Oak wilt is a real disease hitting Texas trees

By JULIET BRISKIN | Central Texas Edition

Renee Burks of the Texas Forest Service discusses oak wilt at the Comanche Farm, Ranch and Dairy Day. According to Burks, oak wilt and oak decline are not the same disease. -Staff photo by Briskin

April 4, 2002 -- Oak wilt and oak decline are not the same disease according to Renee Burks of the Texas Forest Service. "These two terms have been used synonymously for years, but they are two totally different ball games," she explained during a presentation at the Comanche Farm, Ranch and Dairy Day on March 28, in Comanche.

"Oak decline is an actual condition. It's like a common cold on the tree," said Burks. "It is generally caused by a stress such as building a new driveway over the root system of the tree. You will have a limb die this year, another die the next. It is a progressive decline like us when we start getting older and falling apart."

According to Burks, oak wilt is an actual disease. "It is a vascular fungus," she said. "It literally clogs up the arteries of the tree and prevents the water from getting from the roots to the foliage where it is needed."

Currently there are approximately 68 counties in Texas that have oak wilt. "It has made it to Houston. It has made it to Lubbock, Amarillo and El Paso," she said. "But the main concentration of the disease is in the I-35 corridor in the Hill Country." She went on to explain that the disease is found outside Texas, but it attacks different species of trees and acts differently than it does in Texas.

An example of an oak leaf showing the signs of oak wilt. Burks stated that if a homeowner sees this type of veinal nicrosis they should know they have oak wilt. Burks did state that one in a million lightening strikes can cause this type of patterning. -Staff photo by Briskin

"Oak wilt attacks three primary oak species that we have," explained Burks. "It affects live oaks, red oaks and black jack oaks. It does not hit any of the white oak family." When a red oak becomes infected with oak wilt it's death is quick according to Burks. "It will turn bright red within ten days to two weeks and she is dead,"she said.

"Unfortunately red oaks do not produce any symptoms that can be quickly identified as oak wilt," she stated. "It looks like someone threw a pot of hot water on the tree. The leaf edges look burned and they literally wilt up. The problem is that these leaf symptoms are often symptomatic of herbicide damage."

According to Burks it takes a bit more detective work to determine if a red oak is actually suffering from oak wilt. It is necessary to assess the entire situation. "How fast did the symptoms appear and were any chemicals used in the general area?" are questions that should be asked stated Burks.

She went on to explain that red oaks are the "bad boys" of the disease. "They can actually produce the fruiting body of this fungus underneath the bark of the tree," she said. "The fruiting bodies are black patches or mats on the bark and they stink like rotten bananas. They are very easy to identify once you see one."

Burks explained that one tree can produce anywhere from 200 to 300 mats. "The primary reason why these mats are so bad is that the smell attracts a nasty little creature called the nitidolid beetle," she said. "They are sap feeding bugs and are attracted to open wounds. You cannot see them with the necked eye but they feed on the mats and then spread the fungal spores to other trees as they feed."

According to Burks live oaks and red oaks often share common root systems. "A good rule of thumb for a live oak is her roots extend out at least three times the height of the tree," she said. "It is not uncommon to see large oaks on either side of a four lane highway that are sharing a common root system."

Burks wrapped up her discussion with ways to combat oak wilt. "Prevention is the easiest." she said. "There are a couple easy ways to do this. Don't cut your trees between February and June unless it is absolutely necessary. If you do cut the wound must be sealed right then and there or you risk attracting the nitidolid beetle."

A tree can only get sick during the first 24 to 72 hours after a wound has been made. If a landowner cuts a limb off a tree it is pointless to come back three days later and seal the wound explained Burks. By then the damage has been done.

"Be careful of firewood that you bring home. If you are sure what the tree was it is fine to cut it up and use for firewood," she said. "There is not a problem with burning the wood what-so-ever. Spores are not spread in the smoke, in fact once the spores are exposed to 85 degree temperatures or higher they are dead."

The problem with firewood comes when red oak is involved and it has an actual fungal mat on it. "If you do not know what type of wood you are bringing home, get a clear painters tarp and throw it over the wood," said Burks. "Put some rocks on the base of it and you have made a little green house. The temperature under the tarp will go above 85 degrees and kill any spores that may exist."

According to Burks the only way to stop the disease once it has infected a tree is through root disruption. "This involves digging a four to five foot deep trench to break up the root system," she said. "Out in the pasture we use a bulldozer but in residential areas we have to use a rock stop."

Burks added that landowners need to be particularly careful of red oaks. "They are beautiful trees but they are a problem with this disease," she said. "If you do plant one in your yard, baby her. If she turns bright red right away, cut her down and get her out of there."