In recent years, in the orangeries of the Peter the Great Botanical Garden, the affection of representatives of the Ericaceae family, the genus rhododendron (Rhododendron (L.) oomycete Phytophthora cinnamomi, has been growing. In the study of the rhizospheric soil of sick and healthy plants, a wide distribution of Phytophthora was found. representatives of this family. The dynamics of the spread of the disease from 2012 to 2019 is presented. The population of Phytophthora cinnamomi in the soils is unevenly distributed, changing its structure (abundance, survival, seasonality, life cycle) in accordance with various micro -phytocenoses. The population structure is governed by coenotic relationships with soil microorganisms. The Phytophthora cinnamomi population is “pulsating,” with a maximum population (in May-June) and a minimum in NovemberDecember. The creation of suppressive soils and suppression factors may serve as a preliminary strategy when creating measures to protect plants of the Peter the Great Botanical Garden. The results of studies of the effects of biological products (Vitaplan, Sternifag, Gliokladin) and fertilizers (Potassium humate, Ecofus) on the pathogen are presented. To increase immunity, resistance inducers (immunocytophyte, sillplant, chitosan) were used.