(I'm presuming this is a reasonably mature tree, not just a five to ten foot adolescent, in which case my answer changes!)

Given the amount of RoundUp versus the size of the tree, it's simply going to act as a minor growth inhibitor (RoundUp being an auxin). It's not of that much concern.

That having been said, I never do it. Cut the tree suckers first, then spray, to lower the amount absorbed by the tree.

Thanks Morpheus. I was going to cut them anyway since they’re starting to get out of hand. And yes, it is a mature tree.

Any solution to suckers that just keep popping up in the mulch ring around the tree? I swear I sprayed everything on those things, they keep coming.

Maybe you should ask a sucker question in the trees forum.

And if you find something out, let us know. I've got two that sucker like mad.