Especially important are the periods of leaf wetness which allow spores time to germinate and penetrate the leaf cuticle. F are optimal along with 18 hours of high relative humidity. Young plants and old plants are more susceptible than are mid-season plants. Plants which have been weakened by poor nutrition, adverse growing conditions, other diseases, or heavy fruit set are also more susceptible. Another name for this disease is target leaf spot which refers to the appearance of the lesions on the upper surface of the leaves.
Lesions tend to appear first on the older leaves as small circular spots.
The spots are light brown with a light center and form concentric dark rings as they enlarge, thus the name target spot. Lesions which form on the lower leaf surface tend to be more diffuse. Fruit infections begin as sunken brown spots and may later develop a dark powdery appearance as the fungus sporulates. The infection may also begin at the blossom end with the entire fruit eventually turning brown and shriveling. The fungus survives the winter in infected crop debris as mycelium and may also survive on seed.