Vinegar as a 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
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
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.
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.
Acetic Acid, or more commonly known as vinegar has been proven to be an effective herbicide when used at moderate concentrations. A
20% solution of vinegar tested against leading chemical herbicides on various weeds and grasses reveals just how effective vinegar is as a
herbicide. University studies document that a 20% vinegar solution can directly compete with the common chemical herbicide Roundup
(glyphosate). The vinegar solution actually performs better, is cheaper, and is drastically safer to use than a chemical herbicide!
The word vinegar comes from vinegre, coined from two Latin words vinum meaning wine and acer meaning sour. There are a number of
historical references about the use of vinegar as a preservative, condiment, beauty aid, cleaning agent and medicine.
Vinegar can be produced naturally by decomposition of plant products under anaerobic conditions. Acetic acid, commonly called ethanoic
acid, with a chemical formula CH3COOH, is formed by the fermentation of alcohol. Vinegar of about 5% acetic acid concentration is
prepared from wine (grapes), cider (apples), or malt (grain). The biological process of vinegar manufacture involves conversion of sugars
into alcohol and carbon-dioxide through fermentation. By an oxidative process, the alcohol in presence of certain bacteria reacts with air to
form vinegar. Concentrated acetic acid as used in industry is prepared by several synthetic processes, such as the reaction of methyl alcohol
and carbon monoxide (CO) in the presence of a catalyst, or the oxidation of acetaldehyde or petroleum. This synthetic process is not
acceptable for agricultural use by the organic community. Acetic acid concentration of vinegar derived from plant sources can be increased
from 5 % to 15% via distillation and to 30% via freeze evaporation or other processes. The organic community approves of these processes
for agricultural use.
Environmental fate of acetic acid:Acetic acid readily degrades in water and shows little potential for bioaccumulation. It is biodegradable
(MITI Report 1984, Ministry of International Trade and Industry, Tokyo). In an experiment conducted at Swedish Agricultural University it
was found that addition of 24 % vinegar to a peat soil decreased the pH of the soil from 7.3 to 5.6. However, after 48 hours the pH values
of the soil returned to 7.0-7.5. (David Hansson, personal communication)
Research Results from BARC
Greenhouse and field research have been conducted at Beltsville, Maryland, to determine the efficacy of vinegar for controlling weeds. The
results indicate that vinegar can kill several important weed species at several growth stages. Vinegar at 10, 15 or 20 % acetic acid
concentration provided 80-100 percent kill of selected annual weeds, including giant foxtail up to 3 inches in height, common lambsquarters
up to 5 inches, smooth pigweed up to 6 inches, and velvetleaf up to 9 inches. Control of annual weeds with vinegar at the 5 % acetic acid
concentration was variable. Canada thistle shoots were highly susceptible with 100 percent kill by 5 % vinegar.
Spot spraying at the base of corn rows in the field indicated that corn plants were not affected by vinegar, and 90-100 percent
control of weeds was obtained.
Potential applications for using vinegar for controlling weeds:
An inexpensive, environmentally safe herbicide for spot treatment on organic farms.
Control of unwanted vegetation along roadsides and range lands
Control of weeds by homeowners around yards, brick walls and patios
Weed control in cracks in pavements (It is registered for this use in Sweden, David Hansson, Personal communication)
Vinegar proving useful in weed battle
By DAVID DICKEY
American News Writer
Many people are familiar with the wide variety of uses for vinegar. It's often used as a spice for salads and fine dressings, a disinfectant and
even a stain remover in some cases. With so many uses, it should come as no surprise that vinegar is quickly becoming a popular product in
the war on weeds.
"I started using it three years ago," said Gary Cwach, a farmer in Yankton. "I was having a lot of trouble with Canada thistle, and nothing I
tried worked. I finally tried using vinegar, and it worked well. Using it and getting the calcium level in the soil where it belongs have been the
Cwach said vinegar is not only cheaper than chemical herbicides, it's also a safer and more natural way to get rid of weeds.
Cwach dispenses the vinegar by putting it into a 15-gallon spray tank that he attaches to an all-terrain vehicle. The vinegar, which is fully
biodegradeable, is released through a 14-foot-long boom. He said he usually makes two passes over areas in need of spraying. On
average, he uses about five gallons of vinegar an acre.
"It's been effective for me, and it's something worth taking a look at," Cwach added.
Norbert Haverkamp, said he has been selling vinegar as a weed killer for the last 15 years. He said it has been popular with organic farmers
and farmers who have become wary of using chemical sprays.
"Too many people are having bad reactions to the chemicals they've used," Haverkamp said. "Because of that, more people are getting
interested in safe alternatives. I think you'll see more farms using vinegar as time goes on."
Finding information about vinegar is fairly easy to do, according Haverkamp. However, he said there is a lack of hard, scientific facts
available about vinegar and its use as a method of weed control. That may change, thanks to a study being conducted by the Agricultural
Research Service in Beltsville, Md., the chief scientific research agency of the
U.S. Department of Agriculture.
ARS researchers Jay Radhakrishnan, John R. Teasdale and Ben Coffman began a scientific study of vinegar as a weed killer about two
years ago. The study is credited as being the first of its kind.
So far, the researchers have tested vinegar on the most common weeds, including common lamb's quarters, giant foxtail, velvetleaf, smooth
pigweed and Canada thistle. The tests have been done in a greenhouse and in the field.
The weeds' leaves were sprayed uniformly with various solutions of vinegar made from fruits and grains, and the researchers determined that
5- and 10-percent concentrations killed the weeds during their first two weeks of life. A bottle of household vinegar is about a 5-percent
concentration. 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.
Canada thistle, which is considered one of the most tenacious weeds in the world, proved to be the most susceptible to vinegar. The
5-percent concentration had a 100-percent kill rate of the perennial's top growth. The 20-percent concentration had the same effect in a
two-hour time frame.
Spot spraying of cornfields with a 20-percent concentration of vinegar killed 80 to 100 percent of the weeds without harming the
corn, but the three scientists said there's still a need for more research.
Coffman said studies are currently being done to test vinegar's effectiveness in killing perennials like Canada thistle by soaking the ground
containing the weeds. By doing so, Coffman said the weed's root system, which contains a high level of nutrients, can be attacked directly.
"One of the positives of using vinegar is that it works on annual plants, and it does so with one application," Coffman said. "With perennials, it
takes several applications and you have to get to the root system."
Coffman said the study is still in its infancy, but data generated so far has been positive, which is good news to those with weed problems.
Among this group are organic farmers, who must adhere to strict guidelines when it comes to killing weeds.
"We're still early in the stages of the study, but it is showing a great deal of promise," Coffman said.
Lonny Mikkonen of Frederick said his use of vinegar to kill weeds has been limited, and he is eager to see what the ARS' studies conclude.
Mikkonen, who has been a certified organic farmer since 1989, said he currently uses methods like tilling and rotation to control weeds. But
he does have a large drum filled with vinegar should the need for spraying arise.
"I use (vinegar) for a few problems that I can't solve through tillage and rotation," Mikkonen said.