Spots can also form on petioles, stems, and fruit. Fruit is usually infected at the calyx end, and the lesions can get quite large spreading down the shoulders of the fruit. Lesions on the fruit are usually dark brown to black in color and usually contain the concentric ring pattern. High levels of disease can lead to significant defoliation, which exposes the fruit and results in sunscald. Septoria leaf spot also first appears as small spots on the older leaves.
Spots are usually tan to gray in color with a dark brown margin.
Small black specks, which are the fruiting bodies of the fungal pathogen, develop in the center of the spots. The fungal pathogens that cause Septoria leaf spot and early blight overwinter primarily in infected crop debris in the field. Both can also come in on infected seed, although this is usually not a problem on commercially produced seed. Other than a three to four year crop rotation schedule and the use of early blight resistant cultivars, the only effective means for controlling these two foliar diseases is the regular application of fungicides. Applications should begin when the plants start to flower, or at the first sign of disease in the planting.