The root tips of sunflower plants are invaded and, eventually, all parts of the plant become affected. When the plant dies, the fungus produces the black fungal bodies that return to the soil with the plant debris. The fungus is able to survive in the soil for several years. The symptoms may appear early in the season but are most common near the time of flowering. Diseased plants usually occur in groups of a few to many plants.
Symptoms develop first on the lower leaves and gradually appear on leaves farther up the stem.
The leaf tissue between the veins yellows and becomes necrotic, while the areas near the veins remain green. This produces a mottling effect. Severely-diseased plants die early, before seed development. They exhibit brown, withered leaves and black streaks at the base of the stem. Masses of tiny, black, fruiting bodies are produced inside the stalk.