dicamba

Dicamba is a synthetic plant hormone used as a herbicide to control broadleaf weeds in agriculture and some non-crop areas. Chemically, it is 3,6-dichloro-2-methoxybenzoic acid, a member of the synthetic auxin class of herbicides. Dicamba kills susceptible broadleaf species by mimicking natural plant growth hormones, causing uncontrolled growth, tissue damage, and eventual plant death. Because many grasses are not affected, it is used selectively in fields of crops that are tolerant to dicamba or in non-crop sites after weed emergence.

Dicamba is commonly formulated as esters or salts; ester forms are more prone to volatilization and off-target drift, while certain salt forms are designed to reduce volatility. It is typically applied post-emergence with adjuvants to improve leaf uptake. In many regions, dicamba has been marketed in combination with glyphosate in products designed for dicamba-tolerant crops. Labeling imposes restrictions to manage drift, including guidance on weather, temperature, wind, and droplet size.

Regulatory and environmental concerns have centered on drift injuries to neighboring crops and ornamentals, leading to regulatory scrutiny and various label changes or restrictions in the late 2010s and early 2020s. The emergence of dicamba-resistant weed biotypes in some areas has been reported as a consequence of repeated use. Safety considerations for handlers and applicators emphasize appropriate personal protective equipment and adherence to label directions, while environmental fate generally involves microbial degradation and limited persistence in soil under typical conditions.