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Saturday - December 25, 2010

From: Austin, TX
Region: Southwest
Topic: Diseases and Disorders
Title: Possibility of oak wilt in red oak in Austin
Answered by: Barbara Medford


I planted a Red oak tree in Austin January 2008. It was container grown but decent size, over 15ft tall. This summer (2010) its leaves turned color as if it were fall and started dropping. I started deep watering it again thinking maybe it was too dry. I also noticed wounds in its bark towards the bottom; including holes in the mid to upper part of the trunk. I've read a little bit about oak wilt from your resources. It sounds like that could be it. I hate to remove and kill the tree unless I have to do so. I also don't want to endanger the many beautiful oak trees in the neighborhood. Please give me some advice.


We are sorry to hear about your sick tree. Red oaks are, unfortunately, one of the most prone of the oaks to Oak Wilt. That does not mean, however, that anything that goes wrong with an oak is Oak Wilt. We can't say that Oak Wilt was the cause of the wounds in the bark, but the insect (nitidulid beetle) that transmits the disease from one tree to another loves to find wounds and cracks in the bark where the beetle can feed on the sap. The beetle itself does no harm to the tree, but carries on his body spores of the fungus that causes Oak Wilt that he has picked up from infected trees. So, the first thing we would ask you to ask yourself: Which came first, the wounds and cracks or the decline in the oak? This, in itself, won't change the outcome in your particular tree, but it is important for everyone who is growing live oaks or red oaks to know that any wounds to the tree by lawn equipment, including mowers and weed eaters, should be avoided, year round. Pruning of an oak should only be done in the hottest part of summer and the coldest part of winter, times when the beetle is not active.

Thank you for reading up on oak wilt on our website; some of the links in this excerpt from a previous answer on the same subject may be repetitious, but you should certainly read them all to get as many clues as you can:

"Read this article from Texas A&M Horticulture Things You Should Know About Live Oak Decline. We don't know what caused the wound, disease or a blow from some mechanical source, but we know the sap being available between February 15 and June 15, when the nitulidid beetle is active, is bad news. This beetle also feeds on the sap, but if the little beastie has been visiting an oak tree with Oak Wilt, he will carry the fungus for Oak Wilt on his body, and infect the wounded oak. 

So let's get back to the wounds and the insects visiting the wounds. From Eric Becker of the Texas Forest Service:

"After being stressed by the drought many of our oaks were further damaged by Hypoxylon and borers.  As soon as you hear someone say the bark has fallen off, you can bet that their drought stressed tree has hypoxylon cankers (first brown and powdery, and then a silvery crust) and the prognosis is not good."  

Go to the  TAMU AgriLife Extension Plant Pathology page to find three fact sheets about hypoxylon:  Hypoxylon Fact Sheet #1, Hypoxylon Fact Sheet #2, and Hypoxylon Fact Sheet #3. 

If you live in the areas north of a Wimberley to Kyle line then there is the chance that oak wilt could be at play as well.  Trees damaged by oak wilt can also display hypoxylon cankers, so then we look for the pattern of mortality, groups of oaks dying side by side, and the brown vein leaves.  Drought mortality accompanied by hypoxylon cankers usually occurs on one or two oaks over here and another two or three over there—the sick trees are scattered about with healthy ones in between."

However, you should visit the Texas Oak Wilt site to familiarize yourself with the symptoms, prevention and treatment of the disease."

You are in the Austin District of the Forest Service, and you will find Mr. Becker's office contact information at this page in the "Getting Help" section. You need to do this as soon as possible; there is no cure for Oak Wilt and if it has already invaded some of your trees, others in your area are at risk, also. We cannot diagnose disease nor recommend treatment from a distance. You need to get help from specialists in tree disease, and certainly the Forest Service is a good place to start.


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