Dicamba is a selective herbicide used for post-emergent control of broadleaf weeds in corn, soybeans, and a variety of other food and feed crops in Minnesota. It can also be used for weed control in residential areas. Dicamba is a highly volatile chemical that can damage non-target plant species through spray drift and/or volatilization (vapor drift). Misuse of products containing this active ingredient may cause serious damage to non-dicamba-tolerant (non-DT) soybeans and to other sensitive crop and non-crop plants.
Dicamba is a selective herbicide in the chlorophenoxy family of chemicals. It comes in several salt formulations and an acid formulation. These forms of dicamba have different properties in the environment. Products with dicamba frequently contain other herbicides as well.
Uses/benefits of Dicamba Herbicide
Dicamba (CAS 1918-00-9) is primarily used as an herbicide, frequently with other herbicides. Exposure to dicamba may occur through oral, dermal, or inhalation routes. The mechanism of action of dicamba in mammals is not known, while it is a growth regulator in plants. Dicamba toxicities in humans are primarily acute and include vomiting; bradycardia; shortness of breath; cyanosis; depression; muscular weakness; mild skin, eye, gastrointestinal, and respiratory tract irritation; and death. There is no specific antidote to dicamba toxicity, and the treatment is symptomatic and supportive.
Features of Dicamba Herbicide
1. It’s a broadleaf killer. Dicamba is a selective herbicide in the chlorophenoxy family of chemicals that controls or suppresses only broadleaf plants, but will leave grass weeds and plants alone. This is unlike glyphosate that is nonselective and controls plants regardless of the species. Dicamba also has some residual properties that persist in the soil, while glyphosate is a non-residual. While dicamba has been introduced as a vehicle to combat glyphosate-resistant weeds, Knezevic says there are currently 16 weeds in the U.S. resistant to glyphosate, but there are also seven weeds already showing resistance to dicamba, including kochia.
2. It has a Group 4 mode of action. Dicamba is classified in Group 4, or with synthetic auxins for mode of action. It selectively kills broadleaf plants by overwhelming the natural auxin pathways. It translocates in both the xylem and phloem, with symptoms most obvious in new growth. Glyphosate is a Group 9 mode-of-action herbicide, which inhibits amino acid biosynthesis. Once applied, herbicides in this group translocate to new growth in the xylem and phloem, so the plants stop growing quickly, but often take more than 10 days to die.
3. It’s a restricted-use pesticide. The U.S. Environmental Protection Agency declared new dicamba products as a restricted-use pesticide for 2018, so they are for use only by certified applicators. New label requirements call for application training, record keeping, wind speed limitations for application between 3 and 10 miles per hour, application timing restrictions, and much more. In addition, applicators must complete dicamba and auxin training to use any of the RUP dicamba products.
4. Use the label. Growers should always follow label instructions strictly when applying pesticides of any kind, but with dicamba, this is as important as ever to avoid the potential for off-target injury not only for non-herbicide resistant soybeans, but also sensitive crops like grapes or tomatoes. Getting the rate exactly right with dicamba is especially important.
5. Do not use ammonium sulfate. While AMS is often utilized as a herbicide additive to increase the efficacy of postemergent herbicides, it should never be used with dicamba because it can drastically increase the volatility of the herbicide by up to 20 times.
6. It’s rainfast at four to six hours. Dicamba is considered rainfast, or adequately dried and absorbed by plant tissues so that it will still be effective after rainfall and irrigation at four to six hours. Glyphosate is typically rainfast in an hour. During his presentation, Knezevic reasons that one way to lower volatility issues with dicamba under irrigation might be to irrigate a field with about one-fifth of an inch of precipitation four to six hours after dicamba application. While he admits that he has no data to back up this theory, researchers will most likely test it this summer.
7. Use coarse nozzles. Coarse or ultra-coarse nozzles can help mitigate the volatility and spray drift issues with dicamba products.
8. Apply before the cutoff date. While some states like Missouri are implementing strict calendar cutoff dates, after which dicamba cannot be legally applied, the label states that it cannot be applied to soybeans after R1 growth stage. Know and understand the cutoff date.
9. Consider volatility and vapor. These can be detected up to 96 hours after application. Adding to the volatility issues with using dicamba, researchers found that vapor from the herbicide is the strongest in the first 36 hours; however, it could still be detected up to four days after application. This is the reason why new restrictions on application, new label requirements and more training is being required of applicators of dicamba products.
10. It has high water solubility. Because dicamba is highly soluble in water, it is more likely to leach during extended periods of heavy rainfall, compared to glyphosate, which is water-soluble, but has a high ability to bind to soil particles.
|Pesticide Type||Herbicide (Group 4)|
|Chemical Class||Benzoic Acid|
|Common Trade Names*||XtendiMax, Engenia and FeXapan|
|Registration Status||EPA: Registered since 1967, new product conditionally registered for 2 years in 2018|
Prices of Dicamba Herbicide
$98.95 – $129.95