Soybean School: Slowing the spread of waterhemp and Palmer amaranth


More and more cases of waterhemp are being discovered, and last year, Manitoba saw its first confirmed finding of Palmer amaranth. As many producers are painfully aware — both weeds can be extra difficult to control, and herbicide resistance has only increased.

Manitoba’s neighbour to the south is no stranger to either weed, with the spread of waterhemp in North Dakota dating back 30 years.

So, what can we do to slow the spread?

Joe Ikley, extension weed specialist at North Dakota State University (NDSU), says late summer/early fall is the best scouting time for the pests.

“It’s what I call pigweed ID season. That’s when not a day goes by that I don’t get a sample [with the question] is this Palmer? Is this waterhemp?” he explains. “This is the time to really pay attention to those escapes. If you have a few plants, don’t run it through the combine is the easiest way to prevent local spread within the field.”

The best starting point to slowing the spread, says Ikley, is getting your pre-emergence or pre-seed herbicides down, as both Palmer amaranth and waterhemp are a lot more difficult to control once they’re out of the ground.

“If you talk with people further south in the U.S. who have dealt with waterhemp and palmer amaranth for 30 years as their main annual weed, the best success is never letting that seed germinate, emerge, or get out of the ground,” he says. “Once it’s out of the ground, once we’re over three inches tall, it becomes a lot more difficult to control. And some chemistries — once we’re four or five inches tall — it actually becomes basically impossible to kill with a certain chemistry…and that’s not very tall.”

Check out the full conversation between Ikley, and RealAgriculture’s Kelvin Heppner, at the Big Iron Farm Show at Fargo, North Dakota, below:

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