By Dane Anderson, Staff Writer

Now is the time to prune oak trees, according to the Texas Forest Service.

Foresters recommend that the pruning be done only in the hottest part of summer, from July 1 through Sept. 30, or during the coldest days midwinter, from Dec. 1 through Jan 31. 

Any cut or breakage to an oak tree should be sealed immediately with a pruning paint, recommends Eric Beckers, a Travis County project forester with the Texas Forest Service. 

Oak Wilt disease, a fungal infection that has destroyed thousands of oak trees in Texas, can be spread by sap-feeding beetles that are attracted to the scent from a wound on an oak tree. Beetles that feed on an infected tree pass the disease on to other trees whose wounds they enter. 

Experts recommend that property owners carry pruning paint with them when pruning oak trees, and that they paint cuts on trees as soon as they are made. Within four days, it is too late to seal a tree cut. 

“The fresher the cut, the more it smells,” said Dave Lavrinets, assistant manager of Barton Springs Nursery. “If there is a beetle in the area, he will head for that smell.”

Lavrinets said that his nursery and others carry pruning sealer in paint form that can be used on lower tree branches and also sealers in spray form for use with extending pruning poles used on higher branches.

As property owners prune, they become more aware of weak trees and alarm about oak wilt disease increases. 

“Concern about the disease comes around from time to time, especially when it claims a dramatic set of trees,” Beckers said. “But the truth is that it is always out there.” 

Oak wilt is also spread through the root systems of connecting oak trees, especially live oaks. The disease can travel 150 feet each year through oak root systems. The only effective way of stopping the spread of oak wilt from an infected tree to other surrounding trees within a 150-foot area is by digging trenches around the tree that sever the root system. 

“In an urban setting, trenching can get very expensive,” said Beckers. “Trenching is used more as an option by ranchers.”

Fungicide injections do not stop the root transmission of oak wilt between trees, but can be used to treat an infected tree. The faster a homeowner diagnosis oak wilt disease in a tree, the better the chances of saving the tree. If more than 30 percent of the crown of a tree is affected by the disease, fungicide is unlikely to work, said Beckers. The use of fungicide injections is most effective on non-symptomatic trees within 150-feet of infected trees.

Beckers said there are a number of active oak wilt disease centers in the Westlake area, including sites in West Lake Hills and the Westwood neighborhood. 

“Most oak wilt disease centers don’t just dissipate,” he said. “The best long-term solution we have to the problem is the planting of a more diverse range of trees.”

Another concern of local arborists is a fungus called hypoxylon that can hit drought-stressed trees of any kind. 

“It’s airborne and will affect most types of trees,” said Keith Brown, an arborist with Austin Tree Expert and a contractor for the city of Rollingwood. “When a tree is infected, the bark begins to slough off and a large gray or brown canker develops. Typically, the tree will completely die back in as little as a few weeks.”

The best defense against hypoxylon is to keep trees healthy by watering and fertilizing. 

“Hypoxylon waits for an opportunity to finish off a weakened tree,” warned Beckers. 

Both Beckers and Brown say that homeowners that notice trees with a significant number of sick or dead branches should contact a professional arborist for a diagnosis as soon as possible.

To learn the warning signs for oak wilt disease, visit the Texas Oak Wilt Information Partnership Web site at texasoakwilt.org. To learn more about hypoxylon, search the Texas Forest Service Web site at txforestservice.tamu.edu.