Anthracnose

Colletotrichum gloeosporioides, Discula fraxinea and other host-specific fungi (fungus)

HOST Many shade trees including ash, maple, oak, elm

DAMAGE/SYMPTOMS Anthracnose is a foliar disease caused by numerous plant pathogenic fungi. In spring, tan to brown blotches appear on new leaves along leaf veins. The blotches enlarge and often cause distortion of the leaves. Young, infected leaves may drop in late spring. Leaves on lower branches are most often affected. Cankers may develop on branches and young shoots may die back. Infection is most severe under cool, wet conditions.

DISEASE CYCLE The fungus overwinters in infected leaf debris on the ground or in cankers on branches. In spring, spores are produced on the old leaf debris and canker tissues. The spores are dispersed by wind and rain and infect newly emerging leaves. New spores are produced on the newly infected leaves, which then infect new growth as long as the temperatures stay low and sufficient moisture is available.

MANAGEMENT Anthracnose infection does not result in tree death and trees usually push out new leaves by summer. Rake up fallen leaves and prune out infected twigs and branches. Disinfect pruning tools after each cut with 70% ethyl alcohol or a standard household disinfectant spray. Chemical treatments are generally not recommended unless the disease is a continuing problem. High value trees can be protected by applying chlorothalonil- or copper-containing fungicides in early spring when buds first start to open. One to two additional sprays should be applied in 10- to 14-day intervals, strictly following instructions on the pesticide labels.

A One-sided distortion of leaves. B Brown necrotic areas on leaves. C Necrotic areas on leaves increase in size. D Shoot dieback caused by anthracnose infection.