Anthracnose and Other Common Leaf Diseases of Deciduous Shade Trees

John P. Damicone, Extension Plant Pathologist
Kenneth E. Conway, Research Plant Pathologist
James E. Motes, Extension Horticulturist

Homeowners are justifiably concerned when foliage of their yard trees becomes diseased and especially so when these diseases cause defoliation, twig and limb death and perhaps dying of a tree that has been defoliated several years in a row. Concerned homeowners need information on how to prevent or otherwise control leaf diseases. This fact sheet was produced to help fill this need.

This fact sheet describes the symptoms and control of leaf diseases of common deciduous hardwood trees commonly planted in yards. Diseases of coniferous trees (junipers, cedars, pines, etc.) are covered in OSU Extension Facts F-7618, “Common Diseases of Conifers in Oklahoma.” Powdery mildew diseases of shade trees are covered in OSU Extension Facts F-7617, “Powdery Mildews of Ornamentals and Fruit, Shade and Nut Trees.” Through the pecan tree is sometimes used as a shade tree, its leaf diseases are not covered here because pecan leaf disease control is discussed in OSU Extension Facts F-7642, “Pecan Diseases: Prevention and Control.” Diseases of fruit trees are covered by several OSU Extension Facts and Current Reports.

Leaf Disease Types

Leaf diseases of deciduous hardwood trees are grouped into six categories, to simplify their identification, as follows1:

• Anthracnose—Irregular dead areas on leaf margins, between and across and/or along veins, often moving onto the shoots and small twigs; sometimes whole leaves are engulfed.
• Leaf spot—Dead spot on the leaf that is well defined from healthy tissue.
• Leaf blotch—Dead area on the leaf that often diffuses into healthy tissues.
• Shot-hole—Loss of dead areas inside of spots that result in a series of holes in the leaf.
• Leaf-blister—Leaf spot or blotch that is swollen or raised, so that the area appears blisterlike on the upper surface of the leaf.
• Powdery mildew—Superficial growth of white to gray-white fungus material on leaves and shoots.

Common Leaf Diseases of Deciduous Trees²

Ash, Green and Red (Fraxinus spp.). The common leafspot and scorch on leaves is caused by the ash anthracnose fungus, Gloeosporium aridum. Large areas of infected leaves, especially along the edges, turn brown. Premature leaf drop may occur.

Birch (Betula spp.). Anthracnose of birch leaves is caused by Gloeosporium betularum. This fungus causes brown spots with dark brown to black margins.

Maple (Acer spp.). Anthracnose, caused by the fungus Gloeosporium apocryptum, can be serious on sugar and silver maples, and on box-elder, during rainy seasons. Indefinite light brown spots appear early but they may enlarge and run together, causing death of infected leaves.

Oak (Quercus spp.). Anthracnose, caused by the fungus Gnomonia quercina, is a common disease of oaks. Rainy weather favors infection and defoliation may result. Infected areas frequently run together and cause the appearance of a leaf blotch or blight. The dead areas follow smaller veins and are bounded by larger veins.

Sweetgum (Liquidambar spp.). Anthracnose of sweetgum leaves is caused by the fungus Gloeosporium nervisequum. Infection by this fungus causes black areas on the leaves.

Sycamore and London Plane tree (Platanus spp.). Anthracnose of sycamore and London plane trees is caused by the fungus, Gnomonia platani (Figure 1). The London plane tree is more resistant to anthracnose is the most serious disease of sycamore. The first symptoms appear in early spring as the leaves begin to unfurl from the leaf buds, and at this stage the disease may be mistaken for frost damage. Infected leaves that do not drop will develop light brown dead areas, usually along the veins. The spots may enlarge to cover entire leaves and cause premature defoliation.

Walnuts and butternut (Juglans spp.). Anthracnose, sometimes called brown leafspot, is caused by the fungus Gnomonia leptostyla (Syn. Marssonia juglandis). Anthracnose is a common disease of these trees. Leaflets are infected during the summer and irregular brown spots develop. Much defoliation may result.

Leaf Spot Diseases

Ash, Green and Red (Fraxinus spp.). Several leaf spot diseases occur on ash but these are considered to be minor. The most common disease in this group is caused by Phyllosticta fraxinicola. This fungus causes large, yellowish brown lesions with small black spots developing on the lower side of infected leaves. Cylindrosporium fraxini has also been reported in Oklahoma.

Basswood, linden (Tilia americana). A leaf-blight, caused by the fungus Cercospora microsora, causes circular brown spots with dark borders. When the spots are very numerous, the entire leaf may turn brown and fall of the tree.

Catalpa (Catalpa spp.). Brown leaf spots are caused by three species of fungi (Alternaria catalpae, Cerospora catalpae and Phyllosticta catalpae).

Cottonwood, Lombardy Poplar, White Poplar (Populus spp.). Leaf spots on Populus trees are caused by a variety of fungi of which Marssonia spp. is the most common. It causes brown spots and premature defoliation. Septoria spp. have also been found (Figure 2).

Dogwood (Cornus spp.). Many species of fungi cause leaf spots on dogwood. Two species are found in Oklahoma. Septoria cornicola causes brown angular lesions and the dogwood anthracnose fungus, Elsinoë corni, causes small, reddish spots.

Elm (Ulmus spp.). There are many fungi that cause leaf spots of elm. The most common one is blackspot (caused by Gnomonia ulmea). The first symptoms of blackspot appear early in the spring as small white or yellow flecks on the upper leaf surface. The flecks enlarge and their centers turn black. If infections are heavy, leaves may drop prematurely. Usually the disease becomes prevalent in the fall about the time of normal leaf drop and little damage to the tree occurs. Another common leaf spot is anthracnose caused by Gloeosporium ulmi. Infections by this fungus results in reddish brown spots.

Hackberry (Celtis spp.). Many fungi cause leaf spots on leaves of hackberry during rainy seasons. These leaf spots are seldom serious enough to require a fungicide application.

Honey Locust (Gleditsia spp.). A leaf spot of honey locust is caused by Melasmia gleditsiae (Linospora gleditschiae). Numerous black fruiting bodies of the fungus form on the lower side of the leaves.

Kentucky Coffeetree (Gymnocladus dioica). Three fungi cause leaf spots on leaves of the Kentucky coffeetree but special control measures are rarely required.

Magnolia (Magnolia spp.). Fifteen species of fungi cause leaf spots on leaves of magnolia trees. Septoria magnoliae is found most commonly in Oklahoma. It causes brown lesions.

Maple (Acer spp.). Purple-eye leaf spot caused by Phyllosticta minima is characterized by large irregular spots with brownish centers and purple-brown margins. Black fruiting structures develop in the center of the spots. The disease is most severe on red, sugar and silver maples.

The tar spot fungus, Rhytisma acerinum, seldom infects street trees but red maples in forests are frequently infected (Figure 3).

Mulberry (Morus spp.). Leaves of mulberry trees are spotted by two fungi, Cercospora moricola and Cercosporella mori, which cause reddish-brown spots. These diseases are most severe during rainy weather.
A blight of mulberry leaves is caused by a bacterium, Pseudomonas syringae pv. mori, which at first appears as water-soaked spots. The spots later become sunken and black. The leaves become distorted and infected leaves on the twig tips wilt and die.

Oak (Quercus spp.). Leaf spots on oak leaves are caused by many fungal species. In Oklahoma, the most common one is caused by Actinopelte dryina. Leaf spot diseases rarely cause much damage as they become numerous only late in the season.

Redbud (Cercis spp.). Redbud has two fungal leaf spot disease in Oklahoma. Each is caused by a Cercospora species (C. cercidicola/Mycosphorella cercidicola/ and c. cercidis).

Sweetgum (Liquidambaar spp.). A leaf spot disease caused by the fungus Cercospora liquidambaris occurs in the southeastern states and Texas and may eventually occur in Oklahoma.

Sycamore and London Plane Tree (Platanus spp.). Brown and angular leaf spots caused by Septoria platanifolia and Cercospora planicola also occur on sycamore leaves.

Walnuts and Butternut (Juglans spp.). Brown leaf spot, caused by the fungus Gnomonia leptostyla (syn. Marssonina juglandis), is a common disease of walnuts and butternut. Leaflets are infected in the summer and develop irregular dark brown or blackish spots. Much defoliation may result.

Downy spot or yellow leaf blotch, caused by a fungus, Microstroma juglandis, causes a yellow blotching on the upper side of leaves and a matching white coating on the under side of infected leaves.

Leaf Blister

Elm (Ulmus spp.). Leaf curl is caused by Taphrina ulmi. Infection by this fungus occurs in early spring and results in small blisters which eventually causes abnormal leaf development.

Oak (Quercus spp.). During cool, wet springs almost all species of oaks can become infected by the leaf blister fungus, Taphrina caerulescens. Circular raised areas occur on the upper leaf surface, causing matching depressions on the lower surface. The raised areas are yellowish-white and the depressed areas are yellowish-brown (Figure 4).

Control

Most leaf diseases of yard trees are controlled by gathering and destroying fallen, infected leaves. Where fallen diseased leaves have not been destroyed, chemical control is the alternative approach. For suggested fungicides, consult the current OSU Extension Agents’ Handbook of Insect, Plant Disease, and Weed Control.

During very rainy springs when leaf diseases become severe, two the three chemical applications, beginning when the leaves are first unfurling from the buds and repeated with the leaves are half grown and again when the leaves are fully developed, will usually provide good control.

Trees that have been affected by leaf diseases every season should also be well fertilized and watered to maintain vigor. Do not fertilize during early fall. Fertilize only after the trees are dormant.

F-7634, Anthracnose and Other Common Leaf Diseases of Deciduous Shade Trees (pdf file)

Entomology and Plant Pathology Department
P*E*A*R*L (Publications Database)
Oklahoma Cooperative Extension Service
Division of Agricultural Sciences and Natural Resources
Oklahoma State University

This publication was originally published 6-94. This page was created 4-99.