The need to obtaining of healthy plant material and very small range of plant protection products in organic farming forces to searching for alternative means of plant production. Evaluation of Trichoderma asperellum as a growth promoter and the control effects of T. asperellum to Septoria melissae was evaluated. Also the fungi infesting lemon balm were identified. The experiment covered various combinations depending on the farming systems (conventional and organic system) and application of T. asperellum. The microorganism was used three times with one month interval as foliar spraying only in organically growing plants. T. asperellum was applied as water solution at a concentration of 10 g·l^-1 by shoulder-carried sprayer. Control plots were treated only with water, no chemical fungicides were used. Plant development and its healthiness were assessed in respect of the effect of Trichoderma. T. asperellum was capable of stimulating the plant growth and in consequence causing an increase of dried mass of herb. There was no influence on essential oil content and proportion of leaves in the dried herb. The possibility of using of Trichoderma could be promising; especially for organic farming. Among pathogens naturally infesting of lemon balm Septoria melissae was identified most commonly.

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