Postharvest diseases caused by Geotricum candidum (sour rot), Penicillium digitatum (green mould), and P. italicum (blue mould) are the most important negative factors affecting handling and marketing of citrus fruits in Egypt. A new formula containing stevia leaf powder and a mixture of the three commercial chemical active ingredients: ketoconazole, fluconazole, and itraconazole has been successfully applied. Either chitosan or water wax were used as carriers, against fruit mould pathogenic fungi under laboratory and storage conditions. Results of the in vitro test showed that a complete reduction in linear fugal growth was observed when the ingredients of the new formula were used individually at a concentration of 400 μg/ml each, while a mixture of all the tested chemicals had a superior effect with all fungal growth completely inhibited with the use of the mixture at a concentration of 100 μg/ml. Similar results were recorded on citrus fruits which were coated with the suggested formula of chitosan or wax containing chemical compounds as a semi applicable technique using navel orange peel discs. Furthermore, the obtained results were confirmed using in vivo testing on navel orange and lime fruits, under artificial inoculation conditions of the pathogenic fungi within a storage period extended for four weeks. The proposed approach provides the treated agricultural products with long acting protection against microbial invasion and even association. This formula could be used as a fungicide alternative for protecting the agricultural products which have high moisture contents. The formula can be used against mould pathogens to prolong the healthy shelf life of the agricultural products. Such a treatment is safe, cheap, easily applied, and without residues which are harmful to people and the environment.