Fusarium avenaceum, F. oxysporum, Alternaria alternata, Botrytis cinerea, Rhizoctonia solani, Mucor sp., Aspergillus niger, Penicillium spp. were the most often isolated species from fiber seeds. The antagonistic action of Trichoderma lignorum T 13–82 in relation to seed contaminants was evaluated. The use of Trichodermin-BL, based on that antagonist, applied as pre-sowing seed treatment and on growing plants decrease diseases incidence. The application of Trichodermin-BL improved a set of biometrical and physiological parameters during crop vegetation, increased the yield and raised flax fiber quality.