Merlin wrote:
....
If I sprayed an area around a tree with roundup, wouldn't that affect
the tree?

As long as the roots are below grade or heavily barked, no. Roundup is
not a systemic as the active ingredient (glyphosate) is readily bound in
the soil.

Or a bush?

Same thing although if the bush is "droopy" applying it underneath is
more problematical w/o getting it on the foliage.

And if both cases, of course, overspray and misting and bounceback are
issues to be careful of.

Also, how could I control the spray along a 200 ft ditch so that it
was straight and appealing to the eye like I can with a trimmer?

That would be quite difficult w/o a physical border of some sort imo.

I'm all for making my life easier, but I don't want it to look like
hell.

Also, as I said, my arms aren't what they used to be. I was
considering one of the back pack units so the part I'm holding would
be lighter. Is this practical?

Seems like but I've not used one so can't personally comment on how
effectively it might be to accomplish the goal.

At least you don't have the half-mile of cedar windbreak that needs the
weeds taken out of at least a couple of times per year that can't get to
w/ the weedeater owing to branches coming to the ground (which, of
course, is not fixable if one wants an effective windbreak). So, I
still use the scythe. Makes for good exercise if nothing else, I tell
myself...

--