Vinegar - Useful tool in the fight against invasives or just an essential ingredient in salad dressing?

By Ellen Jacquart


I have been intrigued by reports I've heard from people using vinegar against invasive species as an alternative to other herbicides. Always on the lookout for safe, effective ways to kill weeds, I was willing to try it after reading a 2002 report from USDA researchers confirming that vinegar, or acetic acid, is effective at killing some common weed species, including Canada thistle, lamb's-quarters, giant foxtail, velvetleaf and smooth pigweed.

In this study, 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. More information about the USDA study is available online here

I had to try this for myself. This spring I purchased a 24 oz. bottle of BurnOut, a weed and grass killer with 6.25% acetic and ethanoic acid (table vinegar is about 5% acetic acid) for $6.45 at the local farm co-op. A mixture of vinegar and lemon juice, I figured regardless of whether it worked, at least the woods would smell fresh and clean.

Since the USDA report made it clear that perennial weeds are only top killed, I decided to try it against garlic mustard, a biennial. In early April, I sprayed several second year garlic mustard plants that were just starting to bolt. Within an hour, the leaves of the sprayed plants had completed wilted. And yes, there was a very refreshing smell in the air. However, two weeks later I checked the plants and they were flowering. The wilting was apparently a temporary response to the treatment and every plant was able to recover fully and bloom.

Based on this experience, I'm not planning to use vinegar again unless my goal is to deodorize a natural area. If you've had a more positive experience with vinegar - for instance, by using different concentration or timing - please email ejacquart@tnc.org. We'll be happy to post successful vinegar treatment experiences.

Note that the use of a vinegar product for killing weeds, unless the material is specifically labeled as a herbicide, is illegal and a violation of federal pesticide laws. Always read and follow all pesticide label directions.


- Photo of bottle of BurnOut next to garlic mustard plant (photo credit Ellen Jacquart)