If fighting weeds in your garden has you in a pickle, you’ll be interested in a USDA research report about using acetic acid (vinegar) as an herbicide.
USDA researchers confirmed that acetic acid is effective at killing some common weed species, including Canada thistle, lamb’s-quarters, giant foxtail, velvetleaf and smooth pigweed.
Weeds were hand-sprayed with various solutions of vinegar, uniformly coating the leaves. The researchers found that 5- and 10-percent concentrations killed the weeds during the first two weeks after emergence from the soil. Older plants required higher concentrations of vinegar to kill them. At the higher concentrations, vinegar had an 85- to 100-percent kill rate at all growth stages. However, perennial weeds, such as Canada thistle, were only temporarily knocked back; the roots survived to sprout new shoots.
Even though vinegar is an acid, it breaks down quickly in the soil and, therefore, is not likely to accumulate enough to affect soil pH for more than a few days.
Vinegar causes a rapid burn to plant tissue of susceptible species, so unintended injury is quite likely without knowing more information. Further studies are needed to know whether other crop plants and ornamentals can tolerate the vinegar.
Ordinary household vinegar is about a 5-percent concentration. Stronger solutions that are labeled for use as herbicides are now available from some retailers, you can check the OMRI product database for current products. https://www.omri.org
Note that vinegar with acetic acid concentrations greater than 5 percent may be hazardous and should be handled with appropriate precautions. Vinegar solutions of 11-percent or greater strength can cause skin burns and eye injury. Always read and follow all pesticide label directions.
More information about the USDA study is available online at http://www.ars.usda.gov/is/pr/2002/020515.htm.
