Dicamba is a systemic herbicide, a chemical designed to be absorbed by plants and circulated throughout their tissues to kill broadleaf weeds. It has been used in agriculture for decades, but its profile changed dramatically with the introduction of dicamba-tolerant, genetically modified crops, primarily cotton and soybeans, in the mid-2010s. The new seed technology allowed farmers to spray dicamba directly onto their growing crops to manage weeds that had developed resistance to other herbicides, like glyphosate. The controversy stems from the fact that while the engineered crops survive, the herbicide has a distinct and problematic tendency to move far beyond the boundaries of the treated field. This off-target movement has resulted in widespread damage to neighboring farms and natural areas, making dicamba one of the most contentious tools in modern agriculture.
Dicamba’s Mechanism of Off-Target Movement
The core reason dicamba is difficult to control lies in its chemical property known as high volatility. Volatility refers to the herbicide’s tendency to convert from a liquid application into a gas or vapor hours or even days after it is sprayed. This invisible vapor can be carried long distances by the wind, sometimes traveling for miles before settling on non-resistant plants. The symptoms seen across entire fields often point toward this vapor drift as the primary mechanism of injury.
This differs significantly from physical drift, which is the immediate movement of tiny spray droplets by wind during the application itself. Physical drift typically causes injury that is most severe right along the edge of the treated field. Manufacturers attempted to mitigate the volatility issue by creating newer, low-volatility formulations. Despite these efforts, significant off-target injury is still widely reported. Furthermore, the risk of volatilization increases substantially with high temperatures, particularly those above 86 degrees Fahrenheit, which are common during the summer months when the herbicide is applied to growing crops.
Widespread Crop Damage and Economic Fallout
The unavoidable off-target movement of dicamba has caused immense agricultural and financial damage, creating deep friction within farming communities. Millions of acres of commercial crops that are not genetically engineered to resist the herbicide are highly susceptible to even trace amounts of exposure. Non-dicamba-resistant soybeans, which wilt and cup their leaves after exposure, have been the most widely damaged row crop.
Specialty crops that represent significant economic investment are also extremely vulnerable. Crops like grapes, peaches, tomatoes, melons, and various vegetables can suffer severe yield loss or total destruction from dicamba exposure. For example, by late 2017, at least 3.6 million acres of soybeans had been injured, with estimates suggesting that as many as 15 million acres were struck in subsequent years. This widespread destruction often results in “neighbor-to-neighbor damage,” where a farmer using the herbicide legally ends up damaging the crops of a nearby farmer. The economic fallout includes not only reduced yields but also lower crop quality and the substantial costs associated with investigating and remediating the damage.
Ecological Impact on Non-Agricultural Areas
The herbicide’s propensity to move beyond field boundaries extends its damage into natural ecosystems, affecting biodiversity. Native plant species and wild habitats adjacent to agricultural land are just as sensitive to dicamba as non-resistant crops. Trees, including oak, sycamore, and cypress, show distinct symptoms like puckered, cupped leaves and dieback, which can accumulate over years of repeated exposure.
Wild flowering plants, such as common boneset, are particularly susceptible to sub-lethal doses of the herbicide. Exposure can significantly delay the onset of flowering or reduce the total number of flowers produced. These wild flora are the food sources for native pollinators and beneficial insects, including honey bees and syrphid flies. The destruction of these floral resources can lead to a marked decrease in pollinator visitation, threatening the long-term health and stability of local ecosystems.
Legal and Regulatory Challenges
The widespread damage triggered extensive litigation and regulatory action. Farmers who suffered crop losses filed numerous lawsuits, including high-profile class-action cases against the manufacturers of the herbicide and the seed technology. Legal proceedings have resulted in significant financial settlements, such as a $400 million agreement reached by one manufacturer to compensate farmers for past crop losses.
The Environmental Protection Agency (EPA) has repeatedly attempted to mitigate the off-target movement by imposing strict label requirements, such as application cut-off dates, wind speed restrictions, and mandatory specialized training for applicators. Despite these measures, federal courts have twice vacated the EPA’s registration for the use of certain dicamba products on growing crops, most recently in 2024, citing the agency’s failure to adequately address the risk of widespread damage. This cycle of registration, damage, legal challenge, and vacation has created a chaotic and unstable regulatory environment, making long-term planning extremely difficult for farmers relying on the herbicide system.