Quaternary Ammonium Compounds (Quat) is a powerful antimicrobial agent. However, Quat cannot be directly applied to citrus plants as a film forming fungicide/bactericide as it exhibits severe phytotoxicity and poor rainfastness. This research uses a silica based Quat delivery system (Fixed-Quat). Fixed-Quat material is non-phytotoxic and it demonstrated good rainfastness. In the previous reporting period, a new Fixed-Quat A-II nanogel formulation was synthesized with EPA approved �For Food Use� active and inerts. Fixed-Quat A-II is an improved version of previously developed formulation. Fixed-Quat A-II nanogel demonstrated no plant safety issues while maintaining exceptional antimicrobial properties. In this reporting period, a new version of Fixed-Quat AP-II containing a secondary EPA approved active having additional antimicrobial modes of action was designed and developed. The purpose was to combat any potential antimicrobial resistance against Quat active materials. Quat concentration in Fixed-Quat AP-II nanogel formulation was at 13,500 ppm level, same as the previous version. It is expected that multiple mechanisms of killing will increase the likelihood of biocidal efficiency. Phytotoxicity studies were carried out on the optimized version of Fixed-Quat AP-II in a Panasonic Environmental Test Chamber (Model MLR- 352H). The chamber allowed for controlled day/night cycling temperatures, light intensity and humidity to simulate summer weather conditions (biocide application season). Studies conducted on Vinca sp, an ornamental plant revealed no sign of plant injury even as high as 500-1000 ppm Quat (EPA maximum concentration for Quat industrial use is 200 ppm). The composition and interactions between the components was confirmed using Fourier transform infrared spectroscopy (FTIR). The morphology of Fixed-Quat AP-II nanogel was examined using Scanning Electron Microscopy (SEM), displaying sub-micron to micron composites with irregular shapes in multiple layers. Antimicrobial studies of Fixed-Quat AP-II nanogel was conducted against several model plant pathogen surrogates, Xanthomonas alfalfae subsp. citrumelonis, Pseudomonas syringae pv syringae and Clavibacter michiganensis subsp michiganensis. Studies were conducted to determine the Minimum Inhibitory Concentration (MIC) and compared against Kocide 3000 and copper sulfate controls. MICs of Fixed-Quat A-II were found to be � 1.0 �g/mL for X. alfalfae, � 1.0 �g/mL for P. syringae and � 1.0 �g/mL for C. michiganensis. Future studies will involve additional antimicrobial studies (CFU) and rainfastness evaluation.