When Fungus Attacks

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Yellow veins on leaves can be a sign of oak wilt

Credit: William M. Ciesla, Forest Health Management International, Bugwood.org

Oak wilt is caused by the fungus Ceratocystis fagacearum. No one knows where it came from, but experts think it's a non-native disease.

What Does It Do to my Trees?

The fungus can be spread by beetles, by firewood, or through roots of neighboring trees. Infected trees produce gummy material that plugs up their water vessels.

Here are some signs that oak wilt has hit your woods:

• Wilting. Trees with oak wilt start to wilt from the top down. A few branches wilt at a time.
• Falling leaves. On red oaks, leaves fall off quickly during the spring and summer—and without other influences, such as insect attack or drought. When they fall, they may be green, brown, or a combination of both.
• Vein banding. On the kind of oak known as a live oak, leaf veins often turn yellow, then brown.
• Fungal mats. Look for narrow cracks in the bark of red oaks. If you remove the bark, you can see a fungal mat that often smells like rotting fruit.
• Spread. The infection spreads through roots and spores to neighboring trees, creating a ring with dead trees in the middle and wilting trees surrounding them.

If you think your trees have oak wilt, there are steps you can take to save other trees on your property.