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ND tour group gets up-close look at destructive weed Palmer amaranth

Matt Larson, operations manager at CHS Agri Services Center in Holdrege, Neb., shows a field of soybeans inundated with Palmer amaranth on Wednesday, Aug. 16, 2017. Nick Nelson / Forum News Service1 / 9
Soybeans grow in a zero-weed tolerance field near Minden, Neb., on Wednesday, Aug. 16, 2017. Nick Nelson / Forum News Service2 / 9
A weed resistance tour guest walks through a soybean field filled with Palmer amaranth plants near Holdrege, Neb., on Wednesday, Aug. 16, 2017. Nick Nelson / Forum News Service3 / 9
Jody Saathoff is a farmer and CHS farm representative in Minden, Neb. Nick Nelson / Forum News Service4 / 9
Palmer amaranth plants sway in the breeze near Holdrege, Neb., on Wednesday, Aug. 16, 2017. Nick Nelson / Forum News Service5 / 9
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North Dakota NRCS agronomist Roberto Luciano examines a Palmer amaranth plant on Wednesday, Aug. 16, 2017 near Holdrege, Neb. Nick Nelson / Forum News Service7 / 9
NDSU extension agronomist Tom Peters speaks with guests of the Nebraska weed tour on Monday, Aug. 14, 2017 in North Platte, Neb. Peters was one of the committee members who helped organize the tour to North Platte and the surrounding area to study resistant weeds such as Palmer amaranth. Nick Nelson / Forum News Service8 / 9
Matt Larson, operations manager at CHS Agri Services Center in Holdrege, Neb., speaks to weed resistance tour guests about Palmer amaranth on Wednesday, Aug. 16, 2017. Nick Nelson / Forum News Service9 / 9

HOLDREGE, Neb. — The three dozen agriculturalists peered through the bus windows to get their first good look at what they'd come from North Dakota to see: A field infested with Palmer amaranth, the weeds — replete with seeds — towering triumphantly over the outmatched soybean plants beneath them.

The agriculturalists, many of them seeing the weed in person for the first time, responded with shock and dismay. Their distress grew when tour guide Mat Larson, of Holdrege, a Nebraska-based CHS agronomist, told them that the producer who farmed the land had gone all out, spending heavily on pesticides, to control the weeds.

"I'd thought I'd seen it all, but this tops it all. We were book-smart about this weed, but you can't really grasp how bad it is until you see it for yourself," Tom Peters, the North Dakota State University extension official who organized the trip, said later.

The two-day trip in Nebraska, on Aug. 15-16, was funded by the North Dakota Soybean Council. It sought to educate tour members, most of them NDSU extension officials, about Palmer amaranth, a destructive weed that's well-established in Nebraska and steadily moving north into Agweek Country.

The weed — which has caused yield losses of up to 91 percent in corn and 79 percent in soybeans — already has been found in southern Minnesota and parts of South Dakota. Experts believe it's just a matter of time before Palmer amaranth is found in North Dakota, Montana and the rest of Minnesota and South Dakota, too.

Bill Nielsen, a Minden, Neb., farmer who showed some of his fields to the North Dakota group, knows the threat firsthand.

"This weed can just explode on you," he said.

Because each Palmer amaranth plant has as many as a million seeds, the weed can multiply rapidly, overrunning a field within three to five years from when the first plant begins growing there.

Jody Saathoff, farm representative with CHS in Minden, Neb., who led the North Dakota group through a tour of infested weeds in his area, provided this math:

If a million seeds from one Palmer amaranth plant is spread evenly over 160 acres and 90 percent of those seeds are controlled, there would be 622 plants per acre.

"That's a train wreck waiting to happen," Saathoff said.

Nielsen's approach to Palmer amaranth is "zero tolerance." He tries to eliminate the weed in his fields — an impossible goal, but one that gives him the best chance of moderating the weed's spread. His effort includes walking through the fields and pulling out Palmer amaranth plants by hand.

The corn-soybean rotation, common in much of the Upper Midwest, is dominant in Nebraska, which can help Palmer amaranth get established in a field.

Palmer amaranth is largely hidden from view by corn during most of the growing season. As a result, farmers may not do enough to combat the weed in their corn fields — worsening the problem the following year, when Palmer amaranth is more visible in much-shorter soybeans. By then, however, the weed already may be established.

Why it's so bad

Palmer amaranth is dangerous for many reasons, most notably:

• A single plant can plant as many as 1 million tiny seeds. Because they're so small, they're relatively easy for farmers to spread unintentionally.

• The weed can grow so large that it damages farm equipment, especially during harvest During the tour, Brad Brummond, Walsh County extension agent, held a large, but not fully mature, Palmer amaranth plant and said, "Look at that stem! It's as big as my wrist."

• The seeds are unusually competitive with most crops, including corn and soybeans. What's more, the seeds can lie dormant in the soil for years, waiting to germinate until growing conditions are favorable.

• The weed can grow as much as 3 inches per day, reaching a height of 10 feet or more. The bigger they get, the harder they are to control.

• It closely resembles pigweed and waterhemp, especially when small, so farmers may misidentify it and take inadequate steps to control it. Identification becomes even harder because waterhemp and Palmer amaranth plants interbreed to create hybrids, Saathoff said.

• The weed quickly builds resistance to pesticide.

From a scientific viewpoint, Palmer amaranth is "an amazing plant," albeit one that can badly hurt crops, said Greg Kruger, weed science and application technology specialist at the University Of Nebraska-Lincoln's North Platte Research Station.

The two-day tour included demonstrations at the research station's Pesticide Application Technology Laboratory, which Kruger directs. A separate article in this week's issue of Agweek looks at the still-in-the-early-stages efforts to establish a similar lab on the NDSU campus in Fargo.

What the future holds

Some farmers assume, or least hope, that researchers will develop new pesticides to control Palmer amaranth. But that's a dangerous and unwarranted assumption, according to Peters and other experts.

"Don't expect industry to provide a solution," Peters said.

Experts say the fight against Palmer amaranth will require many tools and tactics — possibly even a fundamental change in how farmers approach their planting decisions.

Now, farmers pick the crop they want to grow in a field, then identify weeds associated with that crop and, finally, select pesticides that combat those weeds. Crop, weeds, pesticide, in that order, with crop the starting point.

In the future, farmers may need to begin with the type of weeds found in a field, then identify pesticides that effectively combat those weeds and, finally, select a crop that's tolerant to those pesticides. Weeds, pesticide, crop, in that order, with weeds the starting point.

Tour participants will take what they learned in Nebraska and develop educational material for agriculturalists in North Dakota. Work to do so began while they were still in Nebraska.

"We need to be as prepared as possible to deal with this weed. It really is a game-changer," Peters said.

Trip takeaways

Three dozen agriculturalists, most of them North Dakota extension officials, visited Nebraska on Aug. 15-16 to learn more about Palmer amaranth, a destructive weed that's working its way north. Here's some of what they learned:

• Pesticides should be applied both before and after Palmer amaranth emerges from the soil in the spring.

• Pesticides alone aren't sufficient.

• So-called alternative tactics, such as narrow row spaces to help growing crops compete, need to be considered.

• Longer rotations — growing two or more crops — allows farmers to use different types of herbicides, slowing the weed's ability to build resistance to it.

• Wheat, which has fallen out of favor with many Upper Midwest farmers because they typically make less money from it, has a role in fighting Palmer amaranth. It emerges relatively early in the growing season, giving it a competitive edge against the weed.

• "Zero tolerance" should be the weed control goal.

• The weed seedbank will take on increased prominence. It's the reserve of viable weed seeds on the soil surface and scattered in the soil. It consists of both new weed seeds and older seeds that have been in the soil for several years

"Managing the weed seedbank will need to be a priority," said Dave Nicolai, University of Minnesota extension crop educator and coordinator of its Institute for Ag Professionals. He was a member of the group that toured Nebraska.

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