Pure vinegar, such as distilled white vinegar, has an extremely high acidity level and affects plants and weeds in different ways. When used in its pure form, the vinegar acts as an effective killer against weeds and other pest-like plants.
Apply the vinegar directly onto the weeds and any other pest plants, including grass. For unwanted trees, apply a thin layer of rock salt to the roots of the tree first and then coat with vinegar. The combination kills the tree roots, which keeps it from growing.
When you use the vinegar to kill weeds, continue checking the area for several weeks after the initial application. Apply more vinegar, as needed to fully kill the weeds. The weeds may continue to grow after the first application.
According to a study done by the USDA, a vinegar solution was an effective killer against weeds, including foxtail, pigweed and lambsquarters.