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Tom Peters, Fargo, an Extension Service weed specialist at North Dakota State University and the University of Minnesota, guides a Palmer amaranth weed tour of southeast Nebraska in mid-August 2019. (NDSU Extension)

Palmer amaranth tour news mixed

FARGO, N.D. — A North Dakota State University weed specialist in Fargo says there was good and bad news in a recent tour to Nebraska to gauge the threat from Palmer amaranth.

Tom Peters, who holds a joint sugar beet specialist appointment with North Dakota State University and the University of Minnesota, says he has more hope about controlling the infestation, but also is more worried about hay shipments from states that don't label it a noxious weed.

In late August, Peters led a tour to southeast Nebraska, around Holdrege and the North Platte, areas.

Palmer amaranth has been described by some as a "super weed." It's in the pigweed species, related to the more common redroot pigweed and waterhemp that are more common in North Dakota and Minnesota, Peters says.

Palmer amaranth seedsPalmer amaranth has been confirmed in Grant County, as well as McIntosh, Benson, Dickey, Foster and Richland counties in North Dakota. Palmer amaranth was first discovered in Minnesota in 2016. Recently, Lincoln County became the seventh county to confirm it, after Redwood, Jackson, Todd, Douglas, Yellow Medicine and Lyon counties.

Two years ago Peters was "taken aback" by a plant, that can easily get 10 feet tall and 6 feet across. This year tour-goers still saw Palmer amaranth, but also a lot of fields with good control.

Service providers and farmers indicated control is possible with crop rotations, layering multiple herbicides during the year. "We need to pull weeds, we need to use cover crops," Peters said, "but if we put together a system of practices, we can control Palmer amaranth."

Peters studies sugar beets the most, but he frequently talks about controlling weeds across the crop rotation sequence, including soybeans. Sugar beets, as a minor crop, doesn't have some of the tools.

'Deja vu moment'

Sugar beet farmers typically use a pre-emergence herbicide right at planting, and use two applications of soil-applied herbicides in a "lay-by" application — first at the two-leaf stage, and the second at the six- to eight-leaf sugar beet stage. That's before waterhemp and pigweed emerges, but after the beet starts to grow.

Palmer amaranth in NebraskaIn soybeans, however, the Nebraskans were using a similar formula to control Palmer amaranth, but they followed with a final post-emergence application of dicamba or Liberty herbicide.

In Nebraska, farmers will plant soybeans a second year in a row if they felt they weren't adequately controlling Palmer amaranth in soybeans, because they have better control tools with that crop than some others.

They'll follow with corn and a similar weed control program North Dakota and Minnesota growers use.

Dicamba must be applied within 45 days of soybean planting, so farmers must be wary of spraying past that date to stay within the label guidelines.

It's spendy to control Palmer amaranth. The irrigated Nebraska area produces 90-bushel-per acre soybeans yields compared to 45 bushels per acre in non-irrigated North Dakota beans.

"One of the (chemical) retailers said if the farmer wasn't willing to spend $100 an acre (on weed control) he didn't want to get involved," Peters says. To compare, farmers in North Dakota might spend $40 to $50, sometimes $60 an acre for Palmer amaranth control. He says farmers need to use all of the tools, including crop rotation and row spacing and cover crops to keep it at bay.

There was one new worry from the tour.

Peters this time saw "a lot" of Palmer amaranth in alfalfa. This could be a problem because Nebraska designates weeds noxious only if they originate outside of the U.S. Palmer amaranth originated in Arizona and New Mexico.

Nebraska alfalfa farmers are on a 35-day "cut cycle" for alfalfa hay. This allows Palmer amaranth to germinate, emerge and produce viable seed heads before farmers cut it again. "If they're baling that and sending it to producers in other states, that could be a potential way to introduce Palmer amaranth," Peters said. Similarly, Palmer amaranth is not on South Dakota's noxious weed list. It is on the lists in North Dakota, Minnesota and Iowa.