Round Up is so expensive and icky that I decided that there had to be a non-toxic way to kill weeds that my dog could even lick up.
There was! I found it on-line at http://www.thriftyfun.com/tf001029.tip.html
Here's what I do: Mix 1/3 cup salt into 1/2 cup very hot water. Stir well and dissolve salt completely. Add 2 cups of white vinegar. Pour into spray bottle and squirt onto weeds.
It also works best on hot sunny days when there will be no rain for a few days after you spray them.
The horsetail in the yard is the worst and almost impossible to kill. So first, I cut them off with the weed wacker or clippers and then sprayed the open ends with my new cocktail of death.
And it worked! In a couple of days, all the weeds I test sprayed were dead!
those are my dead horsetail (Round Up wouldn't even dull their green color)
the other dead weeds in our steps
*The only warning is not to do this anywhere near things you don't want to die or grow plants again. (like your grass or flowerbeds) Salt renders your soil infertile. But it's great for walks and driveways!