The successful rearing of predators and parasitoids is crucial for the effectiveness of biological control programs. A notable challenge in rearing phytoseiid mites, specifically Amblyseius swirskii and Transeius wainsteini, is preventing mold contamination in their diets. This study evaluated the efficacy of three herbal powders, thyme, green tea, and lemongrass, as well as the chemical agent, calcium propionate, in suppressing mold development.  Experiments were conducted using a diet composed of cattail pollen and rice husks under controlled laboratory conditions (25 ± 1 °C, 65 ± 5% RH, and 16L: 8D h photoperiod). A diet without any additive agents served as the control. To quantify mold growth within each rearing unit, a numerical index, the Mold Contamination Index (MCI), ranging from 0 to 4 was employed. The results demonstrated that calcium propionate was significantly more effective than the other treatments, achieving complete inhibition of mold development (MCI = 0), compared to the control treatment (MCI = 1.45 and 1.40 for A. swirskii and T. wainsteini, respectively). The incorporation of calcium propionate into the diet significantly enhanced population growth rates, reaching 31.95% for A. swirskii and 23.57% for T. wainsteini, compared to the control treatments, which showed increases of only 2.3% and 1.74%, respectively, over one month. In contrast, the addition of botanical powders did not inhibit mold growth and was associated with a decrease in population growth rates relative to the controls. The mixture of cattail pollen, rice husks, and calcium propionate provided sufficient nutritional support, facilitating population growth of both mite species. Consequently, the populations expanded to a total of 494.3 and 368.6 individuals across all developmental stages, originating from an initial density of 15 adult mites, within one month for A. swirskii and T. wainsteini, respectively. This study presents a promising strategy for managing mold in phytoseiid mite diets, ultimately fostering healthier rearing conditions.