Acetic acid, also known as vinegar, is used in products for weed control. Many people choose it because it is natural. However, acetic acid can damage skin and eyes, especially at concentrations commonly found in weed killers.
What is the difference between acetic acid, vinegar, and horticultural vinegar?
You may know acetic acid best as vinegar. Vinegar is a solution of acetic acid in water. Acetic acid is a naturally occurring substance that is found in all living things. It is formed during fermentation. Acetic acid can also be made industrially. It is used in many industrial processes, including the manufacture of dyes, plastics, some drugs, and other industrial chemicals. It is also used in textile printing.
Household vinegar such as distilled white vinegar used for cleaning or cooking generally contains 4-6% acetic acid, which is diluted in water. Higher strength acetic acid solutions are sold for other purposes. Horticultural vinegar typically refers to a concentrated solution of 20% or more acetic acid. It is sold to kill weeds. You may find even higher concentrations of acetic acid sold in stores or online.
Are there health risks of using vinegar/acetic acid?
Acetic acid is irritating to the eyes and skin. At concentrations above those usually found in household vinegar, it can be extremely irritating or corrosive. Acetic acid can permanently damage the corneas if it gets into your eyes. It can burn skin and the tissues of your mouth and throat if you accidentally swallow it. People have had irritation in their nose, throat, and in their lungs if they breathed in enough of the vapor.
Never leave any pesticide unattended around children or pets. Never leave any pesticide in an unlabeled container. "Natural" does not mean "safe!" Remember, the dose makes the poison. The higher the concentration of acetic acid, the greater the risk.
How does vinegar/acetic acid kill weeds?
Acetic acid is a non-selective contact herbicide. It must touch the foliage of the plant in order to work. It does not damage tissue it does not touch. It does not travel throughout the plant. Acetic acid breaks open cell walls and causes cell death. The plants die by drying out.
Acetic acid breaks down rapidly in the environment. It does not leave a residue.
Acetic acid readily turns into a vapor. Like other chemicals, warmer temperatures increase volatilization, or turning into a vapor. The vapor can irritate the nose, throat, and lungs if breathed in. Prolonged exposure to high concentrations of the vapor can cause fluid buildup in the lungs.
What sort of pesticide/herbicide products contain vinegar/acetic acid?
Products containing vinegar/acetic acid that have been registered by the United States Environmental Protection Agency (U.S. EPA) as pesticides/herbicides will have a signal word and an EPA registration number on their packaging. Label information includes where and how to use the product, what precautions to take, personal protective gear to wear while using the product, and first aid instructions in case something goes wrong.
Products registered to be used as herbicides have high concentrations of acetic acid, typically 20% or more. All registered herbicides containing acetic acid have a signal word of DANGER because of the high concentrations and high toxicity. Specifically, it is because of the risks of the acid to the eyes and skin. Low concentrations of acetic acid are used in insect lures.
Acetic acid is available commercially for many purposes. Consider purchasing a product registered as a pesticide if you plan to use acetic acid for weed control. Doing so means you will have directions for use as an herbicide and information on precautions you can take to keep risks low. Products that do not have an EPA registration number and signal word are not registered to be used as herbicides and may not have appropriate safety or precautionary information for that use. Look for an EPA Registration Number and a signal word to ensure you are purchasing a registered product.
How can I reduce the risks when using vinegar/acetic acid?
- Any time you use a pesticide, always read and follow all label instructions. The label is the law.
- If the label specifies personal protective equipment, you must use that equipment.
- Wear long sleeves, long pants, shoes, socks, and gloves at a minimum whenever using any pesticide.
- Consider wearing protective eye wear and chemical resistant gloves when mixing, diluting, or applying vinegar as an herbicide because of its acidic and corrosive nature. The label instructions may require their use.
- Keep everyone else away from the treatment area until dry.
- Keep all pesticides away from children and pets. Remember that horticultural vinegar can badly damage your eyes or blind you!
- Consider integrated pest management strategies that do not use chemicals to control weeds.
For more information about pesticides and pesticide safety, visit the National Pesticide Information Center (NPIC) website at npic.orst.edu.
[Originally featured in the Summer 2024 edition of the Home and Garden Pest Newsletter]