David E. Ross wrote:

As others have said use glyphosate. Roundup is the trade name of the
original and (often) the most expensive version. Follow the
directions for use and safety instructions carefully. The point
about using it effectively is to use it when the plant is growing
strongly so that firstly it is absorbed through the leaves and
secondly it is carried down to the roots through the plant's system.
Some people use it when the plant is dormant thinking when the plant
is weaker it is vulnerable: wrong. Avoid spraying when rain is
coming or before using a sprinkler as if you wash it off before it
is absorbed it won't work, contact in itself does nothing.

I once read that, for vigorous perennial weeds, mix RoundUp slightly
less strong than the label instructions. It does damage the entire
plant not just the roots. By making it a bit weak, you ensure that it
does indeed reach the roots instead of killing the path to the roots.

For any spray or brush-on chemical, I always add liquid soap as a
wetting agent.

This is a good idea, the later versions of Roundup contain a wetting agent.

D