Anthracnose Disease of Deciduous Shade Trees

Published: May 18, 2021

Figure 1 Leaf spots with irregular shape on maple leaves. Photo: Peng Tian

With recent cool and wet weather, we have observed the presence of anthracnose diseases in several shade trees. Anthracnose is a fungal disease caused by a group of pathogenic fungi that infect a very broad range of shade tree and shrubs, such as maple, elm, oak, sycamore, poplar and ash.

Symptoms of anthracnose start to show up in spring as small dark brown circular or irregular-shape spots (Figure 1). The small spots develop into large blothces along the veins and spread to the edge of the leaves (Figure 2). As the dead areas of the leaves expand, the leaves are distorted, showing blister look. This disease can spread very fast by attacking the newly developed leaves and can affect over 80% of the canopy when the environment favors these pathogens. The fungal spores are transmitted by wind or rain splash to other trees and can infect one tree repeatedly. The young leaves may die and fall from the tree due to heavy infection. As the time passes by, the diesae may stop progressing later in the season and the new leaves will again emerge. The fungal spores can survive in fruiting bodies (pycnidia) on the infected leaves, twigs or cankers on the tree during the winter.

Figure 2 Anthracnose lesions spread along the veins and leaf margins. Photo: Peng Tian

Disease management:

1. Sanitation by removal the infected leaves and branches is important for homeowners. Raking and burning the fallen plant debris can reduce the total quantity of the inoculums in that site.
2. This disease favors high humidity and cool weather, thus improvement of air circulation and prevention of water splash are helpful in reducing the transmission of this disease.
3. The trees that suffer from this disease may lose lots of leaves in that season, therefore adequate nutrient and water by good fertilization and irrigation is significant for improving plant vigor.
4. Resistant/tolerant cultivars of trees are always highly recommended
5. Chemicals are usually used for valuable trees or trees in nursery environment. Suggested preventative fungicide include one of these active ingredients: copper, chlorothalonil, captan, ferbam, mancozeb, maneb and thiram. Fungicide application should be done two or three times, at 14-day intervals, starting at budbreak and early shoot growth.

References:

1. Anthracnose disease of trees, Josephine Mgbechi-Ezeri and Caroline Jackson, Plant Diagnostic Clinic, University of Missouri (https://extension.missouri.edu/media/wysiwyg/Extensiondata/Pro/PlantDiagnosticClinic/Docs/anthracnoseDiseaseTrees.pdf)
2. Maple leaf blister and anthracnose: Two diseases of maple leaves, Lori Imboden, Michigan State University Extension
3. RPD No. 621 - Anthracnose Disease of Shade Trees, Nancy R. Pataky, University of Illinois Extension (http://ipm.illinois.edu/diseases/series600/rpd621/index.html)

For appropriate diagnosis, the MU Plant Diagnostic Clinic can help you confirm if your plant has this disease. We encourage you to visit our website (https://extension.missouri.edu/programs/plant-diagnostic-clinic) and review submission guidelines before submitting your sample. If possible, you may take photos and send them to plantclinic@missouri.edu.

We just uploaded a new webinar about sample submission guidelines on YouTube to help you submit your sample step by step.
Please click here: https://www.youtube.com/watch?v=4dUcYKKFwaI

For sample submission and fee payment, you can either:

1) Visit our new online submission system at https://extension.missouri.edu/services/plant-disease-sample. Fill out the submission form online using your computer or mobile device and make payment online securely with a credit card.

2) Download the submission form at https://extension.missouri.edu/programs/plant-diagnostic-clinic/sample-submission. Fill it out and send to us together with your sample and payment. Check or money order. No cash please.

Contact Information:

University of Missouri-Plant Diagnostic Clinic
28 Mumford Hall
Columbia, MO 65211
Phone: 573-882-3019
Email: plantclinic@missouri.edu