Scientist: North Dakota should go for ‘absolute zero’ on Palmer amaranth

Tom Peters, a North Dakota State University and University of Minnesota Extension service specialist focused on controlling weeds in sugarbeets and rotation crops, thinks North Dakota’s response to Palmer amaranth weeds needs to step up to a “zero tolerance” stance, or farmers will face a tripling of weed chemical control costs.

A man in eye glasses stands in a blue suit coat and a "Pro GMO" button, flanked by a trophy case in a university hallway.
Tom Peters, based in Fargo, North Dakota, is an associate professor at North Dakota State University and the University of Minnesota, and is an Extension Service specialist focused on controlling weeds in sugarbeets and rotation crops. Photo taken Oct. 18, 2022, in Fargo, North Dakota
Mikkel Pates / Agweek
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FARGO, N.D. — If North Dakota doesn’t keep Palmer amaranth out now, it will triple costs for weed control for crops like corn and soybeans. Unchecked, it will double the costs for sugarbeets, where costs are already high.

That’s the assessment of Tom Peters, associate professor at North Dakota State University and University of Minnesota Extension Service. Peters works on weed management in sugarbeets and crops grown in sequence with sugarbeets. A typical rotation is sugarbeets, followed by corn, soybean (or dry edible beans), wheat, and back to sugar beets.

Recently three more North Dakota counties — Kidder, Stark and Williams — have had reported outbreaks of Palmer amaranth, bringing the state up to 19 counties where the weed has been discovered and confirmed by the National Agricultural Genotyping Center in Fargo.

Palmer amaranth is a pigweed plant. It is different than the indigenous redroot pigweed and waterhemp that has moved in in the last ten years.

A scientist in a blue sport coat, flanked by trophy cases in a university hallway, gestures with his hands about the seriousness of failing to confront a weed threat.
Tom Peters, an associate professor at North Dakota State University and the University of Minnesota and an Extension Service specialist focused on controlling weeds in sugarbeets and rotation crops, says that if Palmer amaranth takes hold in North Dakota, weed chemical costs would double or triple, depending on the crop. Photo taken Oct. 18, 2022, in Fargo, North Dakota.
Mikkel Pates / Agweek

“Palmer amaranth is a very fast-growing plant. It is competitive with sugarbeets and soybeans,” Peters said.


He explained Palmer amaranth has shown a lot of herbicide resistance, plus the plant produces a "tremendous" amount of seeds that are viable for four to six years.

“Palmer amaranth is going to be a challenge to the longevity of our sugarbeet industry,” Peters said.

NDSU studied weed control costs in Barnes County after a 2020 outbreak related to tainted sunflower screenings. They learned that to control Palmer amaranth in corn, chemical costs would rise from $15 an acre before the outbreak to $45 an acre afterward. Soybean herbicide costs would go from a range of up to $26-$40 an acre before Palmer, to a range of $73-$92 per acre after Palmer. And sugarbeet chemical costs would go from $90 per acre up to a whopping $180 per acre, which would call into question the viability of growing those crops.

Beyond ‘awareness’

Palmer amaranth towers over a row of soybeans just outside of North Platte, Neb., on Tuesday, Aug. 15, 2017. Nick Nelson / Forum News Service
Palmer amaranth towers over a row of soybeans just outside of North Platte, Nebraska, on Tuesday, Aug. 15, 2017.
Nick Nelson / Agweek file photo

For several years now, Extension and others have been on an “an awareness campaign” for Palmer amaranth, Peters said.

“We’ve tried to educate everybody — farmers, cattlemen, landowners, homeowners, everybody — that Palmer amaranth is a plant we don’t want to get established in our landscape.”

The drumbeat has worked in part, he thinks, because “we find Palmer amaranth a few plants at a time” and “most of the time, not finding acres and acres.” He thinks the focus should shift to cattlemen, to understand the consequences of buying screenings embedded with pigweed seeds, including Palmer amaranth.

One source of Palmer infestations has been sunflower screenings, a byproduct of cleaning sunflowers in major processing plants in North Dakota. Processing companies initially built plants to use locally-grown sunflowers. But there are times when demand for their products exceeds supply and they bring in seeds grown in other states that have Palmer amaranth, including South Dakota, Kansas, Oklahoma and west Texas, where Palmer amaranth sometimes is a “pretty common weed.”

There is a regulatory process in North Dakota and good contact between NDSU and the weed control officers. But the state still “isn’t able to prevent it from getting around and into new counties,” Peters said.


“The data speaks for itself. We’re up to 19 counties,” he said. “That’s about 35% of the counties in North Dakota.”

Most of the time, infestations have only been a few plants, Peters said. In one recent case, a county had a place where Palmer amaranth previously had been found, and later "a few hundreds plants" were discovered.

“It’s a little wider infestation,” he said. “Most of the time, we can go out and pull them and get rid of them.”

Pulling the plants “doesn’t set the county back to ‘zero’ because we don’t know how long it’s been there, we don’t know if there’s seed in the soil,” Peters said. “We have to continue to monitor those locations just to ensure that there aren’t new infestation in the following years. It’s people going out and walking the fields.”

Pay now, or later

The bottom line is, Palmer is still spreading,Peters said.

“The number of incidents are increasing,” he said. “What we’re doing isn’t working. We’re not keeping it out. And I think that has to be our goal — we’ve got to find a way to prevent new infestations from occurring.”

Each county has weed control officers, Peters said. One of their jobs is to go out and search for Palmer amaranth — especially in areas where they’ve previously identified it. Peters said he respects the weed control regulatory role, but he said some counties have more resources or manpower than others.

But Peters wonders whether the state should consider a special fund to make sure that if Palmer amaranth is found in a county, there would be funds available to put boots on the ground to deal with it.


“If I was charged with ensuring ‘absolute zero,’ and I had a field I knew there was Palmer amaranth in, I would want to be out there every month during the growing season — May, June, July, August, September,” Peters said.

Palmer amaranth emerges throughout the season, every time there is a rainfall amount.

“Little plants can make seed, too,” he said. “They don’t have to be seven, eight feet tall to make seed.”

Followups need to go at least four years.

Peters acknowledges sunflower screenings aren’t the only source of Palmer amaranth seeds. The seed can into the state in cover crop seed lots or may be a contaminant if someone is buying used equipment that has been in infested fields.

The North Dakota Department of Agriculture in March 2022 held a “Noxious Weed Task Force” meeting last winter in Bismarck, gathering more than 50 commodity groups. Commissioner of Agriculture Doug Goehring presided at the meeting. Peters said he found the discussion to be “productive” but hasn’t heard of any follow-up.

“I think we need to continue the dialog, continue to talk about it, rather than a one-meeting approach to problem-solving,” Peters said.

Peters said Palmer amaranth already is a “prohibitive” noxious weed. That means that if plants are found to be growing they must be eradicated. Planting seed must not contain Palmer amaranth.

But he wonders about tolerances for feed.

“Should you be following the same prohibitive approach (as seed), which is zero?” he said. “There is a very specific, complicated protocol that the industry uses to ensure that there is no foreign matter in feed. Even if you follow that protocol you still aren’t 100% confident. You can only sample so much.”

It’s possible that all sunflower screenings should be destroyed.

Risk to beets

Peters’ thinks the risk of not taking on Palmer amaranth is “tremendous,” especially for sugarbeets and other specialty crops. He noted that the Minnesota Department of Agriculture recently launched a public relations campaign to alert cattle and dairy producers in that state to be wary of obtaining feedstuffs from adjacent  states that have Palmer amaranth infestations, including North Dakota.

Minnesota has long been a dairy powerhouse, but now some of the newer, larger-scale dairies will purchase quantities of feed and then use the manure products locally as nutrients for crops.

“One of the feed sources that they’re buying is screenings,” Peters said. “I understand why they’re buying them, but I think they have to be very concerned or very cautious that the screenings potentially could contain Palmer amaranth seeds. That’s going to make the manure product an undesirable product. It’s going to be hard to get rid of that to neighboring growers, and in many cases those are sugarbeet growers.”

The 2022 crop year was a bad one for weeds, Peters said.

“We planted late. We didn’t get rain to incorporate our herbicides after application,” he said. “The result has been some weed control challenges for our producers, especially waterhemp, but not only waterhemp.”

Palmer amaranth is going to escalate the challenge in sugarbeets even more, he said.

“Unfortunately, we don’t have the technology to control Palmer amaranth if it becomes established in sugarbeets,” he said. “We don’t have the pesticides. We’re flat-out going to beat Palmer amaranth by muscle – by going out and pulling it.”

He said there needs to be a “new weed puller technology” and/or that “new blockbuster pesticide.”

Peters said protecting chemistries that are available now is necessary, as is being more creative about weed management techniques, like tillage, that augment chemicals. Novel technologies — including identifying weeds with cameras and using artificial intelligence — are valid research goals but not viable to help in the next few years.

Specifically, Peters had been optimistic about the promise of a “hooded sprayer” — a nozzle within a hood — to control weeds between the rows, with the hood keeping the spray off of the beets.

“It’s a technical winner,” he said, but is a small-scale approach, compared to current farm field size. Farmers won’t want to “scale back” equipment size, but he predicts they’ll change quickly if they must. 

Palmer amaranth already has a grip in some western U.S. sugarbeet states, like Wyoming, Colorado and western Nebraska. So far, Roundup (glyphosate) is still working on their Palmer to some degree, while Palmer in North Dakota is 100% resistant to glypohosate.

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