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Preplant and State Cutoff Dates for Postemergence Applications May Be Dicamba’s Future

It’s expected that EPA will soon be announcing plans for the 2019 label.

Using dicamba as a preplant weed-management tool or abiding by state cutoff dates for postemergence applications may be a way to make dicamba-tolerant soybean systems palatable for 2019.

“My dad used to tell me nothing good happens after midnight,” says Jim Reiss, senior vice president of product development for Precision Laboratories. “With dicamba, nothing good happens after June 20.”

Some good news: At this point, complaints about off-target applications on soybeans are down compared with 2017. Kevin Bradley, University of Missouri Extension weeds specialist, pointed out that as of July 25 last year, 1,411 dicamba-related injury investigations were being conducted by the various state agriculture departments. University weed scientists estimated dicamba had injured approximately 2.5 million acres of soybeans.

As of July 15, 2018, around 600 cases were being investigated by state departments of agriculture. University weed scientists estimated 1.1 million acres of soybeans had been injured by dicamba. Bradley adds, though, that these totals do not reflect states unwilling to participate and provide information for this survey.

“I would also be remiss if I did not mention that these numbers are reflective of what has happened after tighter label restrictions, cutoff dates in certain states, and mandatory training which were not in place in 2017,” he wrote in a University of Missouri press release last month.

Still, Bradley asks if the official dicamba-related injury investigations and/or approximately 1.1 million acres of dicamba-injured soybean constitute a problem for U.S. agriculture. He also asks if all this can be explained by some combination of physical drift, sprayer error, failure to follow guidelines, temperature inversions, generic dicamba usage, contaminated herbicides, and improper sprayer clean out, but not volatility. 

University weed scientists have recommended date and temperature cutoff dates as a way to reduce off-target dicamba movement.

What’s Up for 2019

The EPA registration for dicamba used in dicamba-tolerant systems expires on November 9 this year. It’s expected EPA will soon announce its intent, as farmers are starting to select seed for 2019. Reiss notes that state-specific cutoff dates are a better way to lower off-target dicamba movement than federal rules.

One possibility may be to enact dicamba application zones modeled after soybean maturity zones, with corresponding postemergence cutoff dates.  This builds upon applicator training conducted last winter by universities and industry, he says.  

“Applicators are taking this more seriously,” says Reiss. “Those who didn’t use the right nozzles last year are using them now.”

He says applicators are also more aware of temperature inversions and to avoid spraying in them. “If you can hear a tractor on the next section that you normally don’t hear, that is an inversion. When you smell smoke that you can’t see, that is an inversion.”

 “By far, a large majority (of applicators) followed the label very well in 2018,” says Kevin Cavanaugh, director of research for Beck’s Hybrids. “But we still saw a tremendous amount of drift and volatilization into sensitive crops, whether it was nondicamba soybeans or a neighbor’s garden or some trees.”

That prompted Beck’s Hybrids to write a letter to the EPA to recommend its concerns. “If we don’t control this herbicide, it could reflect very badly on agriculture,” he says. “A second concern is weed resistance.”

As more dicamba-tolerant soybeans are planted – for yield potential, weed control, and as a way to deter damage from off-target dicamba – the more one form of weed control will be used. “Driving the entire farming community to use just one technology is just going to lead us to weed resistance at a very fast rate,” he says.

That prompted Beck’s Hybrids to recommend to the EPA to modify the current label to one for preplant applications or cutoff dates specific to each state.

“Customer reaction has been incredibly positive,” says Cavanaugh. About half of respondents to a farmer-customer survey agreed with either cancelling or changing the dicamba label for 2019. Just 22% said it should not be changed at all.

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