide 2000.
In the commercial plot in Collier County, Actigard alone as a spray, and in rotation with Kocide 2000 at 42-day intervals as both a spray and a drench, reduced the incidence of fruit lesions to the same level as the standard 21-day intervals of Kocide 2000. In the Charlotte County plot, all treatments except Actigard drench reduced fruit lesion incidence to levels comparable to the standard 21-day interval of Kocide 2000 (Figure 1).
The treatments also significantly reduced the incidence of leaf lesions, but this effect was not consistently observed across plots. Therefore, the trials need to be repeated to better understand their potential to reduce leaf lesions.
These preliminary results indicate that using plant defense inducers, particularly in combination with less frequent copper applications, could be a viable way to reduce copper use while maintaining adequate citrus canker control. Future trials will aim to confirm these results and investigate how the use of plant defense inducers in combination with oxytetracycline injections could influence fruit drop and benefit yield and fruit quality.
Acknowledgment: This project has been supported by funds from the Citrus Research and Development Foundation since 2025.
Lauren Fessler Mathews is a graduate research assistant, Ana Redondo is a research coordinator, and Ozgur Batuman (obatuman@ufl.edu) is an associate professor — all at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.
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