Weed experts: Keep ag chemicals on the farm

Speakers on Jan. 18, 2022, at the Wild World of Weeds conference at the Fargodome covered a wide range of topics, including the improper use of farm protection chemicals in urban settings and the herbicide resistance of Palmer amaranth.

A North Dakota State University weed specialist and a Corteva marketing specialist speak to an audience at a seminar in the Fargodome on Jan. 1, 2022.
Andrew Thostenson, North Dakota State University Extension pesticide specialist, flanked by Bridgette Readel, Corteva Agriscience, marketing specialist, warned attendees at the Wild World of Weeds seminar in Fargo on Jan. 18, 2022, about the pitfalls of agricultural chemistry finding their way into compost where they could persist to harm horticultural crops. Photo taken Jan. 18, 2022, in Fargo, North Dakoa.
Mikkel Pates / Agweek
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FARGO, North Dakota — Speakers on Jan. 18, 2022, at the Wild World of Weeds conference at the Fargodome covered a wide range of topics, including the improper use of farm protection chemicals in urban settings and the herbicide resistance of Palmer amaranth.

Andrew Thostenson, a North Dakota State University Extension pesticide application specialist, appearing with Bridgette Readel, a marketing development specialist for Corteve Agriscience, talked about the importance of carefully following the label to avoid chemical residues ending up in urban gardens where they could damage plants and impact regulation.

One situation that has made the news has been when locations — including cities — take grass clippings to compost them and then make the compost available to the public for garden and horticultural purposes. Clopyralid (branded as Stinger, Curtail and others) is a selective herbicide used for control of broadleaf weeds, especially thistles and clovers. Manufacturers deregistered it for domestic because of cases in 2000 and 2001 where it didn’t break down with the normal compost heating process.

In 2020, the city of Rapid City, South Dakota, released “several thousand tons of contaminated compost” to the public, Thostenson said. These situations needlessly can raise the ire of state and federal departments of agriculture, and can lead to the U.S. Environmental Protection Agency limiting the use of chemical tools farmers need.

Protect the tools

Thostenson said there are many errant pathways, but if people in cities have weed problems, it’s conceivable that a farmer friend who uses a chemical legally in farm fields may unknowingly incorrectly (and ultimately, illegally) recommend this as a solution in town. The chemical could kill the lawn’s weeds but have an unintended consequences in the compost.


Damage could add regulatory scrutiny to the chemical and reduce its safe use for farmers.

Thostenson said sometimes gardeners can inadvertently spread carryover chemical that comes with straw mats or bundles from construction sites, or from bales that were sold as decorative items or came from construction sites.

“That stuff is garbage, and it ends up in compost,” Thostenson said.

Bridgette Readel, Corteva Agriscience, marketing specialist, said it’s vital to remember that chemicals used in agriculture don’t necessarily translate into being used in lawns and gardens. Users must follow the labels.

“Using a molecule where we are spraying one of our pastures: are we making sure the animals have a correct ‘clean-out’ period, before we move them somewhere so that the manure is clean when we want to use it on a lawn or garden?" Raedel said.

Raedel acknowledged there have been instances where molecules made by her company are suspected of downstream damage, but noted it is not easy to to track the chain of events.

Both said U.S. has only so many chemistry molecules to control weeds and other pests, so agriculturists need to do everything they can to make sure they’re used properly, so there are no unnecessary conflicts with Master Gardeners groups, and others.

Raedel noted that in one case last summer in Fargo, a horticulture talk show received a call from an unnamed individual giving “unsolicited advice” about using an off-label chemical. The horticulture expert host contradicted the caller, and the next day Thostenson followed up with a segment on the station to emphasize the danger.


Good, bad news

On another separate topic, Quincy Law, a North Dakota State University researcher since April 2021, described research on Palmer amaranth seed from a major outbreak relating to sunflower screenings.

Quincy Law, a North Dakota State University weed researcher,  poses in front of a research poster at the Wild World of Weeds seminar in Fargo on Jan. 18, 2022.
Quincy Law is a North Dakota State University assistant professor for research of invasive and noxious weeds. Photo taken Jan. 18, 2022, in Fargo, North Dakota.
Mikkel Pates / Agweek

A 1,000-acre infestation on the Tyler Elston farm in rural Spiritwood, North Dakota, in Barnes County, was discovered in 2020 . Elston had received about 75 semi loads of sunflower seed screenings as feed. The screenings originated from Red River Commodities in Fargo. They were trucked by David Buskohl’s trucking company of Wyndmere, North Dakota. Buskohl had sold the screenings to farmers instead of taking them to be destroyed through incineration at the ADM sunflower plant at Enderlin, North Dakota.

Law, speaking at the weed seminar, said a study of Palmer amaranth weed seeds from the Barnes County control site have now gone through the first of three planned research tests in greenhouses at NDSU.

The tests so far have found that the seeds produced plants that were resistant to five of about eight existing common “chemistry” families used to kill weeds in crops. (The study must be repeated two more times before this summer to be scientifically valid, a process that likely will be complete in the summer of 2022.)

North Dakota State University weed researcher Quincy Law stands in silhouette in front of a slide about Palmer amaranth research at Wild World of Weeds, a seminar in Fargo on Jan. 18, 2022.
Quincy Law,a North Dakota State University weed researcher, speaking in a Wild World of Weeds seminar in Fargo on Jan. 18, 2022, says Palmer amaranth weeds found in sunflower screenings at a large Barnes County site in 2020 were resistant to five major herbicide classes. There are still tools to control them in corn and soybean crops, but at higher cost.
Mikkel Pates / Agweek

On the positive side, Law said the NDSU study verified that aggressive use of chemical tools still can control Palmer amaranth, if applied when growing corn. The study didn’t address costs, but other studies indicated eradication efforts cost double what crop spray costs where Palmer amaranth isn’t present.

Chemical resistance is one of the reasons Palmer amaranth is dangerous for crops. It also outgrows even the tallest corn and produces more than 1 million seeds per plant.

Law acknowledged that — because it’s likely sunflower screenings come from various locations and seed sources in the U.S. — it is impossible to say that an infestation in Barnes County would have seed with the same resistance profile as infestations in another county, even if it resulted from screenings from the same processing plant.

Expensive research efforts by NDSU or others to study the characteristics would have to start over again in another county, because the geographic source of the sunflower seeds that are commingled as screenings is indefinite.


A separate infestation at Shields, North Dakota, in 2021, involved screenings from the CHS Sunflower of Grandin, North Dakota.

While Red River Commodities has described that they are testing loads for Palmer amaranth, there is no scientifically valid protocol for testing loads that could indicate the level sampling provides confidence in the result, and some have suggested it would take dozens of samples per load to provide high confidence in the result.

Mikkel Pates is an agricultural journalist, creating print, online and television stories for Agweek magazine and Agweek TV.
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