Fungal disease – Alternaria alternata which causes brown spots mainly on the lower leaves of plants.
Alternaria (Altenaria alternata) is a fungal disease whose spores overwinter in the soil on remaining foliage.
Alternaria is a fungus causing leaf spots, sooty moulds, rots, and blights on many plant parts.
Remove affected leaves generously.
Control with a biofungicide based on the bacterium Streptomyces griseovirides: this colonizes the root of the plant before alternaria, among others, can settle down there.