Vinegar as an Organic Weed Killer

by Patricia Diaz, from the July 2002 Newsletter

A recent Lewiston Tribune article has sparked a lot of local interest in the promise of vinegar as an herbicide. Yes, even regular household vinegar works! Since the number of organic products available for killing unwanted weeds is extremely limited, the vinegar solution is a most welcome addition.

Vinegar has long been used in cooking, cleaning, and for a host of other applications (haven't you ever gotten that "forward" on the internet?) and its potential use as an herbicide is exciting. Vinegar can be produced naturally by decomposing plant products under anaerobic conditions. Household vinegar is usually made from wine (grapes), cider (apples), or malt (grain). The sugars in these plant products are converted into alcohol and carbon dioxide through fermentation. This oxidative process forms vinegar.

Regular household vinegar is a 5% acetic acid concentration. While this works on some weeds, a greater concentration is needed for other or more mature weeds. By distilling, a 15% concentration can be obtained, and a 30% concentration can be obtained by freeze evaporation. These concentrated acetic acids, if they are derived from plant sources and not from chemicals, are acceptable for agricultural use by the organic community.

Acetic acid readily degrades in water (so I wouldn't spray right before an expected rainstorm) and doesn't bioaccumulate. Vinegar will decrease the pH of the soil somewhat, but within 48 hours the pH balance is back to its original state. It is also a biodegradable product.

Currently, research is being conducted at Beltsville, Maryland, at the USDA site to determine the efficacy of vinegar for controlling weeds. I conversed via email with John R. Teasdale in Beltsville, who very kindly sent me the URL of a Web site where we can all keep abreast of the latest developments in this field: http://www.barc.usda.gov/anri/sasl/vinegar.html.

I also talked with local Cooperative Extension specialists at both the U of I and WSU to determine if there was any research being conducted locally into this exciting development. Carol Miles, from WSU Vancouver, said that WSU is unable to recommend something as an herbicide unless it has herbicide information on the label–which vinegar does not–plus she hadn't seen this research yet. She did, however, recommend Scythe, an all-organic herbicide, as something organic gardeners could use, as well as using plastic with mulch (irrigating under the plastic). Tim Prather, from UI, is conversant with this new research and recommended that whoever starts using vinegar in an organic garden needs to be aware of the source of the vinegar. Otherwise, the organic certification could be compromised. He said that research is being conducted in California using vinegar and he's the one who recommended contacting John Teasdale, a long-time researcher in sustainable issues. He also said that you could use a surfactant, such as Ivory soap, to increase coverage ability of vinegar.

The research conducted so far using vinegar shows that vinegar can kill several weed species at different growth stages. Using 10, 15 or 20% acetic acid concentrations, field researchers had an 80-100% kill rate of selected weeds, including giant foxtail up to 3" tall, common lambsquarter up to 5 inches, smooth pigweed up to 6 inches, and velvetleaf up to 9 inches. Using household vinegar (5%) produced variable results but seemed to be the most effective on Canada thistle where a 100% kill rate of the top growth was achieved. Re-growth from the roots, however, continued. Tim Prather, from UI, stated that you could achieve better results by spraying very small plants, 2-6 leaves. Continue spraying at two-week intervals. He's found that the maximum stage for the best kill-rate is the 4-leaf stage.

The organic vinegar that these researchers used was from Burns-Philip Food Inc. and Heinz USA (concentrations ranging from 5-30%), as well as from Knouse Foods (14% concentration).

Of course I couldn't write this without trying it myself, so out I went with my spray bottle and white distilled vinegar (probably not organic but I was clear out in a field spraying and marking the weeds). I sprayed the weeds in late morning (for no particular reason, that's just when I did it) and checked late that afternoon. And I had some really pleasant surprises! I sprayed two sizes of Canada thistle (11" and 4") and the vinegar killed all the top growth; I sprayed Dalmatian toadflax and bracken fern, both noxious weeds out our way, and the vinegar didn't faze them in the least. I also sprayed both broadleaf plantain and English plantain, sizes 2" and 5" and the vinegar killed them dead. Our little schnauzer was allergic to English plantain and when I think of all the hours I spent digging those up when I could have been leisurely spraying vinegar, oh my. . . I don't have any yellow star thistle close by to test, but wouldn't it be wonderful if vinegar killed that too?

Another bit of research conducted was done on cornfields: spot spraying with 20% concentration killed 80-100% of weeds without harming the corn. This is an area where the scientists say they are actively continuing to do more research.

I talked with Kirk Arrasmith of Central Stores at WSU and they do have a couple of sizes (2.5 liter and 500 ml) of the higher concentrations of acetic acid. These aren't organic, however, but made for industrial use. But if you're interested in killing weeds around the driveway, sidewalk, etc. and just don't like chemicals, these will work fine. Just go to Central Stores on Grimes Way, pay for your product, get your receipt, and then proceed to Chemical Stores. They'll give you directions at Central Stores. Val, at WSU's Food Science and Human Nutrition, was very helpful in giving me contact numbers for the above-mentioned food companies: Knouse, at 717-677-8181; and Burn-Philip Foods at 800-443-1067. I would suspect that as this research progresses the availability of the higher concentrations of organic acetic acid will increase. I emailed Heinz USA about obtaining the higher concentrations of acetic acid but at press time I hadn't heard from anyone.

Pat Diaz lives on 6 acres in the woods near Dworshak Reservoir with her husband, Tom, and newly adopted schnauzer, Gunther. With all the rain and then the sun, the potatoes, tomatoes, and squashes are going nuts!

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