For the most part, the Post Oak is a hardy tree with few diseases affecting it. It is sometimes bothered by Chestnut blight or oak wilt.
There is one insect in particular that causes damage to the twigs and branches, namely the "Twig Pruner."
July 11, 2008
By Howard Russell
...The twig pruner (click here) cuts through the twig from the inside, but leaves the bark intact. For a short time the injured branch remains on the tree, but eventually succumbs to the wind, breaks off and falls from the tree. A small oval shaped hole in the end of the branch is a tell-tale sign of the twig pruner. Look closely for this hole because the larva usually packs the opening with a frass plug to keep out predators and other unwanted guests. Twig diameters at the point of the cut usually range from about three-eighths to three-quarters of an inch. Common host trees are reported to include oak, hickory, pecan, walnut, basswood, redbud and hackberry.
Reports of the life cycle of the twig pruner vary somewhat. As we understand it, the females lay eggs in small twigs near the ends of live branches in late spring. The larva eats the inside of the twig, then bores into the center of the branch and tunnels downward. When nearly fully grown, the larva severs the twig or branch by tunneling in circles from the center outward to the bark. Pruned twigs or branches soon break and fall. The larva continues to feed in the severed twig until it pupates. Winter is passed in the severed branch....
