Some diseases are beginning to show up. And, in Mass they report bacterial canker. All three diseases start out affecting leaves, but early blight can infect fruit and bacterial canker can invade the vascular system. Early blight is characterized by dark brown bull s eye-like lesions on lower leaves. Later it will appear as rotting at the stem end of the tomato fruit.
Early blight is carried from season to season on crop debris.
Crop rotation is important and remember that if you put diseased plants into your compost pile it better get hot or do not use that compost on your tomatoes next year. Mulch helps because the initial infection is by splashing spores out of the soil. If the infection is early, picking of diseased lower leaves helps. Copper sprays will keep the disease from spreading if you keep the plants tissued covered. Leaf mold causes pale yellow spots on the upper surface of leaves and a corresponding felt-like olive green growth on the underside of the leaf.