Oak Anthracnose

Anthracnose infects a large number of trees–but mainly oak, maple, sycamore and ash. Oak anthracnose is caused by the fungus Apiognomonia quercinia–Discula quercinia. It is a leaf-blight disease that usually does not cause serious damage to the tree but can result in defoliation in severe cases. Once an oak tree has suffered from anthracnose, ensure that the tree does not get infected again the following year, as the spores may survive in some infected parts of the tree.

Leaf Symptoms

Young leaves that appear during the spring season are most susceptible to oak anthracnose disease. Symptoms of oak anthracnose infection are manifested in the form of brown margins because the fungus kills the tissue in this region. Heavily infected leaves become curled and deformed. Additional brown necrotic spots are formed on the leaf blade that coalesce to grow bigger with time. These spots are usually in and around the leaf veins. Oak anthracnose disease most commonly affects foliage in lower branches where there is high humidity. From here it moves up to infect the other leaves.

Twig Symptoms

Oak anthracnose disease may also appear on twigs in the form of twig cankers. In severe cases, twigs may die before they can bear buds in the next spring causing what is known as branch dieback in which the branches start to die starting from the tip. Lower branches are also affected with shoot blight.

Spread

Spores of the fungus may survive through the winter on infected parts of a tree that are scattered by rainfall in the next spring season onto new leaves and shoots. If the temperatures are low enough, the spores germinate and infect new plant growth. According to Paula Flynn, plant disease diagnostician with the Iowa State University, infection is most severe at low temperatures. Increasing temperatures during midsummer help stop the spread of infection.

Weather

The anthracnose fungus becomes most potent in cool temperatures and wet conditions. Water on leaves promotes fungi spores to germinate. If wet conditions prevail, oak anthracnose infections repeat and spread onto newer parts of the plant.

Control and Treatment

If a tree has suffered from oak anthracnose disease, ensure that more infections do not occur in the ensuing spring season. Remove all the leaves around the tree. Add fertilizer to help the tree make up for lost food due to infection. Pruning branches also reduces probability of new infection. Do not prune during April, May or June.

Call 573-789-2556, or email us today for a free consultation on your specific questions about tree diseases.