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Is palmer amaranth waiting in the wings?

Experts weigh in on palmer amaranth, its climbing stats to the south, and the chance we might see the weed cropping up in Manitoba

Palmer amaranth.

Provincial weed specialist Tammy Jones says it’s not time to push the panic button on palmer amaranth, despite new cases reported in North Dakota.

Manitoba has cast a closer eye to the situation now that the noxious weed has been spotted in the neighbouring state.

“We knew it was in South Dakota, so the expectation of it moving into North Dakota makes sense,” Jones said.

The weed may eventually spread north, she said, urging farmers to figure out what is in their field, regardless of if those species include palmer amaranth. At the same time, she said, the weed is low on her priorities compared to weeds that are already present in the province.

“As long as they’re vigilant about controlling it in the States, and they seem to be really on top of it there, then it’s likely that it’s going to take a little bit of time before it gets here,” Jones said.

Described as “the No. 1 weed problem in the U.S.” by North Dakota State University, palmer amaranth has had a devastating impact on yield in warmer states. Native to the desert conditions in the southern U.S., the weed has been making its way north, and losses have been reported up to 79 per cent of corn and 93 per cent of soybean yield, according to an NDSU release.

Brian Jenks, weed scientist with NDSU, says he would expect similar damage in cereals or canola.

“It can do just as much damage in those fields because of how fast they grow and how much space they take up,” he said. “Some plants grow vertically and don’t take up a lot of space, but then there’s other plants that branch significantly and could be several feet wide in diameter.”

Seed production is also prolific. Palmer amaranth’s trademark seed heads, which drape snakelike from the crown of the plant, can produce in excess of a million seeds, while the plant itself can grow six to eight feet high, shooting up by two to three inches a day.

Rob Gulden of the University of Manitoba’s Weed Ecology and Management Lab says it’s not clear if Manitoba would also see that devastating growth, given a shorter, colder growing season.

“I’m not sure that we know enough about the biology yet, about how the move to the more northern states really affects it,” he said.

Jenks, however, suspects that the climate won’t significantly hinder the plant given is own observations in the field.

He has plucked plants in North Dakota that were six feet tall or more, he said.

“I’m sure it won’t grow quite as fast up here, but it can grow just as tall,” Jenks said. “It can grow very tall here.”

North Dakota first confirmed palmer amaranth in late August, after a producer in McIntosh County along the North Dakota and South Dakota border noticed a suspicious-looking plant.

The state has since confirmed more cases, not all of them along the southern border, Jenks said. Cases are largely in the eastern part of the state, he said, although the weed has since been noted farther north.

“Right now, we’re focusing mostly on just trying to prevent seed production,” Jenks said. “Trying to get the plants pulled before they set seed and then this winter we plan to talk to them about how to control it next year.”

Some producers are considering fall herbicide to eliminate any undetected plants, although extension staff warn against relying entirely on chemistry.

The weed is infamous for resistance risk. Jenks says samples have been taken for resistance testing, although the weeds have not set seed to test. North Dakota State University strongly suspects plants are already glyphosate resistant, and Jenks is planning greenhouse trials to better grasp the scope of resistance.

The weed’s germination adds another hurdle for management, agronomists in plagued areas have noted. Unlike weeds that germinate early season, palmer amaranth may germinate at any point in the year.

North Dakota State University suspects that many of its confirmed cases so far are late-germinating plants.

Farmers can do little to prevent the weed’s spread into Canada if seeds cross over through flooding or migrating birds. Experts, however, are urging farmers to cast a closer eye to their machinery. All machinery should be thoroughly cleaned if it is purchased and transported across the border, Gulden said, while North Dakota researchers have said custom combine work or other machinery travel might also be vectors for the weed.

“When an invasion comes or when it moves in, it doesn’t move in wholesale,” Gulden said. “It moves in accidentally on one farm or two farms. The early detection we have to leave up to farmers and agronomists because they’re the eyes on the ground and if they see a different plant or plant species, we need to be made aware of it.”

Jones says Manitoba Agriculture has already added palmer amaranth to its weed control and education efforts.

About the author


Alexis Stockford

Alexis Stockford is a journalist and photographer with the Manitoba Co-operator. She previously reported with the Morden Times and was news editor of  campus newspaper, The Omega, at Thompson Rivers University in Kamloops, BC. She grew up on a mixed farm near Miami, Man.



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