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Richard Zollinger, a North Dakota State University weed scientist, speaking at the 20th Wild World of Weeds seminar in Fargo on Jan. 17, 2018, said there are many unanswered questions about dicamba herbicide drift problems in 2017. Photo taken Jan. 17, 2018, in Fargo. (Forum News Service/Agweek/Mikkel Pates)

Zollinger dives into dicamba issue

FARGO, N.D. — "What's the moral of the dicamba story?" asked Rich Zollinger, a North Dakota State University Extension Service weed specialist, delivering his last speech at an event he helped invent — the 20th Wild World of Weeds.

Zollinger, who retired suddenly in December 2017 for family reasons after nearly 30 years at NDSU, talked about his theories of the controversial dicamba herbicide drift problems in his last appearance in leadership in front of about 300 agronomy consultants, farmers and industry specialists.

Off-target dicamba drift was apparent in 2017, leading to visual curling of leaves of soybeans in North Dakota, especially in the southeast part of the state where there are more soybeans and greater concerns over herbicide-resistant weeds. Yield impacts were hard to pin down.

Zollinger described a wild year of politics in which Arkansas regulators grappled with an April 15 application cutoff date. The Arkansas State Plant Board received an anonymous letter of concern from an Arkansas "bench formulation chemist" who feared for his career for commenting about it. The board sent a jet to fetch Zollinger in North Dakota and "personally delivered me to the plant board."

They gave him five minutes to verify the scientist's concerns, he recalled. Arkansas proposed banning dicamba from mid-April to November, drawing lawsuits from manufacturer Monsanto. Some Arkansas farmers rallied at their capitol this week to protest the ban.

In North Dakota, Zollinger looked ahead to 2018 by pointing to the newly-published NDSU Weed Guide. He urged farmers to consider following June 20 as the cutoff — and not the June 30 cutoff on a state label imposed by North Dakota Ag Commissioner Doug Goehring.

"After that, you're more likely to cause serious injury to soybean," Zollinger said.

Still questions

Zollinger said manufacturers have yet to answer numerous "basic science questions" about the "fate" of dicamba under drought conditions, whether dew will dissolve "crystal" deposits on soybean leaves and soil, and how dicamba causes symptoms 30 days after exposure.

Zollinger offered his own theories.

The droplets dry to form crystal residue, which can be dissolved by rain and dew. It can also be "dissociate" from the new, anti-volatile chemistry in the presence of ammonia, which is released naturally from the leaves themselves and from the breakdown of organic matter in soil.

Zollinger pointed to Nebraska research that shows soybeans absorb 38 percent without surfactants (wetting agents) to 75 percent if applied with certain surfactants. Meanwhile, soybean roots "exude 66 percent of all of the absorbed dicamba."

"If a half-pound is applied, a quarter-pound is sitting on leaf surfaces or in the soil," he says, noting that by that math 7.5 million pounds of dicamba is "free" in North Dakota.

Tom Peters, an NDSU and University of Minnesota Extension sugar beet specialist who formerly worked with Monsanto developing herbicide-resistant crop technology, said the industry will have to "sort out the volatility" to keep the technology viable.

Peters said industry science is done "with great integrity" but may need to be more in-depth. The industry's goal is to "get something commercialized," Peters said. But after it's turned loose on millions of acres, "sometimes, as in the case of dicamba, unexpected things occur," he said, adding, "We can't afford to have 20 or 25 percent of our fields with symptomology. That's just unacceptable."

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