In late spring and early summer, anthracnose is the most common leaf disease of green ash. Following rain events, watch for falling leaves during the first half of June. These infected leaflets are being shed by the tree.
Anthracnose is a common name for several leaf diseases that are found on a large number of hardwood species but are most severe on ash, oak, and maple. Anthracnose leaf diseases are caused by a few species of fungi, which over winter on the buds, bud scales, and branches. Growth of these fungi begins early in the spring. Sufficient spores are produced for leaf infection and disease development during any period of warm, wet weather in the spring and summer. Disease severity varies greatly from year to year.
Symptoms of anthracnose on infected leaves range from tiny, dead spots to large, dead blotches. Many leaves become curled and distorted due to the infection. Severely infected and dead leaves are shed. The symptoms are more severe in the lower crown. Control is not recommended. Defoliated trees will continue to add foliage and the rate of infection will decrease as the season progresses.