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Dicamba Has Been Around For Years. Why Would It Now Be Causing Problems?

The herbicide dicamba is thought to have been the culprit in more than 3 million acres of damaged soybeans across the country, destroying plants and leaving farmers out millions of dollars in crops.

The chemical has been in use for decades, so why is it today apparently causing farms so much damage?

The answer is two-pronged, according to Kevin Bradley, a University of Missouri assistant professor and weed specialist who has studied the reported damage. Here’s what he says:

Reason 1: Farmers Are Spraying More

In recent years, many farmers used glyphosate -- the active ingredient in the weed killer Roundup produced by agribusiness giant Monsanto -- to destroy pesky weeds like palmer amaranth, or pigweed. About 90 percent of soybean plants, corn and cotton grown in the U.S. are genetically modified to withstand at least one herbicide, so that when farmers spray the fields, the weeds die and the crops survive. Roundup, in particular, grew popular.

Eventually, many pigweed plants grew resistantto formulations of glyphosate. So Monsanto developed soybean seeds genetically modified to withstand new formulations of an older pesticide: dicamba. The seeds entered the market, though, before the new version of the pesticide. Some farmers reached for old dicamba formulations and sprayed their fields. But those versions have been criticized as being too likely to drift in the wind onto neighboring farmland, and onto plants not genetically engineered to withstand the chemicals.

There have always been drift issues with dicamba, Bradley says, but the sheer amount of dicamba sprayed over the past two years has pushed the problems up a notch. He anticipates farmers will continue to spray dicamba to keep pigweed out of the fields in the future, too.

Reason 2: Farmers Are Using Dicamba Later In The Year

Farmers historically sprayed dicamba in April and May around corn and other crops. Today, many farmers are spraying the new formulations of dicamba as late as June and July on the genetically engineered soybean plants introduced in 2016 and on genetically engineered cotton, which was released in 2015.

Spraying later in the year could open up plants to exposure when they are more mature, which could amplify damage.

The U.S. Environmental Protection Agency is reviewing the restrictions it places on the use of dicamba, according to an EPA spokesperson, in light of dicamba-related investigations.

Missouri and Arkansasdicamba sales and use in July. Regulators in Missouri quickly put together a new label with instructions on how to properly prepare and apply the chemical.  Nevertheless, reports of damaged acreage continues to stream in. There are currently more than 2,200 official dicamba-related investigations in the U.S., according to Bradley.

For its part, Monsanto wrote in an open letter to farmers that says, “The overwhelming majority of farmers are experiencing tremendous success during this first year of commercial launch.” The company says it is studying the reports of damage, and that applicator education and trainingis the way to improve accurate application of the dicamba.

The challenge lies in what farmers will do in 2018. As they start making their seed orders in the next few months, it will be interesting to see if more farmers pony up for more expensive dicamba-tolerant seeds in fear of drift damage. 

Copyright 2020 Harvest Public Media. To see more, visit .

As the Midwest Newsroom’s senior content editor, I strive to amplify voices from the region our audiences don’t often hear from. I work with our reporters to seek out stories and experiences that help broaden perspectives and hold people accountable. I also seek to share our team’s reporting in all kinds of mediums to meet our audiences where they are.
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