Why You Should Avoid Applying Dicamba During a Temperature Inversion
Earlier this summer, Perry Galloway needed to spray a soybean field. The Gregory, Arkansas, farmer had success with earlier Engenia applications on dicamba-tolerant soybeans in the Roundup Ready Xtend System, and he planned to use it again. Engenia is a new dicamba formulation that officials for its manufacturer, BASF, say is lower in volatility than previous dicamba formulations.Still, Galloway was cautious about applying Engenia, since reports had swirled in numerous media stories and country coffee shop regarding off-target dicamba movement this summer. This was just before Arkansas issued a 120-day ban on the sale and use of dicamba products on July 11.
To meet label specifics for the field, Galloway needed an eastern wind direction. Engenia’s label states drift potential is lowest between 3 mph and 10 mph, and it prohibits applications above 15 mph.
Since current wind conditions were calm, Galloway delayed the application the following day, when an east wind meeting the label specifications resulted. Calm conditions can cause dicamba – and any other herbicide, for that matter – to become trapped in a temperature inversion. This can cause herbicide to be moved across the road or several miles, depending on where the inversion goes.
“This was in a crucial area,” says Galloway. “I just could not afford to get this (dicamba) on a neighbor,” he says. Because he sprayed at the optimum wind speed while following other parameters, he successfully made the application with no off-target movement.
If you have or are planning to spray dicamba, keep this example in mind. You’ll have to follow all label specifics to prevent off-target movement.
Companies that make the new dicamba formulations for the Roundup Ready Xtend System (Engenia, Monsanto’s Xtendimax, and DuPont’s FeXapan) say the formulations are lower in volatility potential than other dicamba formulations that farmers have used for years, such as Banvel and Clarity.
Still, they can veer off target through factors like temperature inversions if conditions are right. University of Arkansas (U of A) Division of Agriculture researchers have also found volatility differences in field settings between older dicamba products, and the newer ones aren’t as evident as they are in a lab setting. The researchers found that every dicamba formulation they tested in 2017 demonstrated volatility. Some formulations could continue to volatilize at least 36 hours after application and move from the target site in spite of the most label-compliant application efforts.
Formulations tested included Engenia, Xtendimax, and FeXapan. In a U of A news release, Tom Barber, U of A weed scientist, said lab testing found these three new formulations to be less volatile than older formulations like Banvel and Clarity.
“However, when you look at the new formulations in a field setting where volatility measurements are based on soybean injury, differences in volatility between older dicamba products such as Clarity and newer ones including Engenia and Xtendimax are not as evident,” Barber said.
“Although the new formulations are reduced in the amount of volatility that you can see, they’re not zero,” he said. “We don’t know the level of volatility that’s required to injure soybeans. Soybeans are so sensitive, very, very low levels of volatility can cause injury.”
At an agricultural media teleconference BASF held this week, company officials acknowledged off-target dicamba damage has occurred. However, they also pointed out that Engenia has activity on over 200 types of broadleaf weeds, including those hard-to-control weeds that often struggle with resistance like tall waterhemp, giant ragweed, palmer amaranth, and marestail.
Scott Dauk, a Madison Lake, Minnesota, farmer who joined Galloway and BASF officials on the call, said waterhemp had always been a challenge on his and his brother’s farm. He noted that dicamba products like Engenia are giving good control of problem weeds like waterhemp and giant ragweed, provided the right weather conditions occur.
“It seems like other products would burn the weeds back. But after a week or two, weeds would start shooting new shoots out below the dead area and keep growing like nothing happened,” he says.
Keeping It Home
Keeping the herbicide at home and away from neighboring fields will be paramount in 2018. BASF officials said they are collaborating with federal and Arkansas officials to establish recommendations for use in that state. They said BASF will continue to invest in more educational sessions. BASF officials said they have received fewer damage reports in states where applicator training was intensified, such as Alabama, North Carolina, and Georgia.
One way to limit off-target movement is to avoid spraying during temperature inversions. This summer, Tennessee instituted a rule to limit dicamba spraying from 9 a.m. to 4 p.m. in order to reduce the chance of off-target movement due to temperature inversions.
Chad Asmus, BASF technical marketing manager, says spraying during a temperature inversion is prohibited on nearly all pesticide labels. However, he points out, BASF officials are in a discussion with EPA officials on how this can be further clarified.
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