Dicamba Answers

MU Experts Explain Dicamba Damage and Crop Insurance

Missouri farmers listen to MU Weed Scientist Kevin Bradley explain the causes behind the state's many dicamba injury reports this year. (DTN photo by Russ Quinn)

FAIRFAX, Mo. (DTN) -- Dicamba dominated the conversation at the University of Missouri Graves-Chapple Research Center's field day last week.

The annual event is typically devoted to various agronomy research underway at the center, but this year, MU experts spent much of the day discussing the state's problems with off-target dicamba injury.

MU Extension weed scientist Kevin Bradley focused on the reasons behind the injury, from volatility to physical drift and tank contamination, in his talks. MU Extension agricultural economist Ray Massey delved into the insurance issues this herbicide crisis poses to farmers.


Bradley estimates 325,000 acres of non-dicamba tolerant soybeans have been injured by dicamba as of Aug. 17 in the state, with 56 counties out of the state's 114 counties reporting cases. Based on his survey of state weed scientists from the Midwest and South, Bradley estimates dicamba injury has affected 3.1 million acres of soybeans nationwide.

"It is a gross misunderstanding to think this represents the problem," Bradley added. "For every case reported there are probably ten more not reported."

Off-target damage from dicamba can likely be blamed on several different situations, including physical drift, volatility, illegal uses and sprayer contamination, Bradley told attendees of the MU field day.


The new dicamba herbicides -- Monsanto's XtendiMax, BASF's Engenia and DuPont's FeXapan -- limit spraying between wind speeds of 3 to 15 mph, with a 10 mph-limit kicking in under certain circumstances.

Research shows that northwestern Missouri is among the windiest areas of the entire state, Bradley noted.

But while some physical drift is certainly a possibility with the state's dicamba issues this growing season, volatilization is also emerging as a likely culprit, Bradley said.

He estimated that volatilization of dicamba likely accounts for half of the dicamba injury cases he has seen this year.

Research by the University of Missouri and a number of other universities confirms that volatilization is occurring with the new dicamba herbicides, which companies that manufacture the herbicide dispute. "This is where we and the companies part ways concerning this issue," Bradley said.

The new dicamba herbicides are designed to be significantly less volatile than older ones. "But as many have said, less volatile does not mean not volatile," Bradley explained in a recent Mizzou Weed Science article. "All of our results thus far indicate that we can detect dicamba in the air following an application of Engenia or XtendiMax/Fexapan for as many as three or four days following the application. University weed scientists in surrounding states are seeing similar results in their research."

In one Missouri study, after an Engenia and XtendiMax application was made in the field, "indicator" soybean plants were placed in containers in those fields for the first 24 hours following the application and then taken back into the greenhouse for evaluation. Other indicator plants were placed in the field in a similar manner for 24 to 48 hours and 48 to 72 hours after the application.

After seven to 14 days, all of the soybean plants placed back into the greenhouse after the dicamba application showed the distinct symptoms of dicamba injury -- cupping of the leaves.

To help confirm if dicamba was present in the air, researchers us ed air samplers that are able to pull dicamba from the air following application. Dicamba was detected in these filters 72 hours after it was sprayed, Bradley said.

Tank contamination also likely played a role in some of the 2017 dicamba injury reports, Bradley said. "Unfortunately, many have learned the hard way that it takes very, very little dicamba in the tank to cause problems on non-Xtend soybean that are sprayed after a dicamba application," he noted in the Mizzou Weed Science article. "There's no doubt that some portion of our issues with off-target movement of dicamba have been due to improper sprayer cleanout and tank contamination."

The University of Missouri is also doing research on temperature inversions, another likely culprit in the dicamba drift crisis this year.

"As a result of our work on temperature inversions over the past several years, our data indicates that we usually experience a temperature inversion at least one-half to two-thirds of the days in June and July, and that these inversions typically start around 6 to 8 PM and persist for 8 to 10 hours," Bradley explained in the article.

The university is now tracking the occurrence of temperature inversions around the state with this network of weather stations: http://bit.ly/….

See Bradley's Mizzou Weed Science article here: http://bit.ly/….


"We have to get some sort of agreement here on what is causing this," Bradley told field day attendees. "This situation is just killing community relationships."

For 2018, Bradley's official recommendation to soybean producers will be only to spray dicamba as pre-emergence or preplant burndown herbicide, which will limit applications to the spring months. That means growers would not use new dicamba herbicides for post-emergence applications in the summer months of June or July -- when most of Missouri's 2017 injury reports occurred -- or August.

This recommendation will displease some who want to use the product as a post-emerge herbicide to control difficult resistant weeds such as waterhemp and marestail, Bradley acknowledged. But until more definitive research can be done on why dicamba does not stay where it is placed, he believes the risk is too high to spray the herbicide later in the growing season.


MU agricultural economist Ray Massey painted a bleak picture for those seeking an insurance-based solution to lost yield from dicamba injury.

Crop insurance will only pay for a natural loss to a crop. An off-target application of dicamba is not considered a natural loss, Massey explained.

The good news for farmers facing loses from dicamba is the Risk Management Agency (RMA) changed its rules in 2017 to allow growers to exclude years with lower yields from their Actual Production History (APH) under certain conditions. The new rules will allow growers to exclude yields dinged by dicamba from their APH, Massey said.

Your crop insurance agent needs to be notified to investigate a potential loss within 72 hours of you discovering damage, Massey added.

If farmers have soybean losses in just one field and not others, Massey advised them to talk with their insurance agent about the appropriate unit structure to manage APH best. (Units are used in crop insurance to manage a farmer's different crops and fields.)

Massey also discussed the limits to using liability insurance to help recover some losses from off-target dicamba injury.

Liability insurance only covers legal activity. Any applications found to be off-label -- and thus illegal -- would not be covered by liability insurance, Massey said.

The same problem surfaces if an application is deemed "pollutant activities," which often are not covered by liability insurance, Massey added.

Whether the application is classified as accidental or intentional will also affect liability coverage. Companies could argue that those who applied the herbicide should have known this might cause damage and they might not cover these losses as well, he said.

Any confusion or uncertainty over who sprayed the damage-causing dicamba application could also jeopardize liability insurance claims, Massey added. "Insurance companies will fight claims because of this," he said.

So who will pay if crop and liability insurance does not?

Sometimes neighbors can work out damage issues with each other, particularly in smaller cases, Massey said. Beyond that, many neighbors may be unable or unwilling to take responsibility.

In those cases, farmers have only one final resort, civil lawsuits, and should consider contacting an attorney.

Russ Quinn can be reached at russ.quinn@dtn.com. Follow Russ Quinn on Twitter @RussQuinnDTN.

Emily Unglesbee can be reached at emily.unglesbee@dtn.com. Follow Emily Unglesbee on Twitter @Emily_Unglesbee.