Weeding out resistant weeds the old-fashioned way

If hand roguing a commercial farm field in Manitoba seems like an outlandish investment of your time, you might reconsider after seeing Ingrid Kristjanson’s photos from North Dakota.

Judging from the astonished whistles by some in the St. Jean Farm Days audience earlier this month, the farmers in attendance were inspired, to say the least, to at least give the thought some consideration.

Kristjanson, Morris-based farm production adviser with Manitoba Agriculture Food and Rural Initiatives had photographed fields infested with resistant weed species in Manitoba’s next-door neighbour to the south.

One was of a North Dakota soybean field in Richland County so choked with glyphosate-resistant kochia it resembled a small forest.

The weeds were so dense and tall, she and colleague Jeff Stachler, North Dakota State University/University of Minnesota sugar beet weed specialist, had to be careful not to get lost in it.

“You could easily lose sight of each other in this field,” she said, adding that the overwhelmed farmer had tried to plow it, then decided to wait for a killing frost.

Her point? Keep a watchful eye out for weeds your herbicides aren’t killing, and be prepared to get in there and hand pull any survivors.

Kristjanson went south last fall to learn more about multiple resistance issues developing in North Dakota and Minnesota. She told her St. Jean Farm Days audience of some scary scenarios that could be headed our way.

These include the spread of water hemp resistant to glyphosate (Group 9), water hemp resistant to Group 2, Group 9 and Group 14, and kochia resistant to glyphosate and fluroxypyr.

Found in North Dakota, there is even a suspected, though not yet confirmed case of kochia resistant to fluroxypyr, 2,4-D, glyphosate and dicamba.

Water hemp, a member of the pigweed family, has been found historically in Manitoba. But it’s only a matter of time before the resistant type arrives. It is growing along the Cheyenne and Red rivers and can easily travel by flood waters, said Kristjanson.

Water hemp also produces mind-boggling amounts of seed and can go from one to over six million plants in a single acre in two growing seasons — if the earliest plants aren’t detected and yanked to prevent more selection for resistance.

Given the impact resistance can have, it just makes sense now to get out and deal with these weeds when their numbers are small, Kristjanson said.

“Scouting is going to be key,” she said. “If you can deal with one plant, why not take the time, if you see a few stragglers, to hand weed?” she said.

“It’s the cheapest thing you can do and one of the most effective. If it’s not dropping seeds, there’s no opportunity for the resistance to spread from that plant.”

Other strategies farms have include frequently rotating crops and herbicides.

Managing to prevent resistance

South of the border, in parts of North Dakota, Kristjanson said it was notable to see only the occasional field of wheat or edible beans amidst vast acres of herbicide-tolerant varieties of soybeans, corn and sugar beets.

“One thing we do have going for us in Manitoba is we still tend to have quite a number of crops in our rotations,” she said.

“Having those mixes in there, and growing wheat, winter wheat, oats, sunflower canola… that’s all in our favour. Keeping that broad variety is certainly helping.”

Other management strategies farmers have include choosing the most effective herbicides, rotating herbicide mechanisms of action, applying at the appropriate droplet size and reducing sprayer travel speeds.

It’s key that spraying be done early, stressed Kristjanson.

“I think we get into the trap of thinking to wait until everything emerges,” she said.

“Spray early and spray twice if you need to, but go after those weeds when they are small, when you’ll have a better chance of having good control.”


The old adage of “an ounce of prevention” is especially critical given no “pound of cure” is expected any time soon.

No novel new herbicides are expected in the next five to 10 years, so it’s important farmers manage so they retain the weed control they have, said Kristjanson.

“Glyphosate is the most effective herbicide ever discovered,” she said. “Let’s make sure that we’re preserving it for the future.”

About the author


Lorraine Stevenson

Lorraine Stevenson is a reporter and photographer for the Manitoba Co-operator with 25 years experience writing news and features. She was previously a reporter with the Farmers Independent Weekly and has also written for community newspapers in Winnipeg and Manitoba's Interlake.



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