Answer: Overspray or drift will kill the vegetation it touches. So if the leaves of your tree caught some overspray they will turn brown and might even fall from the tree. Depending upon the health of the tree, it may or may not replace the dead leaves later this summer. Round Up degrades in the presence of sunlight and air so no residual should remain on the upper part of the tree exposed to drift.
As you've discovered, Round-Up is a non-selective vegetation killer. If you spot spray weeds, it will remain on the weed and travel down to kill the roots. It typically remains in the roots of the targeted weed rather than traveling through the soil. However, if you sprayed the entire area above the root zone of your tree, the Round-Up can translocate into the soil and be taken up by the roots as it is carried by rain water or water from the hose. Once it is in the root system of the tree or shrub, it will remain until it biodegrades. How much damage it can cause will remain to be seen. There's no way to get it out of the tree's system. The Round-Up that was not taken up by plant roots will biodegrade in slightly over 2 weeks when exposed to sunlight and fresh air. Wish I had more positive information to share.
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