Not much you can do at this point. You'll have to wait until the tree "tells" you what will happen next.

Joe,

It depends on the size of the tree. Glyphosate will generally do an excellent job killing young trees if all the foliage is covered. Larger trees can tolerate it more.

It's a good sign that foliage is only dead on one side. Since glyphosate is systemic, it's likely the tree didn't absorb enough to kill it, else all the foliage would be dead.

It will help some if you keep the tree well watered. That's a slight antidote to glyphosate. Just don't water the tree so much the roots start to rot, otherwise you'll compound the problem.

Thanks, Olpea. I'll take any good news I can get. It's rained three days in a row, so I may be in good shape.

This tree is about 20 years old, and would have been about 15 feet tall. But it got halfway knocked down in a storm so all the branches are easy to reach. It would be difficult to replace, to say the least.