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I am trying to find an organic solution to spraying weeds in the vegetable garden, such as morning glory. Would a mix of vinegar and lemon juice spread to the roots of the vegetables also, or could it be used? If so, do you have any information on proportions for the mix?

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A

Sadly there are very few good organic herbicides for perennial, persistent and quite annoying weeds like field bind weed. Even our best chemical herbicides will not completely control this aggressive invader.

However, there are some organic herbicides on the market that have the “burn back” characteristics of the chemical glyphosate (trade name Round-up and others). These include organic herbicides like AllDown (citric acid (5%), garlic (0.2%), acetic acid, yucca extracts, water (94.8%)), Matran 2 (clove oil (33.7%) and acetic acid), Xpress (thyme oil (10.4%), clove oil (10.1%), acetic acid, molasses, water (79.5%)), or Nature’s Avenger (natural citrus oil based non-selective herbicide). Each contains various combinations of natural oils or acids. As you can see some of these say that they have acetic acid (vinegar) in them but say nothing about the strength of that vinegar or what percent of the solutions are vinegar or water. Most of the organic chemicals (trade names) are available on the internet.

In some work done by the Sustainable Agricultural Systems Laboratory (part of the US Dept of Agriculture) on using vinegar as a herbicide, they showed 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 (most products sold in grocery stores contain 5% acetic acid) was variable. Canada thistle shoots were highly susceptible with 100 percent kill by 5% vinegar, however, there was re-growth from roots. Sadly, established perennial weeds (like bindweed) usually will not be killed by vinegar. Even under repeated applications to the growing tissue, they still came back.

One needs to be very careful with concentrated acetic acid as it does burn and can injure the user if you get it on your skin or in your eyes or throat (inhale it). So watch out if you decide to use it. You can try and make your own but unless you get the concentration of the acids up to high levels, they are not that effective.

You also need to remember that these are contact herbicides and will damage any green tissue they come into contact with. So if you are using them in the vegetable garden, they will “burn back” the vegetable as well as the weeds. So be extra careful.

Hope this helps.

Posted on 4 Jun 2008

Dan Drost
Vegetable Specialist

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