by Jim Hudgings
Here is the sidewalk spray recipe used by the Sierra Club Youth Corps program in summer 2017, as a good alternative to toxic herbicides:
1 gallon distilled white vinegar
1/2 cup table salt
1/2 teaspoon liquid dish soap
I pour a small amount of vinegar from the jug into my sprayer in order to make room in the jug for salt, then pour the salt into the jug of vinegar and shake it vigorously to dissolve the salt so that it won’t clog my sprayer nozzle. Pour the salted vinegar into the sprayer and add the liquid dish soap. Briefly swirl the sprayer to mix in the soap, but not enough to generate suds. Spray it on the sidewalk, ideally in the morning of a very sunny day.
When finished, I spray plain water for a few seconds to clean the wand and nozzle in order to avoid re-crystallized salt from clogging the nozzle.
[Update: see a similar recommendation here, with different proportions.]