WASHINGTON STATE UNIVERSITY EXTENSION FACT SHEET • FS161E
Acetic acid is one of the simplest organic acids. Here,
“organic” means a compound having carbon molecules.
It is a naturally occurring substance found in all plants,
animals, and humans in tiny amounts.
Acetic acid is one of the few chemicals with two common
names. Both depend upon its concentration. “Vinegar”
means concentrations up to 8%. “Acetic acid” means
concentrations higher than 8%. When the concentration
is low enough to be called vinegar, it is a food product.
Most household (food) vinegar is sold at a 5% concentra-
tion. The U.S. Food and Drug Agency (FDA) regulates food
When the concentration is high enough to be called acetic
acid, and it is used to kill weeds, it is a pesticide. The U.S.
Environmental Protection Agency (EPA) regulates pesti-
cides. When the concentration is low enough to be called
vinegar, but is sold as an herbicide, the Washington State
Dept. of Agriculture regulates it as a pesticide.
This chemical is made through bacterial fermentation (for
example, turning apple cider into vinegar) or industrial
reactions (for example, turning methanol into acetic acid).
If you are looking for a product that is “certied organic,”
things get a bit more complicated. Here, “certied organic”
means a substance or product that has been certied
through the USDA National Organic Program’s (NOP)
third-party agents. Examples of nearby agents include: the
Organic Materials Review Institute (OMRI), Oregon Tilth
Certied Organic (OTCO), and the WSDA Organic Food
Program (OFP). Organic certication rules are partly built
on the source of starting material. Take organically pro-
duced apple cider for example. If it is made into vinegar
using natural processes, then it is acceptable under organic
standards. If it is made into vinegar using synthetic pro-
cesses, it is not acceptable. If methanol is used to make
acetic acid, which is then diluted to 8%, that vinegar is not
acceptable under organic standards.
How it works as a pesticide
Acetic acid is applied as a liquid spray or drench to weeds
after they emerge from the soil. It is a contact herbicide,
meaning it only affects plant tissue it touches. The acid
breaks up cell membranes and makes them leak, causing
the plant to dry out and die. Depending on plant age, air
temperature, humidity, and direct sunlight levels, this may
take from a few hours to several days. The drying effect is
not limited to just certain plants; any new plant tissue can
be affected. Avoid getting drops of spray onto plants you
do not want damaged.
Young seedlings and new growth have a thinner leaf cuti-
cle than older plants or woody parts, making it easier for
acetic acid to break down cell membranes. For example,
in one study acetic acid sprayed at 5%–20% concentra-
tion killed 80%–100% of weed seedlings that were from 3
inches–9 inches tall. However, when 10% acetic acid was
sprayed on mature blackberry plants, only 5% of leaves
were burned back. Thick, waxy cuticles and woody plant
tissue are more resistant to liquid entering, thus harder
to kill. To overcome this, trim perennial weeds so they
regrow tender new growth. Follow this with a spray appli-
cation to the new growth to deplete the weed’s energy
stores. Many cycles of trim-and-spray are likely needed to
effectively treat stubborn perennial weeds such as Canada
thistle (Figure 1).
Acetic acid is sometimes mixed with citric or other acids.
It can also be listed as an inert ingredient on some herbi-
cide labels. The point to remember with acetic acid is that
high concentrations are more effective on woody perennial
weeds, while low concentrations will work effectively only
on very young weed seedlings.
This fact sheet is part of the WSU Extension Home Garden Series.
WSU Extension Pesticide Ingredient
factsheets describe basic traits of active
ingredients found in WSDA-registered
Only apply pesticides to crops or sites listed on the label.
Always store pesticides out of the reach of children and
pets, preferably in locked cabinets. Keep pesticides in their
original containers so instructions on personal protective
gear and other precautions are easy to nd. Dispose of pes-
ticides by contacting your local Hazardous Waste facility.
Eye damage or irritation is possible, so it is important to
wear goggles or face masks when applying products con-
taining acetic acid. Sprayers with tin, aluminum, or iron
parts exposed to the acetic acid solution will be damaged.
So will any lawn furniture touched by the spray.
The Pesticide Information Center Online (PICOL) database
lists all of the registered pesticides in Washington and
Oregon. This source is free and can be used to identify
products with specic active ingredients. The PICOL
database can be accessed at http://cru66.cahe.wsu.edu/
The National Pesticide Information Center (NPIC) (through
an agreement with the EPA) provides objective, science-
based information on pesticides. The fact sheets provid-
ed have information on ingredient toxicity and known
environmental effects. The NPIC site can be found at
The EPA has a wide range of technical information about
pesticides, including fact sheets, which can be accessed
The USDA National Organic Program (NOP). http://www.
The U.S. Environmental Protection Agency (EPA) regu-
lations.gov website. Acetic Acid and Salts Summary
Document Registration Review: Initial Docket March 27,
2007(see ID: 2008-0016-0003). http://www.regulations.
The Government Publishing Company Code of Federal
Regulations. Crop Pest, Weed and Disease Management
Practice Standard 7CFR1.205.206(e). http://www.ecfr.
Figure 1. Treated Canada thistle in raspberry bed. Treated
area (below the red line) shows inconsistent death of thistle
leaves. (Photo by Timothy Miller, WSU)
By Catherine Daniels, Pesticide Coordinator, Washington State Pest Management Resource Service, WSU Puyallup Research and Extension Center;
Timothy Miller, Weed Scientist, WSU Mount Vernon Northwestern Washington Research and Extension Center.
Header image: Molecular structure of acetic acid. Chemical Abstract Service (CAS) Number 64-19-7.
Use pesticides with care. Apply them only to plants, animals, or sites as listed on the label. When mixing and applying pesticides, follow all label
precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing,
remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.
Copyright 2015 Washington State University
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Issued by Washington State University Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Extension
programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, sex, religion, age, color, creed, and
national or ethnic origin; physical, mental, or sensory disability; marital status or sexual orientation; and status as a Vietnam-era or disabled veteran. Evidence
of noncompliance may be reported through your local WSU Extension ofce. Trade names have been used to simplify information; no endorsement is
intended. Published January 2015.
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