Question
I had a 15 gallon Live Oak planted 3/2/07. I wanted to control the grass growing in my tree ring and put a grass and weed killer on it. I didn't realize it until after wards that I picked up the 3x concentrate weed killer. Now, my live oak leaves are turning brown and falling off. Is there hope for this tree? Thanks!

Answer
Weed and Feed" or plain "weed" fighting chemicals can cause serious problems for trees and shrubs.  These materials are generally considered safe to humans, pets, and wildlife, if label directions are closely followed.  However, many weed control chemicals are not as safe to the desirable trees, shrubs, and ornamentals growing in the lawn or in surrounding planting beds.  The problem is not really with the weed killing products, but with us... those applying the products.  We frequently fail to read and fully understand the precautions given on the label.
Many products, especially those containing the active ingredient dicamba, advise against use in the root zone of desirable trees, shrubs, and other ornamental plants.  Damage often occurs when gardeners don't realize just where the root zones of these plants are located.  

Trees and shrubs are not tap-rooted (with a few exceptions). Roots expand laterally out from the trunk where there are larger "pipeline" roots that divide and subdivide, becoming smaller with each division until the very ends where the fine-feeder roots are located. The fine-feeder roots are responsible for absorbing water and nutrients from the soil.  The roots of most trees are found in the top 18 inches of soil, with over 50 per cent of their roots found in the top six inches of soil.  They're situated in this top layer of soil because that's where they can get the air, nutrients, and water they need for growth and survival.

Roots go out much further from the tree trunk than once believed.  It was once thought that most of the fine-feeder roots were located primarily in the drip-line zone. This is the area beneath the reach of a tree's side branches... the place where rain "drips" off a tree.  However, research has revealed that the root systems, especially the fine feeder roots, extend out laterally much further from the trunk.  In fact, tree roots often extend out from the tree trunk as far as the tree is tall... or even further.

There is not really much that can be done. I would say the tree has a less then 50% chance of living. I would try heavy watering the area under the tree--almost to the point of flooding the area with water. This may dilute the herbicide enough to allow the roots to survive.