QUESTION: "We have about 300 live oak trees on our property, and almost all are covered with what I term "boles" on the leaves. Not just a few; but literally many hundreds. Do these "critters" harm the trees? Is there a cure? If so, what should we do to eradicate them?" – Len & Janice Westra
ANSWER: Any insect or beetle that is foreign to the tree will harm it. You may try some of the insecticides like Sevin or Malathion. However, before you do anything, I suggest you try checking with the agricultural extension agent in your area. If it a problem you are having then it is quite likely that someone else in your area is having it too, and the extension agent could have a solution to the problem. From your description and the picture you sent me, your "critters" could well be spider mites, but your extension agent will know for sure.
I did find a useful web site you might want to check out. It's called "All About Oak Trees". The web address is http://www.oak-tree.com/oak-tree-insects-and-disease.html. The Oak Tree site has descriptions and pictures of various insects and diseases that affect oaks.