Tuesday, April 16, 2013

Evidence of Anthracnose Infection

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.
For more information on the basics of anthracnose see our previous posts here and here.

Today we'll focus on symptoms on infected leaves. These symptoms 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 (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 (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.

If you are so unfortunate as to have severely infected trees, then it is quite possible that they may lose their leaves. But if defoliation occurs in spring or early summer, a tree will usually produce a second crop of leaves (see photo below).

Symptoms on most trees are confined to the leaves. On sycamores and oaks, however, the fungi may also affect twigs, buds, and shoots.

This severely infected tree is refoliating.

Symptoms: Sycamores, Oaks

On sycamores, there are four distinct stages of anthracnose: twig blight, bud blight, shoot blight, and leaf blight. These stages often overlap, as shown below; any one or more stages can be seen during the spring or summer when weather conditions are just right for the development of the disease. Above you'll see Anthracnose infection along the vein of an oak leaf.

On oaks in the white oak group, symptoms are similar to those on sycamore, but less severe.

Twig blight. Twig blight occurs in the spring before the leaves emerge. After the tips of 1-year-old twigs are killed, small, black fruiting bodies of the fungus soon break through the bark of the dead twigs (below).  Fungal fruiting bodies break through the bark of a dead sycamore twig. Later, cankers-dead areas in the bark-may appear on older branches below the dead twigs. These cankers girdle and kill the branches.

Bud blight. Bud blight occurs at the same time as twig blight. When cankers girdle the individual buds, the buds die before the bud caps begin to break.

Shoot blight. During the shoot blight stage, emerging shoots and new immature leaves suddenly die.

Leaf blight. In the leaf blight stage, both young and mature leaves are infected with spores produced on twigs and branch cankers. Necrotic spots or blotches are found on the leaves, and dark-brown fruiting bodies of the fungus are found on diseased leaf tissue.

Now that you know about the symptoms and different kinds of blight, it is important to understand how to prevent the spread of the blight. You can control the spread of blight. Stay tuned to find out more.

This was brought to you by Trees "R" Us, Inc. A full service tree care company serving the Chicago suburbs, including Chicago's North Shore, and the north and northwest suburbs of Chicago.

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