Oak Wilt - A Serious Issue

By Reeve Hobbie - Our Local Master Gardener

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Oak wilt is a vascular fungal disease affecting most oak trees caused by the fungus Ceratocystis fagacearum. Symptoms vary by oak tree species, but generally consist of leaf discoloration, wilt, defoliation, and death. In fact, most infected trees die within a year. Fungicides have been found which can suppress the disease, but to date there is no real cure for the problem.

 

Leaves of dying live oak trees often develop chlorotic (yellow) veins that eventually turn brown. Red oaks, on the other hand, may have leaves that turn pale green, brown, or simply wilt. I’m not going to offer any more descriptions of the symptoms as I’m not an authority on diagnosing the disease. The symptoms vary. If you believe you have oak wilt or some other tree malady, I suggest you ask a certified arborist to come check out your situation.

 

I can share with you that the main period of infection of oaks is in the spring when sap begins to flow, and new wood is being formed. Oak wilt can be spread through the air by insects, through the ground by roots, and by humans with the movement of infected oak wood from one location to another.

 

Spread by Beetles

Here’s what can happen. Fungal mats can form beneath the bark of an oak in the spring. These mats produce spores. The fruity odor of these fungal mats attracts many kinds of insects, the most prevalent being the sap-feeding nitidulid beetle. The fungus can be transported by these tiny beetles (smaller than ladybugs) as they emerge from mats and visit fresh wounds or cuts on healthy oaks.

 

Within 10 minutes of a cut being made on an oak, an infected beetle could be drawn to the scent of that wound. That’s why it is so important to NOT PRUNE your oak trees for the five-month period from February 1 through June 30. Yes, springtime is when we get out into our yards and want to do things. Please do anything other than prune your oaks. And don’t let any commercial tree service/arborist try to convince you otherwise. Now, if you absolutely must prune an oak because it’s rubbing on your roof or has been snapped off by a tall vehicle such as a garbage collection truck, make a clean cut and spray or paint that cut IMMEDIATELY with tree paint or other latex paint.

 

Spread through Roots

Oaks tend to grow in clumps with interconnecting roots. The fungus may be transmitted from one tree to another through these root connections. A close example may be seen on Millwright Parkway at Timbercrest. Although transmission of the disease is relatively slow through roots, nevertheless it will continue to spread year after year at an average rate of 75 feet per year. There are several expensive ways of trying to stop it, deep trenching for example, but let’s hope we don’t have to deal with that.

 

Spread by Humans

Unseasoned firewood (dried for less than one year) from oak wilt infected trees should not be brought onto your property and stored. If you don’t know the source of the wood, don’t even consider bringing it near your home. Your healthy trees don’t need to be exposed to possible contamination.

 

Learn More

I’ve only just scratched the surface of this nation-wide oak wilt threat. Austin has already lost more than 10,000 oaks to the deadly, infectious disease. What would your yard look like without any oaks?

To discover more about identifying and managing oak wilt, please check out these Texas websites:

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https://tfsweb.tamu.edu/OakWiltFAQS/

texasoakwilt.org/