Septoria Leaf Spot appears initially as small, water-soaked spots on the lower leaves. The centers of the spots turn light tan or gray while the margins remain dark. Dark-colored fungal fruiting structures form in the spots which are typically smaller and more numerous than early blight spots.
Early Blight symptoms appear as irregular, brown lesions or spots on the leaves up to ½-inch in diameter. The dark, concentric rings in the lesions give the spots a target-like appearance. This is a distinguishing symptom to identify the disease. Several lesions can merge together and cause the leaf to yellow, dry up and drop prematurely. Leaf drop reduces the plant’s ability to photosynthesize thus reducing the energy and vigor of the plant. It can also expose fruit to an increased risk of sunscald. Early blight lesions can develop on the stem and fruit as well.
In Kansas, Septoria leafspot tends to be more common than early blight. Both fungi overwinter in plant debris, on seeds or weeds. Spores can splash or blow onto tomato plants. Warm, humid weather and heavy rainfall favor development of Septoria leafspot and early blight.
Read more at our KSRE Publication: Early Blight and Septoria Leaf Spot
