How do I use RoundUp as a pre-emergent herbicide in a vegetable garden? Do I till it in before planting?

it is not active in the soil..haven't read the label to see if it is labeled to use in a veggie garden, but either way it only kill the plants that are actively growing by treating the leafy parts

edit : remember too that if you use a pre emergent, you won't be able to grow the vegetables by seed, only transplanted stuff

RoundUp is not a pre-emergent herbicide. RoundUp will only kill plants that are already actively growing. It will have no effect on weeds seeds that have not yet germinated.

And you sure don't want to use RoundUp on an area where you're going to plant vegetables. It's highly toxic, nasty stuff, no matter what Monsanto might want you to think.

A good pre-emergent for a vegetable garden would be corn gluten.