In a spray bottle mix 1 litre of white vinegar, 1/4 cup of salt and (this is optional) a teaspoon of dish washing liquid. There's a note below about using dish washing liquid in the mix.
Give it a bit of a shake until the salt has dissolved, then it's ready to use. The weed spray works best on a sunny day.
I didn't take a "before" photo - but these photos give you an idea of the results.
This is 2 hours after spraying. It's leaves are already beginning to wilt.
Two days after spraying
Two weeks and it's brown, dry and dead.
Note: The dish washing liquid makes the spray "stick" to the weeds. I've tried it with and without, but there doesn't seem to be much difference in performance. If you do use dish washing liquid add it to the spray bottle last. The first time I made this put the liquid in before the vinegar - bubbles came up out of the spray bottle and ran down the sides - oops!