I take the backpack sprayer and spray roundup in a one-foot circle around the trees killing the grass.
This year is the third year and it's just a touch up now. Makes mowing easier and quicker.
Been doing roundup also have a gravel driveway that I have to spray.
Tried straight vinegar in my back pack sprayer last year and it works good on the driveway not sure if it would hurt a small tree or not.