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Published July 18, 2014, 02:22 PM

Herbicide-resistant weeds a growing problem for farmers

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, says Rich Zollinger, North Dakota State University Extension Service weed specialist.

By: Tracy Frank, Forum News Service

FARGO, N.D. — 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, says 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 says.

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 says.

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 says it’s a serious issue, and in the past 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 says.

Ever since glyphosate became widely used in the late 1990s, Zollinger says 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 says. “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 says 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 says.

Now, with all of the glyphosate-resistant weed strains, Zollinger says 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 says.

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 says, can cost anywhere from $40 to $60 per acre.

At the high end, that means a farmer with 1,000 acres would have a 1,900 percent increase in weed management costs, jumping from $3,000 to $60,000.

Those costs, Zollinger says, are not being passed along to consumers. Instead, growers are taking it as a loss.

With profit margins already tight, LaPlante says it’s not a loss they can afford.

“The biggest problem is the temptation with narrow margins of crop production now,” he says. “Guys may think they need to cut back on expenses, and then they get themselves into trouble because they can’t control the weeds because they got too conservative on the weed control program.”

Herbicide programs, he says, are the worst expense to cut back on in the next few years. Growers have done more with weed control this year than last year, he said, but even more will need to be done next year, especially with soybean acres.

“We’re at the point of zero tolerance for weeds,” he says.

Sometimes growers will spray and think the weeds have been killed, but if they don’t go back and scout for weeds, it can become a bigger problem, Zollinger says.

“Scouting is a commandment,” he says.

Some growers are taking the issue of herbicide-resistant weeds seriously, but when a grower doesn’t address the problem, LaPlante says it not only affects his field, but his neighbors’ fields as well, often traveling through waterways.

“If growers collectively as a whole don’t get everybody on the same wagon, it may very well end up as a serious problem like in the South,” Zollinger says.

In the Southern part of the country, a weed called Palmer amaranth has become glyphosate-resistant and has taken over entire farms, Zollinger says.

“That one weed is worse than all five of our bad weeds,” he says.

It adapts quickly, competes aggressively with corps, and can produce anywhere from 100,000 to 500,000 seeds, according to Purdue University Extension Service in Indiana, where Palmer amaranth has been confirmed.

“It’s not too far away,” LaPlante says. “If that gets up into our waterways here, we’re all going to have a real serious problem.”

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