T34 BIOCONTROL is a fungicide with living microorganisms to treat sclerotinia in field crops of lettuce and leafy vegetables, pythium in greenhouses crops of tomato, pepper, eggplant, zucchini, pumpkin, cucumber, melon and watermelon and fusarium wilt in carnation greenhouse crops. It consists of strains of the fungus Trichoderma asperellum strain T34, which antagonize soil-borne phytopathogenic fungi, protecting the crops. After application of the preparation, the fungus Trichoderma asperellum strain T34, creates colonies in the soil and in the plant rhizosphere, which antagonize pathogens in nutrients and space. It also acts by parasitizing the sclerotia and activates the resistance of the plant. The application of T34 BIOCONTROL is preventative, before the colonization of phytopathogenic fungi in the plant rhizosphere.