The pathogen of apple brown spot disease: the visible generation is Bivalvia and the asexual generation is Discospora. The disease cycle is to overwinter on fallen leaves with mycelium, hyphae, conidia discs or ascus discs. , forming conidia or ascospores, spread by wind and rain, and can be infected multiple times.

So, use the diseased leaves to prepare a suspension of pathogenic bacteria and spray it on the surface of the plant leaves