Veinal necrosis
Veins turning yellow then brown
On live oaks, the classic sign is veinal necrosis: the leaf veins yellow and brown while patches stay green. The pattern follows the veins.
Texas Oak Wilt • TOWQ-685
Oak Wilt
The most destructive tree disease in Central Texas. It moves fast, it kills live oaks, and the window to save the trees around it is short. Here is how to recognize it and what to do.
3 to 6 moLive oaks can die this fast
Feb 1 to Jun 30Do not prune oaks
TOWQ-685Texas Oak Wilt Qualified
Field photo
What it is
A fungus that strangles the tree from the inside
Oak wilt is caused by the fungus Bretziella fagacearum. It invades the water-conducting vessels of the tree, which the oak then plugs in self-defense. Starved of water, the canopy browns and dies.
Live oaks are hit hardest because they grow in interconnected groves and share root systems, so the disease races from tree to tree underground. Red oaks (Spanish, Shumard, blackjack) die fastest and grow the spore mats that start new infection centers.
Bretziella fagacearum (formerly Ceratocystis fagacearum)
Warning signs
What to look for in your oaks
These signs point toward oak wilt, but they can overlap with other problems. Only laboratory testing confirms it. If you see them, the move is an assessment, not a chainsaw.
Canopy dieback
Rapid thinning, out of season
A canopy that thins, browns, and drops leaves quickly, often in spring or summer when it should be full, is a red flag worth investigating now.
Live oak decline
One tree failing in a stand
A live oak thinning and dying among its neighbors, like this one on a Central Texas ranch, is the classic oak wilt pattern. Connected roots carry the fungus tree to tree through the stand.
Photos above are from real Central Texas sites. Symptoms shown are consistent with oak wilt. They are not a diagnosis. Confirmation requires an on-site evaluation and laboratory testing.
How it spreads
Two ways it travels
Understanding both is the whole game, because each one calls for a different response.
Underground, root to root
Live oaks graft their roots together. The fungus flows through these natural connections from an infected tree to its neighbors, which is why oak wilt spreads in expanding circles. Stopping it means physically severing those roots with a deep trench.
Overland, by beetles
Infected red oaks grow fungal mats under the bark. Sap-feeding nitidulid beetles feed on them, pick up spores, and carry them to fresh wounds on healthy oaks. That is why a fresh, unpainted cut in spring is an open door, and why timing and wound paint matter so much.
Protect your oaks
The rules that actually prevent it
Most oak wilt spread is preventable. These are the habits that keep it out of your trees.
Never
- Prune or wound oaks February 1 through June 30. This is the peak beetle and spore season.
- Leave any oak wound unpainted, even a small one, even out of season.
- Move or store unsealed red oak firewood. It can carry live spore mats.
- Cut down a suspected oak wilt tree before it has been assessed. The wrong cut can make it worse.
Always
- Paint every oak wound immediately, year round, within minutes of the cut.
- Prune in the safe window, roughly July through January, when you have the choice.
- Use a qualified arborist for oaks, ideally Texas Oak Wilt Qualified.
- Get suspected cases confirmed fast. Early action saves the most trees.
How I manage it
A credentialed, step by step response
As a Texas Oak Wilt Qualified arborist, here is how I approach a suspected or confirmed infection center.
01
On-site assessment
A qualified evaluation of the tree, the site, and the pattern of decline.
02
Lab confirmation
Samples submitted for laboratory testing, because oak wilt is reportable and worth confirming.
03
Trenching
Severing grafted roots with a trench, placed well beyond the symptomatic trees, to stop underground spread.
04
Fungicide injection
Propiconazole injected to protect high-value live oaks. It protects the tree but does not stop root spread.
05
Removal & disposal
Safe removal and proper handling of infected red oaks so they do not seed new centers.
Think you have oak wilt? Time matters
The sooner it is confirmed, the more trees can be saved. Send me what you are seeing and I will tell you straight whether it needs an urgent, on-site look.
This page is educational and does not diagnose, treat, or certify any tree. Oak wilt is a reportable disease in Texas. A suspected case must be evaluated on site by a qualified arborist and confirmed through certified laboratory diagnostics before treatment or removal decisions are made.