Microbial antagonists, i.e. bacteria or fungi that show disease-suppressing effects, can be applied. They can differ in their mode of action and in their specificity. For example, their suppressive effect can be caused by a strong growth, or they directly form active substances (metabolites) that suppress pathogens. Depending on the mode of action, intact microorganisms or their metabolites are used. Only few microbial preparations are registered as pesticides. We are working on the possible uses of microbial antagonists to substitute or supplement chemical-synthetic agents. Alternative active ingredients can originate from the field of natural substances. We are investigating new approaches for plant protection and plant strengthening agents that can be used in practice to regulate plant diseases.