I have a lot of nice sized oak trees. I have pin, black, and chestnut. Every once in a while one of them puts out sprouts all over the trunk and starts looking like a green pillar. How do I keep that from happening?
Oak runners can be stopped by stripping off the leaves, check them weekly and rub off any new sprouts. It takes a few months, longer for Red Oak than Live Oak. do not cut them, the come back thicker. If you notice in nature you do not find many trees with sprouts. that is because deer, goats, cattle etc. eat the new sprouts. Once the sprouts become brittle break them off.
Unfortunately, there is nothing you can do to prevent them from growing sprouts. Oak trees occasionally propagate in the wild through root sprouts and that's what these are (discounting when it's a fallen acorn that has sprouted). Since these sprouts are connected to the main tree through the roots, using any form of chemical to "burn" them will easily kill the tree. You could however, keep them in check by trimming them often or digging them out.
This page has some good info on oak sprouts:
Being interconnected through roots also has its disadvantages because diseases can propagate through the entire group easily.
They also recommend planting jasmine and trimming the sprouts when they outgrow the jasmine. Another suggestion is to plant grass such as St. Augustine or Zoysia and mow the sprouts along with the grass.