Moniliosis (caused by Monilini spp.) is a major threat to sour cherry (Prunus cerasus L.) production, causing substantial yield losses in Russia and worldwide. Chemical control has traditionally held a leading position in plant protection systems; however, its use is associated with the development of resistant pathogen populations, pesticide residue accumulation, and adverse environmental impacts. Other conventional approaches are often insufficiently effective, labor-intensive (e.g., agrochemical practices), or restricted in application (e.g., resistant cultivars, physical methods). These limitations necessitate the development of alternative solutions, such as biological control agents. Field trials were conducted during the 2024–2025 growing seasons in orchards of the 'Mobodechnaya' sour cherry cultivar at the I.V. Michurin Federal Research Center (Tambov Region, Russia). The results demonstrated that the application of biopreparations significantly reduced the development of blossom blight and fruit rot compared to both the untreated control and a conventional chemical protection system. Biological efficacy against blossom blight reached 76.5% for the BZR483 treatment and 70.6% for BZR924, while efficacy against fruit rot was 46.7% and 50.7%, respectively. Under the challenging weather conditions of the 2024–2025 growing seasons, the use of these biological control agents also promoted a marked increase in sour cherry yield. The highest yields (1.2 kg/tree in 2024 and 2.3 kg/tree in 2025) were recorded for the BZR924 treatment.