The oak wilt window
Oak wilt spreads two ways: through root grafts between neighboring oaks, and by sap beetles carrying spores from a fungal mat to a fresh wound. The beetles are active in spring and early summer, and they are drawn to the smell of freshly cut or wounded oak.
The practical rule in our region is to avoid pruning oaks from roughly April through July. Late winter, when the tree is dormant and the beetles are not flying, is the right window. Pruning in August through early winter is generally acceptable.
Storm damage does not follow the calendar
If an oak limb breaks in June and is hanging over a driveway, it has to be dealt with regardless of season. In that case, the cut surfaces should be treated promptly — a wound dressing is not normally recommended for general pruning, but for oak during the high-risk window it is a specific exception that some arborists use.
The important thing is to remove the broken material, make clean final cuts rather than leaving stubs, and not to prune neighboring oaks for the sake of tidiness in the same month.
Why root grafts matter
Oaks of the same species growing near each other often share root grafts, which means oak wilt can move from tree to tree underground without any beetle involved. That is why an infection in one oak can take out a cluster, and why removal of an infected tree usually includes severing root connections to the neighbors.
If you have lost an oak to wilt, replanting with a different genus in that spot is worth considering, at least in the short term.
What good oak pruning looks like
Oaks respond well to structural pruning: deadwood removal, thinning of crowded interior growth, and reduction of long horizontal limbs that carry too much leverage. Live oak branches should be cut back to a lateral that is at least a third of the diameter of the piece being removed, so the tree can seal the wound.
Flush cuts and stub cuts are the enemy here. They open a decay column that shows up as a hollow trunk twenty years later, and a hollow oak near a house is a removal.