Anthracnose Diseases on Trees and Shrubs

There are several similiar fungi causing these diseases. The fungi are dependent on the plant and sometimes plant part invaded. The trees most often affected in Illinois include ashes, maples oaks, sycamore and walnuts. Other trees that can get anthracnose diseases include catalpa, dogwood, hickory, hornbeam, linden, and poplar.

Symptoms

On trees other than oaks and sycamores, anthracnose fungi are mostly confined to the leaves. Small, round to irregular spots that are tan to dark brown or black can enlarge to blotches encompassing mid-ribs and veins. (Veinal necrosis is found on sycamores, oaks, and maples. Disease runs along the veins.) Leaves often become severly distorted from abnormal leaf expansion. Young leaves die and fall soon after infection. Severe early defoliation (soon after leaves emerge) usually trigers another set of leaves to emerge. Sometimes several sets of leaves are produced before weather becomes warm and dry enough to reduce infection. On sycamores, buds shoots, and one year old twigs may be infected in addition to leaves. Severe dieback of shoots and twigs may result in a witches broom effect.

Control

Follow good sanitation methods such as removal and destruction of infected plant parts. Pick up fallen leaves; prune trees and shrubs for better air circulation and remove dead and diseased wood. Use resistant varities when possible: for example, the Zordan planetree is less susceptible than the American sycamore but otherwise appears similar. Black and pin oaks are more resistant than white oaks.

Fungicides may be useful on specimen trees, but multiple applications are required to protect new growth. The cost of spraying for Anthracnose, usually can not be justified by the limited control obtained. The disease will not kill the tree.

Trees that are continuously defoliated by this disease, may need to be fertilized. Contact your local Extension office for fertilizer recommendations. Water deeply and infrequently during periods of drought to help maintain vitality.

Written by James Schuster, Extension Educator, Horticulture, and reviewed by Nancy Pataky, Extension Specialist, Plant Pathology, Department of Crop Sciences University of Illinois at Urbana-Champaign.