Novel multi-metal systemic bactericide for HLB control

Novel multi-metal systemic bactericide for HLB control

Report Date: 10/12/2021
Project: 18-020   Year: 2021
Category: Other
Author: Swadeshmukul Santra
Sponsor: Citrus Research and Development Foundation

Industry-grade multi-metal formulations containing 2 wt% metallic Cu were manufactured and supplied by our industry collaborator for further evaluation. The industry-grade Cu-Mg was compared with two different versions of lab-grade Cu-Mg, Cu-hydroxide industry standard and Cu sulfate pentahydrate at the same metallic Cu content for differences in particle size, surface charge, pH, and antimicrobial efficacy. The industry-grade formulation presented an average hydrodynamic radius of 207 nm with a broader size distribution (PDI 0.482) as compared to the lab-grade formulation which had a similar radius of 293 nm but smaller size distribution (0.174 PDI). In contrast, the surface charge of both formulations was found to be comparable, indicating that the primary particle for both formulations is stable in suspension after dilution. FTIR analysis was also conducted on the formulations to compare the interactions between particle and adjuvants. Both lab-grade and industry-grade presented almost identical spectra, which indicates that the industry-grade formulation’s components behave similar to that of the lab-grade formulation. The antimicrobial properties of both formulations were compared. The minimal inhibitory concentrations (of Cu) for both materials were the same when assessed on Xanthomonas alfalfae and Pseudomonas syringae at 32 ppm Cu and 64 ppm Cu, respectively. While Clavibacter michinganesis’ minimum inhibitory concentration for the industrial-grade formulation was one stage higher than that of the laboratory synthesized formulation. Both formulations outperformed copper sulfate and the Cu-hydroxide industry standard for all pathogens tested. A more quantitative assessment of the bactericidal potency of these materials will be performed and reported. Additionally, leaf residue of the formulations was imaged through scanning electron microscopy. From our overall assessments, it was observed that both the industry and laboratory synthesized multi-metal formulations were of similar particle size, chemical characteristic, and antimicrobial potency. Preliminary field trial of the industry-grade multi-metal formulation is underway from which efficacy and metal residue data will be reported in the near future. Additionally, we will be reporting on tissue sample characterization including sap to understand the systemic movement of the A.I. 2021 harvest data is tentatively scheduled to be collected for the week of Nov 15th.              


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