by Wizzie Brown, Texas AgriLife Extension Service Program Specialist
As you most likely know, oak wilt is a fungus that kills oak trees. Infections have been found in 16 oak species, but no species of oak is known to be immune. The main period of infection is in the spring.
Symptoms can be seen in red oak as early as May. Leaves turn dull green or bronze, appear water soaked and wilt. They then turn yellow or brown. Damage begins at the tips and outer edges. There is a very distinct line formed between the green and brown/ bronze. Symptoms appear throughout the crown and leaves are shed from the ends of branches. Crowns of trees with oak wilt seldom have uniform brown coloring as do trees with other issues. The disease progresses rapidly with red oaks dying within 1 year of disease onset but with some dying 1-2 months after symptoms appear.
For white oak, symptoms may be the same as for red oak and the tree may die in one year, but often white oaks die slowly. In trees that are dying more slowly, symptoms may only appear in and kill 1-2 branches per year. If the fungus is allowed to persist, then the tree will slowly decline each year leading to its eventual death. Some white oaks seem to recover from the disease, but still harbor the pathogen and may spread it to nearby oaks.
There is no known way to save a tree that is infected with oak wilt. The best thing to do is prevention techniques.
- Detect symptoms early and remove infected trees.
- Breaking root grafts between diseased and healthy trees. You may use mechanical or chemical barriers.
- Do not prune trees in the spring and summer. Fresh pruning wounds can attract beetles that carry the fungus.
- If you do need to prune, paint over all tree wounds immediately.
For pictures and in depth information on oak wilt, please see http://texasoakwilt.org/
For more information or help with identification, contact Wizzie Brown, Texas AgriLife Extension Service Program Specialist at 512.854.9600. Check out my blog at www.urban-ipm.blogspot.com