One of the most common and most dangerous diseases in rose cultivation under cover and in the open field is powdery mildew caused by Podosphaera pannosa. Powdery mildew is also a common disease in many agricultural and horticultural plant species, contributing to significant reduction in yield and/or decorative value. In the study, preparations containing amino acids or a probiotic were used to spray plants 4 times every 7 days individually or in a mixture at various concentrations to reduce the development of powdery mildew on rose plants grown under cover. Agro-Sorb Folium at the concentrations of 0.25, 0.5, 1 and 2% was shown to have an efficacy of 77.4 to 92%, depending on the concentration. Agro-Sorb L-Amino + used in the same concentrations showed an efficacy of 73 to 91%. By comparison, Agro-Sorb Folium used at 1% in a mixture with the EmFarma Plus probiotic at 0.8 and 2% had, depending on the concentration, an efficacy of 90.5 to 100% (no symptoms of powdery mildew). Agro-Sorb L-Amino + used at 1% in a mixture with the EmFarma Plus probiotic at 0.8 and 2% showed, depending on the concentration, an efficacy of 92 to 97.8%. The study showed a significant increase in the effectiveness of the EmFarma Plus preparation containing probiotic bacteria when it was combined with a 1% dose of the growth stimulant Agro-Sorb Folium or Agro-Sorb L-Amino + , compared to the use of the probiotic preparation alone. In each observation, the increase in the concentration of the tested amino acids and probiotic, used individually as well as in a mixture, was associated with a significant increase in their effectiveness. After completion of the experiment, it was found that the rose plants sprayed with Agro-Sorb Folium at a concentration of 0.5% or higher, and with NaturalCrop SL at a concentration of 1.0% had a significantly higher fresh weight of the aboveground parts, ranging from 12.2 to 18.3%, compared to the control plants.