Oak wilt is a fungal disease that kills live oaks and red oaks in Texas. It's far more widespread in Central Texas than around Houston, but it's worth taking seriously anywhere oaks grow, because once a tree is infected there's no reliable cure.
The fungus is spread in two main ways: through connected roots between neighboring oaks, and by small sap beetles that carry spores from infected trees to fresh wounds on healthy ones. Those beetles are most active in spring, which is why fresh cuts in spring are the biggest risk.
The Texas A&M Forest Service recommends avoiding oak pruning from February through June. The safer times are the coldest weeks of winter and the hottest stretches of summer, when the beetles and the fungal spore mats are least active.
The same guidance says to paint every oak wound right after it's made, any time of year, with a light coat of wound dressing or latex paint. That includes pruning cuts, broken branches, and even damage from a mower or a trimmer line against the bark.
Emergencies don't wait for the calendar. If a storm cracks a big limb over your roof in April, it needs to come down. In that case we make clean cuts, paint them immediately, and leave the rest of the pruning for a safer month.