Septoria leaf spot of Tomato
Small, water-soaked circular spots 1 /16 to 1 /8 in. (1 .6 to 3.2 mm) in diameter first appear on the undersides of older leaves. The centers of the spots are gray or tan and spots have a dark brown margin. As the spots mature, they enlarge to about 1 /4 in. in diameter (6.4 mm) and may coalesce. In the center of the spots are many dark brown, pimple-like structures called pycnidia-fruiting bodies of the fungus. The structures are large enough to be seen with the unaided eye or with the aid of a hand lens. Pycinidia are absent from early blight lesions and from lesions produced by the gray leaf fungus, Stemphylium solani, which is common in areas with consistent warm and humid conditions. Septoria leaf spot also lacks the target-like lesions so typical for Altemaria blight. Spots may also appear on stems, calyxes, and blossoms, but rarely on fruit. Heavily infected leaves will turn yellow, dry up, and drop off. This defoliation will result in sunscalding of the fruit.