Dicamba (3,6-dichloro-2-methoxybenzoic acid) is a selective systemic herbicide first registered in 1967. Brand names for formulations of this herbicide include Dianat, Banvel, Diablo, Oracle and Vanquish. This chemical compound is a chlorinated derivative of o-anisic acid. It has been described as a "widely used, low-cost, environmentally friendly herbicide that does not persist in soils and shows little or no toxicity to wildlife and humans."

Despite its success in improving crop yields, dicamba has attracted controversy. According to the United States Environmental Protection Agency (EPA), dicamba's primary ecological risk is for non-target terrestrial plants from exposure through spray drift, whereby dicamba inadvertently migrates to non-targeted neighboring areas, damaging those plants.

In 2016, dicamba was approved for use in the United States over GMO dicamba-resistant crops created by Monsanto. Dicamba came under significant scrutiny due to its tendency to spread from treated fields into neighboring fields, causing severe damage. The controversy led to litigation, state bans and additional restrictions over dicamba use.

Dicamba is a selective and systemic herbicide that kills annual and perennial broadleaf weeds. Its primary commercial applications are weed control for grain crops and turf areas. It is also used to control brush and bracken in pastures, as well as controlling legumes and cacti. In combination with a phenoxy herbicide or with other herbicides, dicamba can be used for weed control in range land and other noncrop areas (fence rows, roadways, railways,pipelines, transmission lines and wastage). Dicamba is toxic to conifer species but is in general less toxic to grasses. Dicamba is a synthetic auxin that functions by increasing plant growth rate, leading to senescence and cell death.

The growth regulating properties of dicamba were first discovered by Zimmerman and Hitchcock in 1942. Soon after, Jealott's Hill Experimental Station in England was evaluating dicamba in the field. Dicamba has since been used for household and commercial weed control.

Increasing use of dicamba has been reported with the release of dicamba-resistant genetically modified plants by Monsanto. In October 2016, the EPA launched a criminal investigation into the illegal application of older, drift prone formulations of dicamba onto these new plants. Older formulations have been reported to drift after application and affect other crops not meant to be treated. A less volatile formulation of dicamba made by Monsanto, designed to be less prone to vaporizing and inhibit unintended drift between fields, was approved for use in the United States by the EPA in 2016, and was commercially available in 2017. As a result, the use of dicamba in U.S. agriculture rose sharply from approximately 8,000,000 pounds (3,600,000 kg) in 2016 to 30,000,000 pounds (14,000,000 kg) in 2019, according to the U.S. Geological Survey.

Dicamba came under scrutiny due to its reputation for drifting from treated fields onto neighboring crops. In 2011, the European Food Safety Authority identified dicamba's potential for long-range transport through the atmosphere as a critical area of concern. In 2022, the United States Environmental Protection Agency identified spray drift as the primary ecological risk for dicamba due to its potential effects on non-target terrestrial plants. Dicamba is also available in a drift-resistant formulation, which is less likely to affect neighboring fields.

In 2022 the EPA identified potential occupational risks to handlers mixing and loading dry flowable formulations for application to sod and field crops. The Agency did not identify dietary, residential, aggregate, or post-application risks of concern.