An awareness that biological control works in nature should provide the greatest stimulus to utilize the capacity of the natural microflora to bring about disease control. There are four possible ways by which microorganisms can affect the propagules, infection, and fructification of pathogenic microorganisms, and reduce or control the development of a disease. They are hyperparasitism, antagonism by naturally occurring and foreign microorganisms, immunization or cross protection, and hypovirulence. Leaf spot diseases are equally significant in causing economic disasters. To name a few, late blight of potato (Phytophthora infestans), blast of rice (Pyricularia oryzae), Helminthosporium leaf spot of maize, and bean anthracnose (Colletotrichum lindemuthianum) are known to have affected crop yields drastically. Basidiomycetous fungi, particularly the rusts, have been frequently noted as hosts of other parasites. Since the rusts produce external fructifications as a secondary inoculum helping the disease spread, they are liable to be controlled effectively by hyperparasites than other disease such as leaf spots.