Dicamba Briefing

After one season of use, the new formulations of dicamba (Xtendimax, Engenia, and Fexapan) appear to be very effective weed control tools. Our research trials at the University of Tennessee Institute of Agriculture have shown these products to work very well in managing weeds that are resistant to other herbicides. Our Extension specialists and agents have also received anecdotal reports from many farmers who are pleased with the products and say their fields have “never been cleaner.”

Unfortunately, stewarding this technology has proven to be very challenging. Due to the extreme sensitivity of certain crops to dicamba, any level of off-target movement can cause significant symptoms in plants like nontolerant soybeans, tobacco, many fruits and vegetables, and ornamentals.

When applying new formulations of dicamba, producers must strictly follow a long list of directions to keep these products from moving off-target. However, being compliant while also making timely applications can be difficult. For example, when you compare the wind and weather restrictions for the new formulations to weather data recorded at the West Tennessee AgResearch and Education Center, Tennessee farmers only had ninety hours in the entire month of June to safely apply these products.

Additionally, preliminary research results from field studies conducted by Dr. Tom Mueller at the East Tennessee AgResearch and Education Center show that these new formulations—which are marketed as low volatile—still exhibit vapor losses. Whether the off-target movement of 2017 was caused by application error, temperature inversions, volatility, or a combination of factors is still unknown.

So as we move into the harvest season, many questions remain about the future of new dicamba herbicides. Most producers are anxious to see yield data for injured crops. These numbers will help us better understand the ramifications of off-target movement. We are also unsure what, if any, action the Environmental Protection Agency might take in addressing this issue.

I can report that a dicamba working group has been formed to provide input to the Tennessee Department of Agriculture on the use of dicamba technology going forward in Tennessee. The working group will meet later this fall.

I can also say with confidence that UTIA will continue to conduct unbiased research trials of these products and report our findings to Tennessee clientele. We will continue to provide training on best management practices for dicamba use. We will also reach out to farmers and homeowners who have experienced damages from off-target movement by helping them assess potential injury and advising them on mitigation strategies.

Now more than ever, the unbiased research and education provided by public universities and institutes, like UTIA, is needed to navigate this complex issue.