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Herbicide-resistant weeds a growing problem

FARGO — A growing problem is creeping up among crops throughout North Dakota and Minnesota.

Some weeds have become resistant to the herbicides used to control them.

In some parts of the country, growers have lost their farms because they didn’t act in time and the weeds got so out of hand, said Rich Zollinger, North Dakota State University Extension Service weed specialist.

The problem isn’t that bad here, but it is a serious issue that’s growing, Zollinger said.

There are numerous confirmed cases in North Dakota and Minnesota of the weeds horseweed, Kochia, common ragweed, giant ragweed and waterhemp showing resistance to glyphosate, the active ingredient in Roundup.

“Those are really tough weeds to kill in our crops,” Zollinger said.

In 2006, there was one confirmed case of glyphosate-resistant giant ragweed in McLeod County, Minn. Last year, there were more than 100 confirmed and highly suspected cases across nearly half of both states, according to weed resistance maps by NDSU Extension Service.

Greg LaPlante of Wahpeton-based GL Crop Consulting has done crop consulting work for 30 years. He said it’s a serious issue, and in the last couple of weeks, he’s seen the herbicide-resistant weeds in fields.

“I hope growers who don’t think it’s a serious problem will heed the warning,” he said.

Ever since glyphosate became widely used in the late 1990s, Zollinger said weed control has been easy. Growers needed only one herbicide, which killed all the weeds instead of going through a weed management program using multiple herbicide control measures.

“Mother Nature always wins,” Zollinger said. “You can try to trick Mother Nature. You can try to pull a fast one, but Mother Nature doesn’t live in a vacuum.”

Zollinger said that when growers spray one herbicide repeatedly every year, sometimes two to four times a year, eventually weeds that can tolerate the herbicide survive and make seed.

“The next year, instead of having one plant, you have 100 and then if you don’t kill those, the next year you have 100,000 and the next year you have 100 million,” he said.

Now, with all of the glyphosate-resistant weed strains, Zollinger said growers will have to return to the practice of managing weeds instead of just killing them. The problem with that, he said, is that while glyphosate doesn’t injure the crop, older herbicides might stunt or yellow it a bit.

“Growers want as much yield as they can without injury,” he said.

Another major issue is the herbicides growers used to apply are a lot more expensive. Glyphosate might cost growers $2.50 to $3 per acre. Other herbicides, Zollinger said, can cost anywhere from $40 to $60 per acre.

Tracy Frank

Tracy Frank is a SheSays, Variety, and Farmer's Forum reporter for The Forum of Fargo-Moorhead. Have a comment to share about a story? Letters to the editor should include author’s name, address and phone number. Generally, letters should be no longer than 250 words. All letters are subject to editing. Send to

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