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Oak Wilt FAQ
Oak Wilt in Central Texas: Basic Information

What is Oak Wilt?

Oak Wilt is a disease of Oak species caused by the fungus Ceratocystis fagacearum.

What trees are affected?
Any Oak species can contract or succumb to Oak Wilt. Certain species in the White Oak group seem to be more resistant to it, or at least less severely affected. Bur Oak, Post Oak, Monterey and Chinquapin Oaks are in the White Oak group.

How does Oak Wilt spread?
In Central Texas, the disease is primarily
(95+ percent) spread by interconnected root systems. For example, Oaks frequently grow in groups or motts with root systems sharing the same soils or even grafting together. Once established, the pathogen potentially has access to all trees in the group.

In the remainder of cases, new infections occur at a distance from any known disease center. These are attributed to transmission by sap-feeding beetles that have been in contact with a fungal mat, which is the reproductive stage of a fungus. In Central Texas, this is only known to occur in Spanish, Shumard and Blackjack Oaks, and even then it is uncommon.

Please be aware that a professional arborist can safely prune trees every month of the year.
There are no studies that establish a link between proper pruning wounds and the spread of Oak Wilt.

Is there a cure for Oak Wilt?
No known cure has been proven for the disease of Oak Wilt. At best, it can be managed in individual or groups of trees. A common treatment is done by fungicidal injection, which is only a management tool to suppress disease symptoms. Fungicidal injections are costly and provide no guarantees. Trees must be treated early in the disease process and re-treated on a two to four year cycle. Trees of significant importance in your landscape or community or historical trees are candidates for the effort and expense of this management practice.

Best Practices

When is it “safe” to work on my Oak trees?
When Oak Wilt exists in the immediate area (such as within several hundred feet of an existing tree), the Texas Forest Service and most local municipalities either suggest or mandate certain times of the year for pruning. However, there are many factors this approach does not consider:

(1) Pruning and construction by electric utilities is done year-round.
(2) By promoting the coldest or hottest seasons for pruning, it doesn’t account for our mild winters when insect activity can last well beyond normal limits.
(3) Almost all of the Oaks in an area of active infection will potentially be exposed to the disease. Since about fifty percent of our tree cover is Oak species, the volume of pruning work needed cannot be done in a limited two or three month period.

Are wood chips or pieces of firewood from dying or dead Oak trees a source of spreading new disease?
Live Oak wood chips, once they are composted or dried, won’t harbor Oak Wilt fungus. Firewood from dying or dead Live Oaks is not known to be a source of new disease. It is recommended that you keep the wood on your site and cover it with clear plastic. All debris from knowingly infected Spanish and Blackjack Oaks should be burned or buried in a landfill. Remember that the stump and diseased root tissue are still in the ground!

What else can I do?
Plant new trees of varying species. This is the best way to maintain and ensure a healthy urban forest. Hire a professional arborist who will make proper pruning wounds to help the tree use its own defenses to protect it from disease. Make sure the tree company sanitizes its equipment before starting on pruning work using Lysol or a bleach solution and verify that they use a light coat of pruning sealer—only on Oak trees—to provide a temporary barrier to sap-feeding insects.

Many people evaluate whether or not to treat infected trees with fungicide. Often, the money and effort is better spent on removing the dying or dead trees and planting new trees of varying species.
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