Question
What kind of worm would defoliate a willow oak tree and how do you get rid of it?

Answer
There are several insects that will defoliate a willow oak tree. Most are caterpillar type. They all can be controlled with the use of an insecticide called Orthene. This is sprayed on the foliage and kills the insects as it feeds or walks through the insecticide. All the foliage will need to be sprayed to get complete control. IF they caterpillars seem to crawl down the trunk the main trunk can be sprayed and as they migrate to find a place to build a cocoon they will be killed. This will work on most of the caterpillar type but not on one called a sawfly. Sawflies usually feed in groups where caterpillar type tend to feed singularly. On large trees the spry is difficult to get on the foliage but the good thing the feeding will not kill the tree and it will leaf out next spring as if nothing happened. Insects that defoliate late in the year have very little effect on the health of the tree especially hardwood tree. So if you can not spray the foliage do not worry just try the spray on the trunk and kill what you can knowing your tree will not die from the defoliation.