Destructive fungus is spreading in area oaks

By I’sha Gaines
Fort Worth, TX (June 15, 2007)- Louis Collins was getting three oak trees pruned at his house in Ridglea Country Club Estates when his yard man handed him several green leaves with telltale brown veins that had fallen even as spring rains greened up the rest of the landscape. “You got a problem,” the man told Collins, warning him that the trees had symptoms of oak wilt.

Collins spent $1,200 to have the roots on two live oaks and one red oak injected with a fungicide that can control the disease. Letting the trees perish, Collins said, could lower the property value on his west Fort Worth home by $30,000 and “would make my yard look diluted.”
Spread by a fungus, oak wilt primarily attacks live oaks and red oaks and affects areas where those trees are most plentiful. “Oak wilt is the most devastating tree disease in Texas,” he said. “Once it’s in an area, it’s basically there until it runs out of trees to kill.”
White oaks, such as post, bur and chinkapin oak, are more resistant to the disease. Post oaks, for example, abound in Arlington. That helps explain why Stacie Baldwin, Arlington’s urban forestry and land manager, has documented only three cases of oak wilt in the city over the past 10 years.
Most oak wilt cases are found in Fort Worth and Grand Prairie, said Courtney Blevins, a regional urban forester with the Texas Forest Service’s Fort Worth office.
First identified in the 1940s in the upper Midwest, oak wilt arrived in North Texas in the late 1960s. The disease is spread by an airborne fungus, through roots and sometimes by the nitidulid sap beetle, which is attracted to the spores red oaks create underneath their bark in late fall. The disease primarily attacks live oaks and red oaks. Spores from the fungus clog a tree’s vascular system and prevent nutrients from nourishing limbs and leaves.
Live oaks: The tree begins to have a “sickly” look to it — such as the appearance of leafless, dead branches. It drops more leaves than it should during odd seasons, such as summer. Leaf veins turn brown or yellow, and infected trees typically die within a year.
Red/post oaks: Leaves quickly turn brown or pale green. They have autumn-like coloration during summer, and infected trees die within six months.
Four ways to prevent oak wilt:
1. Avoid pruning and wounding oaks from February through June, when the sap beetle is most active. Cover pruning wounds with latex spray paint or pruning paint.
2. Cut root connections between infected oaks and form a trench around the trees to prevent tainted roots from mingling with healthy roots.
3. Have an oak wilt specialist or arborist inject fungicide into tree roots. Injection prices depend on the oak’s diameter. If oak wilt is found within 150 feet of your trees, re-treat them in two to four years.
4. Infected trees may be cut for firewood, but leave the stacked wood where the tree stood. Wrap infected wood in clear plastic to keep the fungus from infecting other trees and avoid shipping it.
Related Resources:
Texas Forest Service
Urban Renewal, Inc.
Fort Worth Star-Telegram