Walnut plantations suffer from the impact caused by a number of pathogenic mycotic microorganisms. The most common pathogen fungus is Alternaria alternata and Fusarium poae. In the framework of the research, we aimed to determine the antagonistic activity of the strain Trichoderma harzianum CNMN - FD - 16 against the identified pathogens. Thus, on the 10th day the inhibition of the pathogen A. alternata by T. harzianum is 74%. On the same day, the inhibition of F. poae by T. harzianum is 73%. Trichoderma harzianum suppressed the colonies of A. alternata of 83% - this means 4 points, and the suppression of the colonies of F. poae was 69% - registering 3 points.