In short
- Don't prune or wound oaks from February through June.
- Paint every cut or wound on an oak right away, any month. Any paint works.
- Lawn mowers and string trimmers wound trees too. Keep them away from the trunk.
- Yellow and brown veins on live oak leaves can be a sign of oak wilt. Ask a certified arborist.
What oak wilt is
Oak wilt is a fungal disease that blocks the system a tree uses to move water. According to Texas A&M Forest Service, it has killed millions of trees across 76 Texas counties. Live oaks and red oaks are the most affected.
Why February through June
Above ground, the fungus travels on small sap-feeding beetles. Red oaks that died of oak wilt the year before can grow fungal mats under their bark. The mats have a fruity smell that draws the beetles, and the beetles carry spores to fresh wounds on healthy oaks.
Those beetles are most active in late winter and early spring. That's why Texas A&M Forest Service recommends not pruning or wounding oaks from February through June.
When to trim oaks
Texas A&M Forest Service: don't prune or wound oaks from February through June.
- Jan: OK to trim
- Feb: avoid
- Mar: avoid
- Apr: avoid
- May: avoid
- Jun: avoid
- Jul: OK to trim
- Aug: OK to trim
- Sep: OK to trim
- Oct: OK to trim
- Nov: OK to trim
- Dec: OK to trim
All year: paint every cut on an oak right away.
Paint every wound, all year
A fresh wound is an open door. Texas A&M Forest Service recommends painting every wound on an oak right away, in any month, to create a physical barrier. Any kind of paint works.
A "wound" is more than a pruning cut:
- Pruning cuts and broken branches after a storm
- Construction and land clearing
- Lawn mowers and string trimmers hitting the trunk or surface roots
If a branch is a safety risk between February and June, for example after a storm, it may not be able to wait. In that case, paint the cut immediately.
How it spreads underground
In live oaks, oak wilt also moves through connected roots. Texas A&M Forest Service says it can spread about 75 feet a year this way, which is why it often moves from tree to tree down a street. Stopping it underground, with root trenches or fungicide injections, is a job for a certified arborist.
Signs to watch for
- Live oaks: leaves with yellow and brown veins (called veinal necrosis). It's harder to spot in spring, when live oaks swap their old leaves for new ones.
- Red oaks: leaves turning red or brown in summer. A red oak can die within about a month of infection.
If you're not sure what you're seeing, Texas A&M Forest Service recommends contacting a certified arborist. And don't move firewood from oaks that may have died of oak wilt.
City of San Antonio rules
The City of San Antonio has its own tree rules, including dates for oaks. Check them before any oak work.
Need a trim?
Tell us about your trees and we'll come give you a free estimate at your home. See our tree trimming service.
Sources
- Texas A&M Forest Service, “Oak wilt disease threatens Texas oaks in spring” (Feb 2019)
- Texas A&M Forest Service, “Prevent the spread of oak wilt in Texas this spring” (Mar 2021)
- AgriLife Today, “Texas A&M Forest Service's pruning tips to prevent the spread of oak wilt” (Feb 7, 2024)
- Texas Public Radio, “Protecting your trees from oak wilt” (Jun 2026, with the City of San Antonio's arborist)
Checked Oct 18, 2026. Water rules and dates can change: always confirm with the source.