Tomato leaves with small, circular spots may be infected with Septoria leaf spot disease, caused by the fungus Septoria lycopersici. Septoria leaf spot and early blight are the most common leaf diseases of tomato. The symptoms of Septoria leaf spot are small spots with dark brown margins and tan to gray centers. These spots usually occur on the lower leaves near the ground. Black specks in the center of the leaf spots are the spore-producing (reproductive) structures of the fungus. Severely spotted leaves turn yellow, die, and fall off the plant.
Purchase disease-free plants and practice crop rotation. Avoid wetting the foliage when watering the plants; wet leaves set up a favorable environment for disease development. There are several home garden fungicides available for preventing tomato leaf blights. Follow label instructions. Contact your local Extension office for fungicide recommendations.
