The University of Missouri has released five key learnings from dicamba research they’ve conducted over the past several years to inform growers using the Xtend soybean and cotton system this season. One study clearly showed that concentrations of dicamba can be detected in the air after on-label applications of approved dicamba products, demonstrating the volatility of these herbicides. Based on these findings, the study shows the need for more focus on determining how much this volatility results in off-target injury and how it can be minimized.

Several weed scientists confirmed through research that adding glyphosate to approved dicamba products will lower the pH of the spray solution. The scientists say this is significant because if the spray tank pH becomes too low, the dicamba could dissociate to its acid form, which is also its most volatile form. Soil pH also has an impact on dicamba volatility. Ongoing research has found that the lower the soil pH, the more volatility there is with the dicamba formulations.

Based on four years of temperature inversion studies, the university confirmed that inversions are common and begin forming prior to sunset, often even earlier than the new dicamba label restrictions, which require applications to end two hours before sunset. When wind is obstructed by tree lines or buildings, studies also showed inversions form more quickly compared to open areas. Cool air masses tend to settle in low points of a field and in some field observations, dicamba injury showed up in the lowest areas. This could indicate that dicamba was applied during an inversion and moved with the cool, stable air mass.

Although dicamba is less likely to move off-target and cause injury when applied as a spring burndown, that doesn’t mean it’s not possible. Last season, the university received more complaints about off-target dicamba movement to specialty crops in April and May than any other time. Research shows there are certain tree fruit, nut and ornamental species that are especially sensitive to off-target movement of this herbicide.

“The University of Missouri research provides important information that can lead to better guidance on the implementation of dicamba-resistant soybean technology in an effort to mitigate the problems that can occur from its use,” said Mark Loux, professor in the Department of Horticulture and Crop Science at The Ohio State University. “It also shows some of the problems with this technology that are out of our control, which really deserved much more attention prior to its release and adoption. However, growers currently have several types of soybean traits and trait combinations to choose from, such as Liberty Link and Enlist, that can be used in situations where the risks of dicamba are too high.”

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