Production of maiden (one year old) trees of sour cherry cultivars 'Debreceni Bötermö' and 'Sabina' under organic management where various bioproducts were used to stimulate plant growth, leaf-fall dynamics of the leaves affected by the leaf spot disease (Brumeriella jaapi Rehm.) were studied. In the first year of running the nursery, such bioproducts as Micosat, Humus UP, Humus Active, BioFeed Amin, Bio Feed Quality, Vinassa, Florovit Eco and Florovit Pro Nature were applied to the soil, first on Prunus mahaleb L. rootstocks and later on maiden trees. Another product - Tytanit and Micosat F MS 200, was used for foliar applications. The control combinations consisted of plots that were not treated at all or were fertilized with NPK, and fertilized with granular manure. The first symptoms of the disease, in the form of yellowing leaves, appeared in the sour cherry trees already in the last ten days of July. At that time there was no significant effect of the applied treatments on the degree of infection of the trees with the disease. The observations conducted in mid-August showed that the extent of infection of the maiden trees ranged from 23.8 to 47.5% depending on the type of the bioproducts used in the nursery. The least affected were the trees growing in the soil fertilized with such bioproducts as Micosat, BioFeed Amin, Vinassa and Florovit, and the most affected- those in the zero and NPK fertilization combinations. In the third period of observations, i.e. in late August, the largest number of fallen leaves in the case of 'Debreceni Bötermö' was found in the maidens in the zero fertilization combination, and the lowest- on the plots fertilized with the products BioFeed Amin and Tytanit, whereas in the case of 'Sabina' the smallest number of fallen leaves and those infected with Brumeriella jaapi was found on the plots where the products Vinassa and granulated Florovit Eco had been used to fertilize the plants.