Horticultural Vinegar for Weed Control, Part 1

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The advice on horticultural vinegar presented below is republished with permission by Miriam Kritzer Van Zant, President/CEO of Community Conservation Botanical Garden of Southern Illinios. You can reach Miriam and the Botanical Garden at ccbgsi@gmail.com with questions about this recipe and what works in your locality.

This is Part 1 of a 2-part series on using horticultural vinegar. Part 2 gives instructions for making vinegar defoliants and includes new formulas, developed for the acid, wet soils of southern Illinois.

Horticultural vinegar, diluted to 15 to 20 percent acetic acid, is used as an ingredient for making defoliants for controlling weeds, including poison ivy. Horticultural vinegar can also be diluted with water to 6 to 10 percent for cleaning. Horticultural vinegar is usually sold by the gallon at concentrations of 20 to 30 percent. USDA allows the sale of unadulterated vinegar at these concentrations as an inert ingredient. However, once mixed into a defoliant, pesticide licensing regulations affect availability, distribution, and increase costs. Therefore, horticultural vinegar is usually offered as is.

Most defoliant formulas now available on the internet promise great results, and were developed for use in arid regions, such as Texas, California, and Australia, known for well drained soils. University studies of acetic acid-based defoliants have shown mixed results in other locations. These include experiments in Oregon, Pennsylvania, and Maryland.

Community Conservation Botanical Garden of Southern Illinois (CCBGSI) is a 501 (c)(3) charity working to establish a conservation botanical garden and sustainable tourism trail in southern Illinois. CCBGSI emphasizes conservation of local native plant varieties and best organic gardening methods for the region.

CCBGSI has been encouraging experimentation with horticultural vinegar to develop more effective defoliant formulas for the acidic wetland soils of southern Illinois. (The best of these are in Part II.) Experimentation is continuing and may yield better formulas still for variation in altitudes, drainage, soil types and target weeds.

Why Use Horticultural Vinegar for Weed Control?

Acetic acid is biodegradable, so unlikely to build up to damage soils in the manner of acid rain. Acetic acid is a byproduct of bacterial fermentation of sugars and ethanol — it is continuously being produced in all living soils and is a byproduct of the breakdown of all plant and animal tissue. Horticultural vinegar containing defoliants can be used in place of carcinogenic and other agricultural chemicals for controlling weeds that harm wildlife, pets, and all of us.

Glyphosate/Roundup® is considered a probable carcinogen. Other herbicides are often confirmed carcinogens. Recent research on glyphosate in Sweden, acknowledged by the World Health Organization (WHO), has furthered its recognition as a possible carcinogen. Carcinogenic chemicals are not appropriate for use in organic gardens, or around pets, children, cancer survivors and cancer susceptible individuals. Mutagenic carcinogens can compromise the health of wildlife including fish, frogs, butterflies and more.

Systemic herbicides are likely to destroy fungi beneficial to plants, such as those forming mycorrhizal networks that are connected to roots. Bacteria needed by beneficial fungi, or otherwise involved in maintaining soil health, can also be destroyed by systemic pesticides. It takes many years for slow-growing mycorrhizal networks to grow back.

Weed killers are necessary in the battle against invasive species, and to produce enough food for all people. Glyphosate is a natural product, originally found in a soil bacterium. As with all poisons, quantity makes a difference. However, mutagenic and carcinogenic effects are a concern for human health, and the health of natural systems, even with natural products.

Vinegar may not provide the solution for every weed situation, but it is a good start for many and reduces the use of more harmful substances in our shared environment. The decision to use vinegar for weed control promotes thinking on these issues, and builds markets that can lead to even better methods. Used properly, horticultural vinegar-based defoliants work. Hopefully, farmers, gardeners, ecologists battling invasive species, and others who know about these issues, will try this alternative method for weed control with an open mind.

Effectiveness of Horticultural Vinegar Solutions for Weed Control

Horticultural vinegar solutions soften the waxy cuticle that protects leaves. The sun then wilts the leaf. Attached wilted leaves is the most desirable outcome from ecological burns. Wilted attached leaves help to exhaust root stores, as plants frequently try to revive them. As for any defoliant, using vinegar solutions requires more patience, and more applications, than systemic herbicides. This is especially true in wet years like this one.

Weed control in 2017 was made more difficult by spring weather that effectively began in February instead of March or April. People living on higher ground than myself, may not need to spray as often as I have had to this year. If you’re starting to use horticultural vinegar-based defoliants later in the season during 2017, there’s no doubt that less frequent and lighter rain in late summer has caused the water table to drop faster after rain, than in April.

This should help with better overall results. However, plants have had additional time to establish food stores in their roots, so may still require multiple repeat applications. If one stops treating the problem as needed, especially in extreme wet conditions, weeds that appeared completely wilted may still recover. If kept up, less and less defoliant is needed as the season progresses. Some plants stop re-sprouting sooner than others.

Some solutions of horticultural vinegar have been said to work better when plants begin to grow again with the next rain after application. In my experience, that can be the case, though not always. In southern Illinois soils, rapid follow up, through re-treatment for newly opened leaves on recently treated plants, has given good results. Poison ivy has cuticles that seem thickest on some leaves when they have barely emerged. For these leaves, cuticles seem to become a little thinner as the leaf grows.

So, some young leaves wilt easily, as soon as they appear, while others only wilt when leaves are a little larger. It may also be that after treatment, some new leaves receive thicker cuticles then earlier leaves had. This is hard to predict. You can expect different leaves to have different wilt rates, even at the same stages of growth. Your eyes will tell you which leaves wilted and which need re-treatment.

To counter variation in effectiveness of vinegar defoliants and leaf responses to them, check for at least three days after treatment, as some sprayed leaf buds continue to open and develop. Follow that up with weekly checks until plants appear to have no unwilted leaves. Continue to check at least every two weeks throughout the growing season, if possible. Spray new growth as soon as you can. Poison ivy roots with stored food remaining may send up new shoots nearby, even after treated shoots are completely wilted. In some cases, there will be a delay of several weeks before new shoots appear.

Other Ways to Control Weeds

Fire is effective for wilting leaves but dangerous, especially near homes and wooden structures, more so in untrained hands, and without proper safety equipment. Fire is unsuited to non-fire resistant trees such as American elms. Vinegar gives similar results more safely.

Steam is effective for wilting leaves, however, very slow going with a home steamer as it is necessary to stand in each spot for several minutes and inch along. Plus steamers use electricity and have to be plugged in. Works well on grasses and many weeds but poison ivy only wiggled like it was being tickled by the steam. Super-heated steamers are permanently mounted on truck beds for use for road-side weeding in some counties in California and in Australia. Not practical and too costly in time and money for use by the weekend gardener. It may be that super-heated large steamers will work in southern Illinois but it will cost a bit to find out.

Black plastic is useful over cut down woody and tall weeds. Cover stumps and persistent roots with black plastic and weight down the plastic with stones or bricks. This is about light deprivation so be sure light is really keep out. Leave the plastic in place for several weeks. Use the best vinegar solution for your area to catch any re-sprouts after that. Be sure to reuse or recycle leftover plastic sheets. There are drawbacks. Most plastic can only be recycled so many times before it won’t melt down for reuse anymore. There may also be some nasty additives to make it persistent and dark. Plastic used outdoors soon gets holes that allow light to get in.

Corn gluten meal is supposed to prevent weeds from emerging. Can only be used when planting plants, or prior to planting seeds. Researchers at Iowa State University reported good results, Oregon State University (OSU) researchers could not get the same. Southern Illinois shares rainfall patterns with Corvallis where OSU is located though the southern Illinois water table is usually higher. Most southern Illinois soils have considerable clay, like those in Iowa and unlike most soils in Oregon. However, southern Illinois soils tend to be wetter than Iowa soils. I’ve never tried corn gluten in the garden. It’s not particularly cheap to use and probably more cost effective with drier soils.

CCBGSI is asking you to experiment to find the best formulas for your property, conditions and target weeds, and to share that information with the rest of us. Please send your best effective formulas to ccbgsi@gmail.com. To join the CCBGSI mailing list, donate to CCBGSI, or for information on obtaining horticultural vinegar via donation to benefit CCBGSI, please send an inquiry to the e-mail address above.


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