Comparison of dicamba spray drift and volatility in post-emergent corn and soybean

Spray drift and volatilization of the herbicide dicamba from agricultural uses is an area of significant study in recent years. While only the low-volatility formulations of dicamba have been approved for use in the United States in post-emergent dicamba tolerant (DT) cotton ( Gossypium hirsutum L.) and soybean [ Glycine max (L.) Merr.], a variety of other dicamba products that are not specifically low-volatility have been approved for decades and can be used as pre-emergent herbicides in certain crops, including soybean and cotton, and in early post-emergent corn applications. This study compared the volatility and spray drift deposition resulting from an approved use of dicamba on DT soybean, an approved dicamba use on corn ( Zea mays L.), and an example of an unapproved use of dicamba on soybean all side-by-side in two locations. Results showed that the downwind spray drift deposition of dicamba was highest in the approved corn applications at both field locations due to medium droplet size and higher release height. The volatility of dicamba during the first sampling interval after application as measured by air concentrations was between 13 and 74 times higher for approved corn or unapproved soybean treatments at 1.5 m above the crop, compared to approved soybean at both study locations. Results from this study suggest that the low-volatility formulations and label measures in DT soybean and cotton uses are beneficial in keeping dicamba off-target movement potential relatively low.