I need to kill existing grass and sod the service area in front of my home (between sidewalk and curb) using Round-Up or the equivalent, but there are two medium sized trees in the area. Can I safely do a "surface" grass kill without harming the trees?
Depends on the type trees. I use it quite a lot and have found that cedars don't like it at all. Sweet gum may show some leaf browning if spray gets on any suckers. However, most hardwood trees tolerate it quite well.
No, the tree, assuming it's established and not recently planted, will suffer no ill effects other than the sprouts dying if you get it on them, and that doesn't usually matter. Especially around the base of the tree it won't hurt much. Just be sure to spray where you intend, not all over the place. Take your time and be accurate as reasonable. I kill of my cherry tree sprouts like that every year. The tree's thriving. Whatever the killer touches will absorb it, and pull it into the plant. Trees however are quite large and older healthy trees won't be affected by the little bit of roundup.
Roundup is not a universal plant killer - some plants are just not affected by it. The cambium layer in a plant carries nutrients & water back & forth within the plant. This layer is between the bark and the wood. If the bark is dense and tough, it protects the cambium layer from roundup. If the bark is soft, like cedar, roundup can be absorbed through the bark much like through leafs. In your case, instead of drilled holes you may have done better to peal the root bark and apply full strength roundup to the pealed area. But then bottle brush may be one of those plants that roundup doesn't affect.
The bottle usually says "do not apply over 80F" or something like that. If you spray when it is too hot, you may experience the spray evaporating from the grass under the tree, and depositing on the leaves of the tree. You may injure or even kill the tree.
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