Research was conducted on the effect of foliar fertilizers containing various macro and microelements (N, Ca, K, B, Cu, Fe, Mn, Mo and Zn) on mycelial growth, spore germination and antagonism of Trichoderma isolates. It was found that foliar fertilizers cause changes in the development and antagonism of Trichoderma spp. The kind of changes depends on the fungal isolate and fertilizer composition. T. harzianum isolate, in which a decrease in spore germination index and considerable changes of mycelial growth and antagonism rate were observed, proved the most sensitive to the chosen fertilizers. Among the selected fertilizers Mikrovit Cu acted most unfavourably, since it most strongly inhibited mycelial growth and T. harzianum spore germination, and diminished the antagonism of Trichoderma isolates towards B. cinerea and R. solani. It was found that Mikrovit 1, potassium Alkalin and Wapnovit fertilizers significantly increased the growth rate of T. harzianum mycelium. Germination of T. pseudokonigii and T. viride spores were most stimulated by Mikrovit Mn, whereas Molibdenit inhibited this process in T. viride. Potassium Alkalin is a fertilizer which favourably affects the antagonism of Trichoderma isolates towards B. cinerea and R. solani. On the other hand, Mikrovit Mn and Mikrovit Cu preparations diminish biocontrol abilities in the analyzed Trichoderma isolates toward pathogens.