Phisherman wrote:
...My choice is a propane torch or RoundUp--both are kind to concrete and
the environment...




The propane torch is effective against broadleafed weeds, but not
grasses. The growing point of grasses is located below ground, so the
flame doesn't affect it. Excessive heat against concrete or asphalt
could damage it.

Note that it is not necessary to char the plant, only to heat up the
leaves enough to boil the liquid inside. This ruptures the cell wall and
the plant dies. When you apply the flame, the leaves take on a brief
shiny appearance due to the fluids coming out of the surface. It may not
look as if it has died for a few minutes, but be patient. If the plant
is more than 2" high, it may take several heat treatments to fully kill
it. Trying to reduce the plant to charcoal is a waste of fuel and time
(although in the case of really tough plants it may be psychologically
satisfying).

I tried household vinegar a few years ago on broadleafed weeds on a
gravel parking lot. It killed the grasses and broadleaved weeds, but two
weeks later they were there again. The propane torch worked better.