The Norman Transcript

Features

March 22, 2013

Oak disease is a growing problem

NORMAN — Losing a tree can be stressful for homeowners, financially and emotionally.

For all the years it takes a tree to mature, it is devastating for one to die rapidly because of disease. This is true with hypoxylon (Biscogniauxia) canker in oaks. Hypoxylon canker has been in Oklahoma a long time. However, significant reports didn’t occur until 1979 when outbreaks were documented in 14 counties.

Hypoxylon canker is a fungal infection occurring on various oak species, including blackjack, live, post, southern red and white oaks. The fungus is found in wooded areas, pastures, new construction areas and established residential areas. I’ve seen the most devastating outbreaks in the cross-timber areas of eastern Cleveland County, where acres of trees have been lost.

Hypoxylon canker is exacerbated by environmental stressors such as drought, heat, physical injury to the tree or roots and chemical drift. Thus, healthy trees are more resistant to the disease.

Like most fungi, hypoxylon canker is spread from one tree to the next by wind, rain, tools and insects. Research shows the fungus enters the tree through wounds, growing through the wounds and sapwood and causing decay. Hypoxylon canker may be dormant in seedlings and young trees that show no outward symptoms.

However, due to environmental stresses, the fungus can overcome the tree’s resistance and begin causing damage.

Symptoms of hypoxylon canker include yellow, wilted leaves followed by death of entire branches. As the disease progresses and branches die, bark is lost exposing the fungal growth or stroma. The stroma appears as sunken areas that are brown, silver, black, dark gray or white, depending on the life stage of the fungus. As the fungus matures, the stroma hardens.

The exposed lesions or cankers may be seen on upper branches before progressing to the trunk. In one year, the canker may not spread at all, up to 3 feet on a single branch, or the entire length of the tree. Death of the tree may take one or two years but may seem like weeks if early symptoms go unnoticed. There are no effective means of control for hypoxylon canker.

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