Dicamba is an important herbicide for controlling post-emergent resistant weeds in soybean farming. Quantitative assessment of the off-target transport of field applied herbicides such as dicamba requires focused study design, careful sampling logistics, robust analytical methods, and sophisticated modeling techniques.  These requirements are particularly critical for studies that aim to experimentally resolve the mechanism of off target movement (e.g., differentiate spray drift from volatilization).<br/>This presentation will focus the analytical component of this multidisciplinary approach used to characterize dicamba off target movement.  The analytical phase was supported by the development and validation of two liquid chromatography tandem mass spectrometry (LC-MS/MS) methods that determine the mass of dicamba on either filter paper or polyurethane foam (PUF) air samplers to characterize the off-target mass loss via spray drift or volatilization, respectively.  In addition, liquid chromatography-ultraviolet (LC-UV) methods were used to verify application rates in tank mixtures and in application area filter papers.  The results of inter-laboratory and intra-laboratory method validations that assessed method performance characteristics including dynamic range, accuracy, precision, selectivity, and capability of dilution will be presented along with multi-year, multi-laboratory characterization of long-term performance of the methods through on-going quality controls in good laboratory practice (GLP) studies.  In addition, examples of field designs that differentiate transport mechanisms and logistics for field sample collection that minimize the potential for sample cross-contamination will be presented.

Long-term analytical performance of methods to quantify dicamba off-target movement

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