Introduction Early blight of tomato, caused by the fungus Alternaria solani , is perhaps the most common foliar disease of tomatoes in the Northeast and is also common on potatoes. This disease causes direct losses by the infection of fruits and indirect losses by reducing plant vigor. Fruit from defoliated plants are also subject to sunscald. Another 3 to 12 hours are required for the fungus to penetrate the plant depending on temperature.
Infections are most prevalent on poorly nourished or otherwise stressed plants.
Symptoms Early blight produces a wide range of symptoms at all stages of plant growth. It can cause damping-off, collar rot, stem cankers, leaf blight, and fruit rot. Within these lesions dark, concentric circles can be seen. The leaf blight phase usually begins on the lower, older leaves and progresses up the plant. Infected leaves eventually wither, die, and fall from the plant.