This research project aims at developing an alternative to Cu biocides in the form of Quaternary ammonium compounds (Quat) as an antimicrobial agent. While Quat compounds are powerful antimicrobial agents they are not known to be used directly on plants because of potential toxicity to plant tissue. Fixed-Quat is a non-phytotoxic Cu-alternative antimicrobial formulation in which Quat is combined with other inactive ingredients (such as silica gel and silica particles). In the previous reporting period, a new nanoformulation, Fixed-Quat E nanogel was synthesized with a quat concentration of 13,500 ppm (�For Food Use� Quat used). In this reporting period, Fixed-Quat A II and Fixed-Quat E were further optimized to a quat concentration of 20,000 ppm (�For Food Use� Quat used). FTIR was used to confirm silica and Quat interaction of the concentrated formulation and peak shifts similar to previous batches were observed. The Fixed-Quat A-II and E nanogel�s safety was tested by phytotoxicity studies carried out in a Panasonic Environmental Test Chamber (Model MLR- 352H) which allowed for controlled day/night cycling temperatures, light intensity and humidity to simulate summer weather conditions (biocide application season). Studies conducted on Sour orange, a common citrus variety and Roma Tomato sp, an ornamental plant revealed no sign of plant injury when tested with Quat concentration as high as 1000 ppm. It is noted that EPA maximum concentration for Quat industrial use (as surfactant/flocculating agent) is 200 ppm, indicating a large therapeutic window. Antimicrobial studies of optimized Fixed-Quat E nanogel was conducted against several model bacterial species, Xanthomonas alfalfae subsp. citrumelonis (Citrus Canker Surrogate), Pseudomonas syringae pv syringae, a gram negative causative agent of bacterial speck in citrus and tomato sp and Clavibacter michiganensis subsp michiganensis, a gram positive causative agent of canker and systemic infections in tomato. Studies were conducted to determine the Minimum Inhibitory Concentration (MIC) and compared against Kocide 3000 and copper sulfate. MICs of Fixed-Quat A-II and E 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. MIC results indicate no loss in efficacy when combined with different silica sources, thus displaying strong potential for commercial usage. Optimized versions of Fixed-Quat A-II and Fixed-Quat E are currently undergoing Citrus Canker trials on Ruby Ray grapefruit in Vero Beach, Florida.