Arborists Wage War on Tree Wilt
Published August 15, 2008 By AUSTIN KILGORE
Homeowners urged to take steps to protect oak population in danger from migrating disease.
The abundance of enormous trees that line the yards in well-established neighborhoods like the Park Cities and Preston Hollow are one of the greatest natural resources in North Texas. But the increased presence of a dangerous pathogen is taking a toll on the oak tree population.
Oak wilt has been wreaking havoc in Central Texas for decades, and has recently begun to migrate north. It is a vascular disease that causes the water-conducting tissues in oak trees to plug up and prevent the flow of water and nutrients throughout the tree, causing leaves to wilt and the tree to die.
Arborist Steve Houser, chairman of the city of Dallas Urban Forest Advisory Committee and owner and president of Arborilogical Services, estimates red and live oaks, the two trees most susceptible to oak wilt, make up as much as 30 percent of the tree population in the region, and more than 130 oak wilt infection centers have already cropped up across the area.
“These sites can be entire blocks, and there’s a good part of our oak population that’s already been affected,” he said.
Oak wilt spreads in two ways. Both the red and live oaks can contract the disease through the extensive root systems that spread for yards beyond the footprint of a tree. The roots graft together, and infected trees pass the disease along.
“If the roots touch each other, it can transfer the disease from one tree to the next tree, and when it gets started in an area with a lot of oak trees, it can go from one to another to another,” Houser said.
Red oak trees can also contract oak wilt from sap-feeding beetles that carry the disease to the trees as they feed on exposed sap from wounds on the tree.
Oak wilt is so dangerous that it can kill a centuries-old tree in less than six months.
The loss of oak trees in a home’s yard doesn’t just affect the quality of life for homeowners and their loved ones. John Giedraitis, Texas urban forestry coordinator for the Texas Forest Service, estimates well-established trees make up for 10 to 20 percent of the value of a property. He recommends homeowners protect their investment by only hiring qualified professionals to care for trees.
Hire professionals that are insured for liability and personal injury, Giedraitis said. The tree service will cost more, but the insurance protects the customer from liability if something goes wrong.
There is no state-issued license for arborists, so Giedraitis recommends hiring one that’s certified by the International Society of Arboriculture. He also suggests asking a company to provide references from past clients.
“If the tree looks really sick and they tell you they can save it, call somebody else because the odds are they can’t,” he said. “There’s no magic Lazarus formula.”
The most effective way to stop the spread of oak wilt from beetles is by not pruning trees from February to June. The beetle population is highest at this time, and the exposed wounds from pruning leaves them vulnerable to infection. If pruning is absolutely necessary, after damages from a storm, or if other damage occurs, the wounds should be sealed with a special spray-paint available at nurseries.
When an oak wilt outbreak occurs in a neighborhood, it is possible to manage it. The Texas Forest Service recommends disrupting root systems with trenches to prevent the disease from spreading through the roots. Infected trees and their roots should be removed as soon as possible, and while they are safe for use as firewood, they should be left to cure away from healthy trees for at least a year.
Tightly covering a stack of firewood logs with a plastic tarp is the best way to ensure beetles don’t carry the disease to healthy trees. If an area is facing an oak wilt infection, trees in danger of catching the disease can be treated with a fungicide to fight off the disease as it spreads. Some infected trees can also benefit from fungicide, but they must be treated in the early stages. The fungicide won’t kill the disease; it only suppresses the symptoms and prolongs the life of the tree, and must be reapplied every two to three years.
Giedraitis and Houser both advise that all of these steps be done by a qualified professional with oak wilt experience.
While limiting pruning and treating trees with fungicide will slow down oak wilt, even the healthiest trees are susceptible to the disease.
Two years ago, the city of University Park's Park Services department dealt with a rash of oak wilt at Curtis Park. The city hired an arborist that specializes in oak wilt and treated the trees that could be saved and removed the ones that were too far gone.
UP public information officer Steve Mace said other instances have come up where homeowners have hired private contractors to do similar work at their homes, and the city is constantly watching for new infection centers to crop up.
Highland Park parks director Ronnie Brown said the town has never had an oak wilt problem with any public trees, but that doesn't keep his staff from limiting pruning and painting over open wounds. Equipment is also thoroughly cleaned to prevent any accidental spread of a disease.
To provide support for the fight on oak wilt, Houser’s committee is working with the city of Dallas to create an office of urban forestry. This office would oversee the protection of oak trees on city land and provide a management plan to control oak wilt citywide. Houser briefed the Dallas City Council’s quality of life committee before the summer hiatus, and will address the full council within the next month.