Question
Our pin oak tree has what look like spider webs all over the leaves (not on the bark).  There are no spiders to be seen, but there are little brown seed looking things in the webs.  Are these webs harmful?  If so, how should we treat the tree?  Thanks!

Answer
Sounds like fall webworm an insect.
The fall webworm is a widely distributed native pest of shade trees and shrubs and appears from late summer through early fall. It feeds on almost 90 species of deciduous trees. The fall webworm constructs its nest over the end of the branch. The large conspicuous webs contain caterpillars, dead partially eaten leaves, and fecal droppings.

The caterpillar constructs the web in late June- September then drops to the ground to pupate. The adult emerges the next spring and lays its eggs on the branches. what you are seeing is the webs that have been left by the caterpillar and the "brown seeds' is insect frass.

The larval stage of this pest skeletonizes and consumes leaves inside the protection of a tent-like web that they enlarge as they require additional food and grow. They may defoliate a tree occasionally, but rarely kill it. On shade trees webs usually occur on occasional branches. They may not injure the tree appreciably, but they reduce its ornamental value.

There is no need to treat since the caterpillars have gone and no more damage will be done. IF the webs return next summer the caterpillars can be sprayed then with any contact insecticide. Otherwise I would not be concerned with fall webworms since by the time they defoliate a tree the tree has started to shut down for the winter.