Photo: Lamb's-quarters. © 2020 Delena Norris-Tull
Dicamba (BANVEL) Herbicide
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, October 2020.
Dicamba is a selective herbicide, a Group 4 auxin agonist, thus it causes uncontrolled growth in plants. It has been used for post-emergent control on various broadleaf weeds in corn, soybeans, among other crops. It was first registered for use in the US in 1967. It has been used extensively throughout the United States, and has many trade names as it is used in over 1000 US products.
Dicamba is highly volatile and has caused damage to many non-target crops, through spray or volatilization drift. After the development of dicamba resistant soybeans, and the promise by Monsanto that the latest dicamba formulations would limit its potential for drift, in 2016 the US EPA permitted dicamba to be sprayed “over-the-top,” which means it could be sprayed over the entire soybean field. Despite Monsanto’s claims, spraying over-the-top in soybean fields increased the likelihood of drift onto non-target crops. “In a report dated Nov. 1, 2017, the EPA said it had tallied 2,708 official dicamba-related crop injury investigations (as reported by state departments of agriculture). The agency said there were more than 3.6 million acres of soybeans impacted at that time. Other impacted crops were tomatoes, watermelon, cantaloupe, vineyards, pumpkins, vegetables, tobacco, residential gardens, trees and shrubs.” Ammonium sulfate, often used to enhance herbicide effectiveness, can dramatically increase dicamba volatility (10 things to know about dicamba). Dicamba can persist in the soil longer than glyphosate. By 2018, seven weed species had been found to be resistant to dicamba.
While not considered highly toxic to animals or humans, not enough research has been conducted on its effects (National Pesticide Information Center). It is moderately toxic in humans and other mammals by ingestion, and likely only slightly toxic through absorption through the skin. But it is highly corrosive to the eyes. Dicamba is considered only slightly toxic to birds. While not considered toxic to aquatic invertebrates, dicamba potentially is an endocrine disruptor in fish in colder waters. It is not considered toxic to bees. The US EPA has concluded that it is not likely that it is a human carcinogen, but not enough research has been conducted on this.
In Arkansas, agriculture is the State’s biggest industry and brings in $16 billion to the economy annually. In Arkansas, dicamba had been used extensively to combat pigweed, which invades many crops. Pigweed eventually developed resistance to RoundUp, in use in Arkansas since the 1970s, thus many farmers switched to using dicamba. But many reports of dicamba killing non-target crops led to investigations to determine the extent of unintended crop damage.
In 2017, after the Arkansas Plant Food Association placed a 120-day ban on the use of dicamba, the Arkansas Dicamba Task Force reviewed research and testimony on how far dicamba can be spread by the wind. Monsanto and BASF, the main companies that distribute dicamba, claimed the herbicide will damage crops no more than 110 feet from where it is sprayed. Research by independent scientists claimed that it can damage crops and even trees as far away as 300 feet. The Task Force recommended that farmers not distribute dicamba between April 16 and October 31. This recommendation was approved by the Arkansas State legislative council. Monsanto sued the State to prevent the ban, but an Arkansas judge rejected Monsanto’s suit (Gladden, 2017). In 2017, Arkansas and Missouri banned the use of Dicamba.
In 2018, the US EPA gave dicamba products conditional re-registration for two years, due to concerns about damage to non-target crops. In 2020, the US EPA placed cancellation orders on three of the four dicamba formulations used in the US, which provide highly restrictive circumstances in which the herbicide may be used, with a final use date of July 31, 2020. All four products are classified by the EPA as “Restricted Use Pesticides.”
In some dicamba formulations, the salts are highly soluble in water, and residues have been found in some ground water. Sheley, et al., 2011, reported that “dicamba and picloram are highly mobile in the soil… High application rates, high rainfall following application, or direct application… to water bodies can pose a significant threat to water resources.” They concluded that, “The effect of herbicide on desirable vegetation remains difficult to predict.”
Many lawsuits against Monsanto by various States and farmers, from 2016 to 2020, have recently resulted in Bayer (the company that bought Monsanto) agreeing to pay $400 million in claim settlements to farmers and $250 million in punitive charges.
Within this website, refer to the section Impacts on the Environment & Health, for research summaries on herbicide drift, and the impact of dicamba on native forbs.
References:
The following sections provide information on some of the most widely used modern herbicides:
Next Sections on Herbicides:
Dicamba (BANVEL) Herbicide
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, October 2020.
Dicamba is a selective herbicide, a Group 4 auxin agonist, thus it causes uncontrolled growth in plants. It has been used for post-emergent control on various broadleaf weeds in corn, soybeans, among other crops. It was first registered for use in the US in 1967. It has been used extensively throughout the United States, and has many trade names as it is used in over 1000 US products.
Dicamba is highly volatile and has caused damage to many non-target crops, through spray or volatilization drift. After the development of dicamba resistant soybeans, and the promise by Monsanto that the latest dicamba formulations would limit its potential for drift, in 2016 the US EPA permitted dicamba to be sprayed “over-the-top,” which means it could be sprayed over the entire soybean field. Despite Monsanto’s claims, spraying over-the-top in soybean fields increased the likelihood of drift onto non-target crops. “In a report dated Nov. 1, 2017, the EPA said it had tallied 2,708 official dicamba-related crop injury investigations (as reported by state departments of agriculture). The agency said there were more than 3.6 million acres of soybeans impacted at that time. Other impacted crops were tomatoes, watermelon, cantaloupe, vineyards, pumpkins, vegetables, tobacco, residential gardens, trees and shrubs.” Ammonium sulfate, often used to enhance herbicide effectiveness, can dramatically increase dicamba volatility (10 things to know about dicamba). Dicamba can persist in the soil longer than glyphosate. By 2018, seven weed species had been found to be resistant to dicamba.
While not considered highly toxic to animals or humans, not enough research has been conducted on its effects (National Pesticide Information Center). It is moderately toxic in humans and other mammals by ingestion, and likely only slightly toxic through absorption through the skin. But it is highly corrosive to the eyes. Dicamba is considered only slightly toxic to birds. While not considered toxic to aquatic invertebrates, dicamba potentially is an endocrine disruptor in fish in colder waters. It is not considered toxic to bees. The US EPA has concluded that it is not likely that it is a human carcinogen, but not enough research has been conducted on this.
In Arkansas, agriculture is the State’s biggest industry and brings in $16 billion to the economy annually. In Arkansas, dicamba had been used extensively to combat pigweed, which invades many crops. Pigweed eventually developed resistance to RoundUp, in use in Arkansas since the 1970s, thus many farmers switched to using dicamba. But many reports of dicamba killing non-target crops led to investigations to determine the extent of unintended crop damage.
In 2017, after the Arkansas Plant Food Association placed a 120-day ban on the use of dicamba, the Arkansas Dicamba Task Force reviewed research and testimony on how far dicamba can be spread by the wind. Monsanto and BASF, the main companies that distribute dicamba, claimed the herbicide will damage crops no more than 110 feet from where it is sprayed. Research by independent scientists claimed that it can damage crops and even trees as far away as 300 feet. The Task Force recommended that farmers not distribute dicamba between April 16 and October 31. This recommendation was approved by the Arkansas State legislative council. Monsanto sued the State to prevent the ban, but an Arkansas judge rejected Monsanto’s suit (Gladden, 2017). In 2017, Arkansas and Missouri banned the use of Dicamba.
In 2018, the US EPA gave dicamba products conditional re-registration for two years, due to concerns about damage to non-target crops. In 2020, the US EPA placed cancellation orders on three of the four dicamba formulations used in the US, which provide highly restrictive circumstances in which the herbicide may be used, with a final use date of July 31, 2020. All four products are classified by the EPA as “Restricted Use Pesticides.”
In some dicamba formulations, the salts are highly soluble in water, and residues have been found in some ground water. Sheley, et al., 2011, reported that “dicamba and picloram are highly mobile in the soil… High application rates, high rainfall following application, or direct application… to water bodies can pose a significant threat to water resources.” They concluded that, “The effect of herbicide on desirable vegetation remains difficult to predict.”
Many lawsuits against Monsanto by various States and farmers, from 2016 to 2020, have recently resulted in Bayer (the company that bought Monsanto) agreeing to pay $400 million in claim settlements to farmers and $250 million in punitive charges.
Within this website, refer to the section Impacts on the Environment & Health, for research summaries on herbicide drift, and the impact of dicamba on native forbs.
References:
- Gladden, Alex. (2017). Dicamba & Arkansas Agriculture. Arkansas Money and Politics (AMP). Little Rock, AR. http://amppob.com/dicamba-arkansas-agriculture/
- Sheley, R.L., James, J.J., Rinella, M. J., Blumenthal, D., & DiTomaso, J.M. (2011). Invasive plant management on anticipated conservation benefits: A scientific assessment. In D.D. Briske (Ed.) Conservation benefits of rangeland practices: Assessment, recommendation, and knowledge gaps. (pp. 293-336). USDA Natural Resources Conservation Service.
The following sections provide information on some of the most widely used modern herbicides:
Next Sections on Herbicides: