Latex paint on the bottom of the tree may help protect the tree from Roundup. I use a backback sprayer when I spray Roundup around my apples or peaches to control where the spray goes. Its a lot more work than spraying from the tractor, but I can’t afford to take any chances. The large growers who spray Roundup with booms are bound to hit some suckers or tree bark.
I have not seen a problem from Roundup use so far, but I cut back when I saw a presentation on Roundup damage on apple trees at a grower meeting a few years ago. I got the impression that the experts are not sure if the damage is caused by hitting the bark, the foliage or build up of the glysophate or other ingredients contained in the spray in the soil
The presentation on Roundup damage caught my attention because most growers thought it was perfectly safe and did not exercise enough caution when they used it