It causes twig canker and dieback, leaf and shoot blight, and often substantial defoliation. The fungus that causes sycamore anthracnose, Apiognomonia veneta , overwinters in twigs on the tree and becomes active whenever temperatures permit its growth. Twig dieback occurs when a canker forms, enlarges, and girdles the twig .The buds may become infected and killed and those trees with high twig and bud mortality produce only thin crowns by late spring. Ash anthracnose is a common but seldom serious problem on white and green ash. The disease is caused by the fungus Apiognomonia errabunda .
Symptoms first appear as water-soaked spots on the expanding shoots and leaves.
Then spots enlarge and develop into brownish green to brown lesions. The lesions are often associated with leaf veins and margins. Growth of the infected tissue slows or stops as the rest of the leaf continues to expand. As a result, the leaf tissue around the lesion becomes twisted and wrinkled and defoliation also may occur. Young shoots that become infected may suddenly wilt and shrivel, especially following a rain.