Does Vinegar Kill Musk Thistle?

Musk thistle (Carduus nutans) is an invasive biennial or winter annual that grows in U.S. Department of Agriculture plant hardiness zones 3 through 11. This noxious weed spreads via seeds and can inhibit the growth of desirable plants such as pasture for grazing livestock. Also known as nodding thistle, the plant's typically solitary flowerhead nods on its slender stem. The flowers are colorful and pom-pom shaped, but beneath the flower lie sharp spines, which also appear on the foliage. Herbicides can control musk thistle but often contain harsh chemicals. Instead, consider using a less toxic homemade herbicide containing vinegar.

Musk Thistle Description

Musk thistle can adapt to a wide array of growing conditions and often grows in open disturbed sites, pastures, along roads, in annual grasslands and in waste areas. One single musk thistle can produce 20,000 seeds, which may stay viable in the soil for several years. These seeds are dispersed via the wind and most only travel about 130 feet away from the parent musk thistle. The key to eradicating musk thistle is to do so before the plant produces seed so apply the herbicide before it blooms.

Vinegar as a Weed Killer

The acetic acid in vinegar is what kills plants by dissolving the cell membrane in plant tissue. This causes the plant to dry out or burn. Five percent acetic acid is the common vinegar strength found in homes. This strength will merely burn the above ground portion of musk thistle but does nothing to the roots. A higher acetic acid strength is need to effectively kill musk thistle. The Oregon State Department of Agriculture website suggests using vinegar with a 10 to 20 percent acetic acid, which will provide 80 to 100 percent control over weeds.

Applying Vinegar to Musk Thistle

Several different weed killer recipes containing vinegar are available, and most will do the intended job as long as you use the right percentage of acetic acid. The University of Washington Botanic Gardens website suggests two recipes containing vinegar that can help control weeds. The first requires mixing 1 quart of vinegar with 4 ounces of lemon juice. The second recipe calls for 1 tablespoon of vinegar, 1 tablespoon of gin and 1 teaspoon of liquid dish soap mixed in 1 quart of water. No matter which homemade herbicide recipe you choose, apply it as a foliar spray to the musk thistle. You should use the homemade vinegar herbicide within 24 hours after mixing the ingredients together. Keep in mind that vinegar works best as a weed killer when used on a sunny day.

Considerations, Precautions and Warnings

Vinegar with an acetic acid higher than 5-percent can cause skin, nose, eyes and throat irritation. Wearing protective eyewear, dust mask, rubber gloves, long-sleeve shirt and pants will help protect against possible hazards caused by the vinegar. Avoiding spraying in a breeze. Furthermore, the vinegar herbicide will damage or kill any plant it encounters. Covering desirable plants growing nearby the musk thistle with a plastic tarp will protect them from the herbicide. The vinegar weed killer will prevent growth for 3 to 5 days after the applications, according to the University of Washington Botanic Gardens website, so avoid replanting in that area during this period.

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