Vinegar is a common ingredient in dressings for garden-fresh salads. Now it appears that you can use vinegar in the garden as well. Studies at Cornell University have shown that concentrations of 25 percent acetic acid (vinegar) are effective at killing a wide range of annual and perennial weeds. Tests on weeds such a lambsquarters, crabgrass, pigweed, dandelions, and Canada thistle showed that a 25 percent vinegar solution killed 80-100 percent of these weeds.
Since regular vinegar contains only 5 percent acetic acid, you'll have to rely on commercial products, such as Burnout, to dose your weeds. Tenacious perennial weeds such as dandelions, will need repeated applications to kill them. Vinegar kills any plant that it comes in contact with, so apply it only to the weeds you want killed. For that reason, it's most safely used on weeds in walkways and patios.
For more information on using vinegar as an herbicide, go to this USDA Web page: www.barc.usda.gov/anri/sasl/vinegar.html.