Bloomberg Law
July 1, 2019, 10:31 AM

Rainy Spring May Wash Out Dicamba Pesticide Analysis

Adam Allington
Adam Allington

Record-setting rains that swamped fields and delayed planting across the Midwest this spring may also harm the ability of pesticide regulators to see whether new rules covering the use of dicamba are effective.

Dicamba is a herbicide that controls broadleaf weeds. Crops bio-engineered with dicamba-tolerant traits can then be sprayed without being damaged. But dicamba also has history of drifting into neighboring fields. That’s what happened in 2017 and 2018, resulting in millions of acres of damage to off-target crops in several states.

Partly in response to the drift issue, the Environmental Protection Agency in October 2018 extended the registration for dicamba for a provisional two-year time period, until Dec. 20, 2020, instead of the normal pesticide registration period of 15 years. It also issued new labels requiring mandatory applicator training, and provisions to minimize volatility and drift.

This year—2019—was supposed to be the first big test of whether those new label requirements actually resulted in fewer damage claims. However, farmers and pesticide officials now say the conclusions that can be drawn from this year may be limited.

Record Planting Delays

The problems in assessing the effectiveness of the new rules for dicamba start with delayed crop planting—and thus dicamba application—due to flooding and extreme wet weather. Soybean development is well behind what it would normally be, forcing many farmers to use other herbicides besides dicamba.

The North Dakota Department of Agriculture announced June 26 that it will extend the dicamba application cut-off date for soybeans from June 30 until July 10. Regulators in Illinois also extended the deadline for in-crop use of dicamba until July 15.

Typically, farmers try to wait until crops have matured as much as possible before applying herbicide. If they spray too soon, weeds can have more time to grow back.

Despite the tightened weather-related window, regulators say cutoff dates for applying dicamba remain important.

“While the weather has had an impact on planting this year, which I know is frustrating for many producers, the fact remains that warmer conditions in July increase the risk of volatility and drift when using dicamba products,” South Dakota Secretary of Agriculture Kim Vanneman said in a public statement.

Because of the increased risk of drift when dicamba is applied at higher temperatures, the cutoff date for South Dakota will remain June 30, Vanneman said.

“I encourage producers to explore the other products available to them once the cutoff date for use of dicamba has passed,” she said.

Wait Until Next Year

The three primary companies that make dicamba-based products are BASF SE, Corteva Agriscience, and Bayer AG.

In a statement, Bayer said it had trained more than 30,000 growers and applicators ahead of the season.

“As the season has progressed, we’ve continued to work closely with growers to offer weed management recommendations that factor in the wet weather experienced this season,” Bayer said in its statement. “This season, flexibility is key.”

Companies, regulators, and farmers were all hoping to see whether efforts to minimize off-target damage had been effective.

“But now I’m not so sure 2019 will turn out to be an accurate gauge of whether those changes have been a success,” said Harlan Asmus, the CEO of Asmus Farm Supply, based in Rake, Iowa.

Asmus said many farmers in his region are either being forced to use alternative herbicides, such as glyphosate or 2,4-d, or may not have been able to get a crop planted at all. That could skew the total sample size of farms using dicamba.

“It doesn’t really give us a chance to compare apples to apples,” said Doug Goehring, the Agriculture Commissioner for North Dakota.

“The thing we are really trying to discourage now, because of the shortened time frame, is people may try to go out and spray under less-than-ideal conditions,” he said.

Repeat of Years Past?

In states that grow a lot of soybeans, such as Iowa, Illinois, Minnesota, and Nebraska, state agriculture officials have been bracing for another year of high numbers of damage complaints.

“One of the primary take home messages from the last two years is that its become extremely difficult to keep field staff employed when they get burned out on [the high number of] dicamba investigations,” said Tim Creger, a pesticide program manager with the Nebraska Department of Agriculture.

Speaking at a meeting of state pesticide officials in early June, Creger said it has taken a lot of resources to educate farmers about the new dicamba label requirement and to train replacement staff to oversee investigations into crop damage.

“All four states in our region have had to fall back to a triage system of pesticide investigations,” he said. “This year it’s going to be kind of learn as you go,’ he said.

Watching for Results

New requirements mandate that anyone who applies dicamba must complete a certified applicator training. The rules also include tighter restrictions around variables such as temperature, wind speed, and record-keeping.

While violations are often hard to prove, dicamba-label penalties can include everything from a warning letter, to tens of thousands of dollars in fines.

Others are optimistic that new requirements will make dicamba safer to use. Jeff Bunting is a crop protection manager for Growmark, a Bloomington, Ill.-based cooperative that provides a range of agriculture services, including pesticide application.

“I do think a lot of these new stewardship guidelines will make a difference,” Bunting said.

Unlike previous years, he said more attention is being paid to how things like wind direction, wind speed, and temperature inversions impact drift. An “inversion” occurs when cool air trapped near the ground suspends pesticide particles within it—until the air eventually warms and disperses them.

“All the training, the preparation, the changes to things like buffer zones and the identification of sensitive areas, all these things are getting much more visibility now,” Bunting said.

To contact the reporter on this story: Adam Allington in Washington at

To contact the editors responsible for this story: Gregory Henderson at; Pamela Atkins at; Anna Yukhananov at