Oak wilt devastating Central Texas trees
Landowners educating themselves for methods in tree protection

By MANDY SPIKES | Central Texas Edition

Renee Burks, with the Texas Forest Service, shows the proper way to use a fungicide injection when treating an oak tree for oak wilt. The demonstration took place during the oak wilt seminar, which was held on Sept. 16 at McLennan Community College's Highland Ranch, located in Bosqueville. -- Photo by Mandy Spikes

September 25, 2003 -- Oak wilt, a fungus which prevents movement of water and nutrients from the roots of an oak tree to the foliage, has been detected in over 54 counties with primary problem areas occurring in Central Texas. After contracting the fungus, the symptoms of the disease may occur fairly rapidly in some cases, while other cases might take several weeks or months.

Renee Burks, with the Texas Forest Service, recently spoke to participants about oak wilt control and prevention at the Oak Wilt Seminar, which took place Sept. 16 at McLennan Community College's Highlander Ranch, located in Bosqueville.

"Oak wilt and oak decline are not the same thing, although the terms have been used interchangeable for many years," began Burks. "Oak wilt clogs the living tissue of the tree. In affect this causes the tree to literally starve to death because water and nutrients can't get to it. Oak decline, on the other hand, is the gradual deterioration in the general health of the tree. Decline does not actually kill the tree but weakens it making the tree more susceptible to other pests."

Another factor that needs to be taken into consideration, Burks stated, is the type of species of oak being looked at. "Some species of oaks are more susceptible to oak wilt than others. Live oak, Texas red oak, and blackjack oak are more susceptible to the disease. Post oak is considered less susceptible."

The best place to look for oak wilt symptoms, according to Burks, is on the ground underneath the tree. "There are several leaf patterns which will indicate the presence of the fungus. The leaf pattern to look for will have the veins being a discolored yellow or brown color while the rest of the leaf will remain green.

"During periods of extreme heat and drought, the tree often doesn't produce these symptoms. Instead, it will turn brown relatively quickly and usually hold on to its leaves. Should this occur, it's best to contact either the Extension agent in your area or contact the Texas Forest Service for disease confirmation."

She gave several factors that must exist in order for oak wilt to occur. First, there must be an infected red oak in the area, either in the form of a standing tree or firewood. This oak must have produced the fruiting body of the fungus. A nitidolid beetle must land and feed on the spores and then fly to a nearby tree that has a fresh wound. Once the beetle lands on the wound, spores are implanted and the disease will move through a system of roots from one live oak to another until the disease runs out of living tissue.

"This makes it crucial to put sealant on the fresh wound as soon as a cut is made. There is a narrow window of opportunity for an insect to come in and put the infection in the tree. This is usually 24 to 36 hours after the cut is made. After 36 hours, the tree starts to heal itself. During this time the danger of infection is minimized."

Once oak wilt becomes established, Burks gave several options for the landowner to choose from including letting nature run its course, attempting to sever the connective root systems between sick trees and healthy trees, and injecting surrounding trees with a fungicide treatment.

"The treatment will not stop the movement of the disease, but it will help the tree survive the fungus when it does contract the disease. Also know that it is not always a one-time treatment. Should a treated tree begin showing the signs the following year, an additional injection is recommended."

She said that Alamo is the only fungicide available for the treatment of oak wilt. "The active ingredient in Alamo is Propiconazole. The rate of treatment should be one liter of water and 10 milliliter of chemical per inch in diameter. The cost for Alamo is about $300 per quart or 59 inches in diameter."

Burks gave different preventative measures when dealing with oak wilt. These included avoid wounding the oaks between February and June. This is because beetle populations are at their highest.

"Paint any and all wounds with pruning paint. If you can't find pruning paint, then use spray paint or latex paint. Just use something that will cover and seal the wound within the first 36 hours.

"Cover your oak firewood with a clear plastic cover for at least one season. Burning firewood that has been killed by oak wilt isn't the problem. This problem is in the storage of the firewood."

The last preventative measure she stated was beware of your neighbor's trees. Watch them for possible signs of the problem.