Waterhemp found in Manitoba

Waterhemp, a bothersome weed for growers in Iowa and Illinois, is now in Manitoba.

The weed was found last fall in a soybean field southeast of Winnipeg. The discovery in the Rural Municipality of Tache may be the first detection of waterhemp in Western Canada.

The finding wasn’t a shock because waterhemp has spread throughout North Dakota, including fields next to the Canadian border.

However, weed experts were surprised to find it in the RM of Tache, more than 70 kilometres from the U.S. border.

“I was really expecting the first reports to come in from right along the border,” said provincial weed specialist Jeanette Gaultier.

It’s not known if the waterhemp is resistant to glyphosate, the active ingredient in Roundup. Gaultier and Rob Gulden, a University of Manitoba weed scientist, sent a sample to a lab for testing.

The discovery in Manitoba is worrisome because herbicide-resistant waterhemp has become a massive headache for soybean growers in the U.S. Midwest.

Iowa State University research has shown that the majority of soybean crops in the state have waterhemp with resistance to herbicides. Five to seven percent of fields have resistance to five groups of herbicides, based on an Iowa Soybean Association report.

Waterhemp, a type of pigweed, arrived in southern North Dakota a few years ago and quickly spread northward.

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“We’re talking about a weed that’s an Illinois weed or an Iowa weed. it seems to be adapting as it goes north,” said Tom Peters, a North Dakota State University weed scientist.

“Weeds have an keen ability to adapt.”

Most of the waterhemp in North Dakota is resistant to glyphosate, and the weed spreads in a predictable pattern.

It appears in a field one year, and the following year there will be a patch of waterhemp.

“Then by the third year, boom, the whole field is waterhemp,” Peters said.

Most of the waterhemp in North Dakota is in the eastern portion of the state, in and around the Red River Valley.

In the short term, Gaultier expects waterhemp will probably be confined to Manitoba’s Red River Valley, but it could spread to other soybean fields in the province.

Gulden said Manitoba soybean growers should be preparing for waterhemp and other new weeds.

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“Soybean isn’t a minor crop anymore. We should be starting to think about some of those weed shifts that come with it,” he said.

“It looks like a lot of those (weeds) could be coming very quickly.”

Peters agreed, adding that farmers in the northern Plains sometimes assume that climate or production practices will prevent the spread of weeds found mostly in the U.S. South and Midwest.

That assumption, he said, is a mistake.

“You can say that we’re different. Well, you’re not really different,” he said.

“I suspect as you see more row crops (in Western Canada) … you’re going to see more of these kinds of weeds appear in your landscape.”

Contact robert.arnason@producer.com

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