Under favorable conditions for disease development, these diseases can cause extensive defoliation, resulting in sunscalding of fruit and reduction in the numbers of fruit produced. Early blight and Septoria leaf spot are fairly easy to distinguish from one another in the field. Early blight results in the formation of irregular, brown leaf lesions or spots that range in size up to 2 inch in diameter. The most important diagnostic feature of early blight is the formation of dark, concentric rings within the lesion, giving the spots a target-like appearance. Often, several lesions coalesce, causing the leaf to turn yellow, dry up, and fall off the plant.
Defoliation weakens the plant and exposes the fruit to sunscald injury.
Although early blight primarily is a foliage disease, lesions may develop on both stems and fruit. Fruit lesions are tan to brown, leathery and typically originate at the stem end of the fruit. Symptoms of Septoria leaf spot first appear as small, water-soaked spots on the lower leaves. The leaf spots generally are smaller and more numerous than those resulting from early blight. Eventually the center portion of the Septoria lesion turns light tan or gray, while the margin remains dark.