Signature oak trees in Hollywood Park and other areas of the city have lost some of their lush foliage to a disease that inhibits water flow and is spreading from rural areas into neighborhoods: oak wilt.
“It’s so depressing when I’m mowing the lawn and walking past 10 stumps,” said Joshua Velasco, who two years ago bought a house a few blocks from his mother-in-law in the incorporated city on San Antonio’s Northside. The previous owners had just removed 12 dead live oaks.
Oak wilt is a vascular disease caused by fungus. Because oak wilt is a primary pathogen, a healthy tree is just as susceptible to it as a sick tree, said Mark Kroeze, an urban forester with the Texas A&M Forest Service. The certified arborist and forester was designated as the state’s expert on oak wilt, disease spread, and invasive species following the retirement of his colleague Mark Duff in February.
Kroeze presented information about the oak wilt pathogen, as well as current research on oak wilt, Wednesday at Laurel Heights United Methodist Church in San Antonio.
Oak wilt was first identified in Wisconsin in 1941, Kroeze said, and Texas was considered safe from the disease because of its summer heat. Locally, oak wilt was first found in Dallas in 1976. Kroeze theorized that oak wilt has probably been present in Texas since the 1930s, but trying to stop the disease is “like trying to stop a freight train with the foot.”
The highest rate of oak mortality in the world is in the Kerrville area, Kroeze said. Currently, Bexar County has 470 acres affected by oak wilt. San Antonio, Helotes, and Hollywood Park, in that order, have lost the most trees to the disease.
Infections are spread from the roots or can be transmitted by insects. Roadways do not constitute barriers to the fungus; only severing the roots stops the disease. Oak wilt lives for five years in dead tree tissue, and for this reason new oaks should not be planted where a tree has died of oak wilt.
“Never use oak firewood,” Kroeze said, because if that wood is infected, moving it to a different location could spread the disease.
Treating trees with fungicide to prevent oak wilt is costly, but losing oaks is far more damaging economically, he said.
“Doing nothing is a really, really bad idea,” he said.
However, treating a tree that is more than 75 feet from a diseased tree is not appropriate because the fungus will not travel that far.
“You don’t realize how impactful [oak wilt] is until you move to an environmentally sensitive area,” Velasco said.
Velasco applauded the efforts of the local government in promoting awareness of oak wilt and providing educational opportunities to learn about the fungus.
“Hollywood Park has taken a proactive approach to dealing with oak wilt and mitigating its effects on the community,” said Hollywood Park City Councilwoman Debbie Trueman, who represents Place 2. “Our trees are one of the town’s greatest assets.”
Trueman said the persistent efforts of Hollywood Park have been rewarded by its designation as a Tree City USA. She credits the City’s Tree Committee with educating residents about oak wilt. The committee includes the state’s recently retired oak wilt specialist, Duff.
Hollywood Park created oak pruning regulations, which require a permit to be displayed while trees are pruned. The map of current locations of oak wilt is updated regularly. Trueman said both residents and commercial tree care workers are required to sign an acknowledgement of the tree trimming regulations before receiving a permit, and fees for permits fund replacements for those who have lost trees to oak wilt.
Oak wilt has also invaded the City of Leon Valley in the northwest San Antonio area. Tom Benavides, a member of the Leon Valley Tree Advisory Board, speculated that oak wilt was introduced to Leon Valley through transportation of firewood from an infected area. Many oaks have died in the Monte Robles and Castle Estates subdivisions where trees more than a century old have long, interconnected roots, helping spread the disease.
Jean Johnson of the Forest Oaks Garden Club said the spread of oak wilt to Leon Valley is being addressed through a tree giveaway program by the City. When the disease was first discovered there, a thorough presentation on oak wilt was included in the public library’s Saturday series. Sandra Keller, president of the Garden Club, said the City has added ordinances to regulate pruning.
Benavides credits Texas Forest Service forester Paul Johnson with starting the Tree Advisory Board to address the invasion of oak wilt. Board members learned to apply fungicide under Kroeze’s guidance.
The Tree Advisory Board applies fungicide to oaks throughout Leon Valley every year and gives away native trees every Arbor Day celebration in conjunction with Leon Valley Public Library. To encourage species diversification, the tree selection includes Anacua, Cordia boissieri wild olive, and species of oak that are more oak wilt-resistant than live oaks.
Correction: This story has been updated to more accurately reflect the state of oak wilt-infected trees Hollywood Park. It has also been corrected to feature the correct spelling of Jean Johnson, Forest Oaks Garden Club, and Sandra Keller.