Eight polymers capable of forming aqueous gels were compared for their capacity to retain hydration over time, to promote spore germination, and to prolong the viability of germinated spores (= germlings) of Alternaria cassiae, a bioherbicide agent for sicklepod. When compared at a standard 0.1% w/w (gel/water) concentration, the eight gels retained hydration for 6 d with no significant differences among them in the rate of dehydration. The best concentration of each gel that yielded 95 to 100% spore germination within 6 h after hydration was then chosen, and the gels were compared at these concentrations to determine the duration of effectiveness of the gels. The effectiveness was rated on the basis of the proportions of alive germlings versus germinated spores and alive germlings versus total spores, determined with the aid of a fluorescent vital stain. Based on these two parameters, the most effective gel was Kelzan® xanthan gum. However, all gels supported > 50% alive germlings over a period of 1 wk, suggesting that the addition of any of these polymers to the inoculum suspension should enable the fungal propagules to remain moist for a prolonged period, benefit from the high ambient moisture to improve germination, and promote disease development. Accordingly, seven of these gels were tested for their ability to enhance pathogenicity of a mycelial inoculum of A. eichhorniae, a bioherbicide agent for waterhyacinth. Gellan gum and Kelgin®-HV were most effective in promoting disease, followed by Evergreen® 500 polyacrylamide, and Kelgin®-LV, Metamucil®, Kelzan® xanthan gum, and N-Gel™ were no better than the control inoculum without any gel. Thus, the gels may have differential effects on different fungi and inoculum types. Nonetheless, the results confirm the utility and feasibility of hydrophilic gels as formulating materials for bioherbicides.