GOSHEN COUNTY, Wyo. – It’s a scenario that’s played out too many times in the past year for
A neighbor applies herbicide to a stand of corn and, in the coming days, a soybean field withers and dies. An investigation into the cause points to dicamba, a popular broadleaf herbicide now under fire in agriculture regions across the country.
The problem has become so widespread the U.S. Environmental Protection Agency is considering imposing strict limitations on when dicamba can be applied, possibly going into affect as early as the first half of next year.
Dicamba can be found as an active ingredient in numerous products. It’s used in everything from common lawn care weed killers to the chemicals used to control invasive, noxious weed species in Goshen County and beyond. And it’s a popular applicant for weed control in corn acres across eastern Wyoming and western Nebraska.
“It’s a common herbicide used here,” said Caleb Carter, agriculture educator with the Goshen County office of the University of Wyoming Extension Service in Torrington, Wyo.
“But we’re not having the issues other people are seeing around the country,” Carter said. “It’s a really effective herbicide when it’s used correctly.
“I’d say very few of the farmers who’ve had drift problems were not applying against label directions,” he said. “I’d say 95 percent of them were applying it properly.”
The biggest problems are occurring in areas of heavy soybean production. Monsanto, one company that produces herbicides containing the controversial chemical, also markets a dicamba-resistant variety of soybeans. Many of the problems are coming to light when one producer, who’s using the new variety, sprays upwind from a neighbor who isn’t using the resistant bean variety.
Dicamba-based herbicides are also marketed under different brand names by DuPont, BASF and other world-wide agriculture chemical companies.
Until this past year, when the resistant variety hit the market, dicamba was primarily used only early in the growing season before susceptible plants were emerged and vulnerable, said Andrew R. Kniss, Ph.D., a weed management specialist with the Department of Plant Sciences at the University of Wyoming in Laramie. Dicamba is highly volatile and as the ambient temperature warms, particularly later in the growing season, it’s more likely to aerosolize and drift onto neighboring fields.
Some studies have shown dicamba can convert and move off the field where it was sprayed as long as 72 hours following application, Carter said.
“It’s much more likely to move off site when the temperature is warm,” Kniss said. “High temperatures make it more likely we’re going to see dicamba moving around.
“Where we’d usually apply dicamba in corn, say, in Iowa, the soybeans probably aren’t going to be emerged or very large yet,” he said. “It really wasn’t an issue (before last year), even if there was a little bit of off-site movement, there weren’t as many things around
While widely used in this area, particularly on corn, Kniss and Carter don’t foresee any coming FDA limits on dicamba use having too much of a detrimental effect on growers in this area. While sugarbeets and dry edible beans are susceptible to damage from dicamba exposure, neither crop is as sensitive to exposure as non-resistant soybean varieties. And it’s typically used in this part of the country very early in the season, well before the volatility becomes an issue of concern to neighboring crops, they said.
How, then, did the problems arise in areas of the Midwest and Mid-South?
“That’s the $64,000 question – probably more than $64,000,” Kniss said. “I don’t think we really know all the details.
“My guess would be it’s a combination of many factors,” he said. “The biggest of which is it’s being used at a different time of year, in different weather patterns and in different geographies, that it hasn’t been used in before.”
As far as a full-out ban on the chemical is concerned, Kniss and Carter don’t see that coming down the pipe any time in the foreseeable future. But imposition of a cut-off date on usage in spring or early summer could protect those vulnerable crops during the pre-emergent phase of the growth cycle.
“One hope in the world of weed science is the EPA will leave any restrictions up to the state, even to the county level, to allow safe use of the product and not take it off the shelf all together,” Carter said. “Time will tell.”