Evaluation of microbial-based products and an inorganic chemical for control of Monilinia spp. in plum organic production

The plum (Prunus domestica L.) is one of the most important fruit crops in Bulgaria and ranks first place among all fruit species in terms of production. Organic fruit cultivation has increased rapidly worldwide in the last two decades, including in Bulgaria. Brown rot caused by fungi Monilinia laxa, M. fructigena, and M. fructicola is one of the economically most important and challenging diseases to manage in organic stone fruit production. In a 3-year study, the effectiveness of the organic liquid fertilizer Ecosist-Arbanasi (Bacillus subtilis TS 01), commercially available biofungicide Serenade (R) ASO (Bacillus amyloliquefaciens QST 713), and inorganic chemical (calcium polysulphide) to control brown rot in organic plum production was investigated. The study was conducted in an organic orchard of the Institute of Agriculture - Kyustendil at Kyustendil region of Bulgaria with plum cultivar Stanley during 2020-2022. The agro-climatic characteristics of the region have all the objective factors for the development of Monilinia spp. Calcium polysulphide applied two times alone insufficiently reduced the incidence of brown rot (45.5% efficacy). Two soil applications of Ekosist-Arbanasi (77.5% efficacy), three foliar spraying with it (71.6% efficacy), and seven spraying applications of Serenade (R) ASO (73.2% efficacy) may be sufficient against brown rot in plums. However, none of the treatments completely controlled Monilinia spp. These results show that improved integrated control management is needed for brown rot control in organic plum production.