The greatest impact of anthracnose is in the urban environment. Reduction of property values result from the decline or death of shade trees.
Anthracnose diseases of hardwood trees are widespread throughout the Eastern United States. The most common symptom of these diseases is dead areas or blotches on the leaves. Because of the brown and black, scorched appearance of the leaves, the diseases are sometimes called leaf blight.
The symptoms vary somewhat, depending on the host. Under certain conditions, the whole leaf dies and falls prematurely. On some tree species, the diseases may also damage twigs, shoots, buds, and fruits. Repeated defoliation reduces growth, weakens the tree, and increases its susceptibility to attack by other pests and to winter injury.
These diseases are caused by several closely related fungi, plants that reproduce by means of spores - the fungal equivalent of seeds. Spores spread the disease when moved by wind, rain, or mechanical means from one host to another.
Anthracnose fungi attack numerous hardwood species, including ash, basswood, birch, catalpa, elm, hickory, horsechestnut, London planetree, maple, oak, sycamore, tuliptree, and walnut.
Although anthracnose diseases have been found wherever these trees grow, not all hardwoods are equally affected. The diseases are particularly severe on American sycamore, white oak and other oaks in the white oak group, and black walnut. Sometimes, these species are almost completely defoliated; and on black walnut, nut production is affected. Infections are frequently found on other oak species, including scarlet, black, red, and southern red oaks; but the red oaks appear to be less susceptible than the white oaks. Pin oak, swamp chestnut oak, bur oak, and London planetree are only occasionally infected by the fungi.
Symptoms on infected leaves range from tiny dead spots to large circular or irregular dead blotches, depending on the tree species. Dead areas are black, brown, or purple. On sycamore and maple (see picture below), infected areas are often found along the veins and midrib of the leaf. The dead areas may merge until the whole leaf dies.
Infection in the early spring may turn the leaves black so that they resemble leaves damaged by frost (see picture below). If they are not killed by the fungi, young leaves may become distorted by the unequal growth in healthy and infected parts. Distorted leaves are common on oaks.
~ Anthracnose on Norway maple. ~ Healthy and anthracnose-damaged leaves on sycamore.
When severely infected, trees may lose their leaves. But if defoliation occurs in spring or early summer, a tree will usually produce a second crop of leaves (see picture below).
Symptoms on most trees are confined to the leaves. On sycamores and oaks, however, the fungi may also affect twigs, buds, and shoots.
Severely infected tree is refoliating.
Symptoms for Sycamores and Oaks
Anthracnose infection along the vein of an oak leaf.
Twig, bud, shoot, and leaf blight on sycamore.
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