By Flavia Tabay Zambon and Paulo Eduardo Branco Paiva
Florida’s citrus industry has faced severe decline due to huanglongbing (HLB, also known as citrus greening). Production has dropped 92% since the 2003–04 season, according to the U.S. Department of Agriculture Economic Research Service.
Growers have relied on cultural practices, tolerant varieties and antimicrobial treatments, especially oxytetracycline (OTC), which has recently shown compounding benefits in yield and fruit quality. However, no sprayable compound has yet proven effective for HLB suppression in citrus, despite success in other crops such as apples and peaches. The ongoing “Grove First” project continues to evaluate new chemistries, but large-scale results are still pending.
Bio Extra Verde (BEV), a Brazilian biofertilizer, has shown promising field responses in fruit set, flowering, yield and quality. Its active components — eugenol (from clove) and ricinoleic acid (from castor bean oil) — have documented antimicrobial and insect‑repellent properties, though they have not been tested previously in HLB‑affected citrus.
This report summarizes preliminary results from BEV applications in the Millennium Block research site at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Indian River Research and Education Center (IRREC) and in two commercial groves.
The Millennium Block was planted in 2019–2020 and harvested for the fourth time in 2025. BEV applications began in March 2025 following the manufacturer’s protocol: 1:1000 dilution, sprayed every 15 days for 90 days, then monthly. Commercial blocks began treatments in June 2025 under the same protocol. Data collected included fruit weight, yield (boxes/acre), fruit drop, fruit size, total soluble solids (TSS), titratable acidity (TA) and TSS:TA ratio.
MILLENNIUM BLOCK RESULTS
UF‑914 Pummelo Hybrid
UF‑914 grafted onto US‑942 showed no statistically significant response to BEV for any measured variable (good fruit weight, bad fruit weight, yield, TSS, TA or ratio). P‑values ranged from 0.084 to 0.94, indicating no treatment effect at the 95% confidence level. Although numerical increases were observed in some variables, variability prevented statistical significance.
Ray Ruby Grapefruit
Ray Ruby grafted onto two rootstocks (US‑942 and 2247×6070‑02‑2) also showed no significant treatment effects. The only significant difference detected was an effect on TSS, with 2247×6070‑02‑2 rootstock producing higher soluble solids (8.12 vs. 7.38). This aligns with prior evaluations of this new rootstock.
COMMERCIAL GROVE TRIALS
Because research‑station conditions do not fully reflect commercial management, BEV was also tested in two grower‑managed blocks: a grapefruit block and a sweet orange block for the fresh market.
Red Grapefruit UF N40‑11‑7
This block included trees grafted onto C‑54, UFR‑5 and US‑942 rootstocks. BEV was applied from May to December 2025. Fruit drop and quality were evaluated in February 2026.
Fruit drop was significantly reduced across all rootstocks, with 22.2% drop in control trees and 14.8% in sprayed trees. Rootstock also influenced the reduction in fruit drop regardless of the treatment:
- C‑54: 9.38%
- US‑942: 17.1%
- UFR‑5: 29%
Fruit size showed a significant treatment × rootstock interaction (Figures 1 and 2). BEV increased fruit size only in trees grafted onto US‑942, while C‑54 and UFR‑5 showed no meaningful response. This suggests that BEV’s physiological effects may depend on rootstock vigor or nutrient dynamics.
Juice Brix was influenced by rootstock but not by BEV. The highest Brix was on US-942 and C-54. The lowest Brix was on trees grafted onto UFR-5. No treatment or rootstock effects were detected for the juice ratio.
OLL‑8 Sweet Orange
OLL‑8 grafted onto rough lemon was treated from May to December 2025 and harvested in April 2026. Due to harvest losses, only four replicates per treatment remained.
BEV significantly increased Brix, from 7.85 in control trees to 9.43 in sprayed canopies. This increase resulted in a significantly higher TSS:TA ratio, with thecontrol at 12.0 vs. and the sprayed canopies at 15.1. No significant effects were observed for fruit size or fruit drop.
PRELIMINARY CONCLUSIONS
Early results indicate that BEV may offer benefits in commercial citrus production, particularly in reducing fruit drop in grapefruit and improving juice quality in OLL‑8 sweet orange. Responses appear to be rootstock‑dependent, with US‑942 showing the most promising interactions.
Because OTC provides only temporary suppression of HLB bacteria, growers are seeking complementary tools that support tree health and productivity. If future research confirms these trends, a combined OTC + BEV strategy could be a valuable addition to HLB management programs. Continued multiyear evaluation is essential to determine long‑term effects, optimal application timing as well as interactions with rootstock, nutrition and disease pressure.
Acknowledgments: The authors appreciate ImunoAgro for donating the product and the UF/IFAS vice president of research for providing funding for this project.
Flavia Tabay Zambon (f.zambon@ufl.edu) is an assistant professor at the UF/IFAS IRREC in Fort Pierce. Paulo Eduardo Branco Paiva (paulopaiva@iftm.edu.br) is a professor at the Federal Institute of Education, Science and Technology in Brazil.
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