Vinegar can be effective in killing weeds if it's high in acetic acid.
When using vinegar as a weed killer, it's best to apply it directly to the leaves and stems of the weeds on a sunny day. The higher the concentration of acetic acid in the vinegar, the more effective it will be in killing the weeds. Household vinegar typically contains about 5% acetic acid, but for stronger results, you can use horticultural vinegar with a higher acetic acid concentration.
Keep in mind that vinegar may not be as effective on established or deep-rooted weeds, and it might need multiple applications to completely eliminate them. Additionally, be cautious when using vinegar around desirable plants, as it can harm them too.
Click here for instructions for using 20% vinegar in your landscape.
BONUS ARTICLE from Better Homes & Gardens with great info on using 20% vinegar is here.