Cladosporium leaf spot symptoms appeared as small round, tan leaf spots on spinach bedding plants growing in a greenhouse.
Dark green spores and mycelium eventually develop in the centers of these spots. The presence of dark green sporulation distinguishes Cladosporium leaf spot from anthracnose and Stemphylium leaf spot diseases, both of which also form circular lesions. Leaf wetness and high humidity are conditions that favor this disease.
This pathogen is seedborne. Copper sprays can be used as a protectant.
Reference: University of California IPM