Early blight is a fungus disease which shows up as a leaf blight on the lower part of plants.
As the disease progresses, leaves turn yellow, wither, and drop from plants. Tomato plant severely infected by early blight produce low yields of undersized fruit. Generally, fruit are also show signs of sun-scald since leaves aren't present to protect fruit from direct sunlight. Early blight tends to get off to an early start in the spring when wet weather is experienced soon after transplants are set. These type conditions are ideal for infection of young tomato plants by the early blight fungus.