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, because they will 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:
One of the basic, and most successful, methods of mother nature’s propagation of the live oak are these root sprouts. In their native environment single live oak trees are seldom found. Rather they are congregated in groups of trees called copses. Perhaps a squirrel planted the original acorn from which this copse emerged and the ensuing tree sent up many oak sprouts. Of that many some succumbed to the browsing of domestic and wild animals such as cattle and deer which find them very tasty, and some didn’t make it for other reasons. Those that survived became the copse, all connected to a common root system.
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.
So really the answer is that we just have to learn to live with them. How you do this is a personal preference. Some plant Asian Jasmine in the same area because of its similar leaf appearance and periodically cut off the oak sprouts as they grow taller than the ground cover. Some thin out the canopy of the trees, allowing more sunlight to filter down to the ground enabling St. Augustine or Zoysia grass to grow. Then the offending oak sprouts growing in the grass are frequently mowed off. I have also seen them used as a ground cover just by keeping them mowed