Originally written by Gared Shaffer, former SDSU Extension Weeds Field Specialist.
Gardeners always hope to have weed-free gardens. Many homeowners across South Dakota do not want to use inorganic or synthetic herbicides due to their potential health impacts. There may be a need of safer options for weed control in gardens. It is often thought that because herbicides are organic they are safe. This is mostly true due to the quick, natural breakdown of organic herbicides in the environment compared to some inorganic herbicides, which can have residual life in the soil or plant. Even organic herbicides, when applied in high concentrations can potentially pose an acute risk to human health, however, a chronic risk is rarely observed. Every organic herbicide would fall under the title of non-selective, which means it will kill or suppress all plant growth that it comes in contact with. Organic herbicides can be a useful tool when combined with other means of weed control.
Recent Research
Recent research showed that acetic acid is a valuable option to control weeds. Acetic acid is not selective and will damage sensitive plants. Therefore, it is recommended to use only on or near undesirable plants. It was found that using acetic acid in combination with a surfactant can produce 90% control of grasses and broadleaf weeds. Best results were seen with the use of 6.1% acetic acid + 15.4% surfactant followed by 4.2% acetic acid + 8.3% surfactant. Increasing acidic acid to 20% with no surfactant decreased weed control when compared to the treatments with added surfactant.1
Organic Herbicide Considerations
Application
To improve the effects of organic herbicides, consider performing a thorough spray coverage even to the point of running off plant leaf surface.
Other considerations would be to use the highest label rate allowed of surfactant/adjuvant and treat weeds when they are four inches or less in height or at growth stages between two to four leaves.
University research has found that when applying organic herbicides, “lower concentrations at high spray volumes (i.e. 10% concentration in 70 gallons per-acre) appear to be more effective than high concentrations at low spray volumes (i.e. 20% concentration in 35 gallons per-acre)”.2
Active Ingredients
Organic herbicides use one or more of the following active ingredients:
- Acetic Acid
- Citric Acid
- d-limonene (Citrus Oil)
- Clove Oil or Clove Leaf Oil
- Cinnamon Oil
- Lemon grass Oil
- Eugenol
- 2-Phenethyl Propionate
- Sodium Lauryl Sulfate
- Ammonium Nonanoate
- Pelargonic Acid+Fatty Acids
| Active Ingredient (AI) | Product Name |
|---|---|
| Acetic Acid | Vinagreen, Weed Pharm, EcoSharpTM Weed & Grass Killer |
| Acetic Acid+Citric Acid | All Down®, Brush-Weeds & Grass Herbicide |
| Citric Acid | Blackberry & Brush Block |
| Citric Acid + Clove Oil | Burnout® |
| Clove Oil (d-limonene) | Avenger® |
| Clove Oil + Cinnamon Oil | Weed Zap® |
| Clove Leaf Oil | Matran® EC |
| Eugenol | Weed SlayerTM |
| Eugenol + 2-Phenethyl Propionate + Sodium Lauryl Sulfate | EcoSmart® |
| Lemon grass Oil | GreenMatch® EX |
| Ammonium Nonanoate | AXXE® |
| Pelargonic Acid + Fatty Acids | Scythe® |
Resources
- Gaither, Emma. University of Missouri. Use of Acetic Acid for Spring Burndown of Select Annual Weeds. 2019.
- Smith-Fiola, D. And Gill, S. University of Maryland. Vinegar: An Alternative to Glyphosate? Accessed January 18, 2019.
