Invasive Palmer amaranth threatens crops

Wisconsin State Farmer


Conservation Corps crew members blowtorch palmar amaranth plants. The state hopes to reduce the seeds that might again sprout the fast-growing noxious weed in the spring.

Linda Huff's minivan is filled with garbage bags stuffed with Palmer amaranth she dug up this fall from 20 acres planted with prairie grasses and flowers near Jefferson.

It took the 77-year-old about 15 hours to remove the plants, which can quickly grow up to seven feet tall. She carefully placed flags where she removed each plant, knowing seeds from the highly invasive weed could easily sprout again next spring, moving from field to field, crowding out corn, soybeans and other cash crops.

Farmers in Iowa, Minnesota and some other Midwestern states have learned that the native grasses and prairies planted to help butterflies and other pollinators inadvertently have spread the noxious weed. It has overrun and choked fields across the southern United States, where it has proved resistant to several herbicides, including widely used glyphosate.

"It's a huge threat to agriculture," said Steven Bortz, Huff's son.

Minnesota farm leaders are so concerned about the aggressive, prolific weed that they attacked it with blow torches last fall, seeking to destroy seeds that can reach up to 500,000 on each plant. The weed is in 30 fields, filter strips and plantings in two counties.

Palmer amaranth, which can dramatically cut crop yields, has been identified in 49 counties in Iowa, nearly 10 times as many counties than at the start of the year, said Robert Hartzler, an Iowa State University professor of agronomy.

"We have so much Palmer amaranth in the state, there's no doubt it will establish and move," Hartzler said. "It will have a significant economic impact."

At its worst, Palmer amaranth can reduce soybean yield 80 percent, and corn about 90 percent, studies have shown.

Iowa State experts and agronomists across the state have been sounding an alarm about the weed's widespread introduction in Iowa. But Hartzler and others say the federal government has been mostly silent.

It's still not alerted Iowa farmland owners with up to 200,000 acres in pollinator conservation programs about the weed.

Minnesota's battle

Minnesota placed Palmer amaranth on the state's noxious weed list in 2014, and this year listed it as a prohibited weed seed.

"That helped us get some boots on the ground," said Anthony Cortilet, a noxious weed coordinator at the Minnesota Department of Agriculture.

Since Palmer amaranth was discovered in just two counties, Minnesota contracted with the state Conservation Corps last fall to use propane blowtorches to spot-kill the weed seed.

Wrapped head to toe in flame-resistant gear, the specialized crew burned Palmer amaranth plants in five plantings that hadn't been mowed to the ground yet. They're hoping to reduce the number of new Palmer amaranth weeds that pop up next spring.

"We want to eradicate the weed, not just control it," said Cortilet, whose team is putting together plans to beat back the weed next spring. They, too, want to use herbicides to spot-kill Palmer in conservation reserve fields.

The weed isn't resistant to glyphosate in Minnesota or Iowa conservation plantings.

"...We're giving it the best try we can because we know we have a limited window of opportunity," said Cortilet, adding that the state provided about $50,000 to battle the weed.

The state continues to investigate, but it believes the seed is tied to one pollinator seed mix, he said.


The weed, found in conservation reserve plantings in Minnesota and Iowa, can spread quickly, reducing yields in corn and soybeans.
Minnesota is taking aggressive steps to eradicate Palmer amaranth, tapping a Conservation Corps crew to blow-torch Palmer amaranth plants last fall. The northern state hopes to reduce the seeds that might again sprout the fast-growing noxious weed in the spring. The weed, found in conservation reserve plantings in Iowa and Minnesota, can spread quickly, reducing yields in corn and soybeans.

Burning the plant signals to farmers the importance of stopping the weed, Cortilet said.

He said the state needs farmers to climb "on board" to fight Palmer, he said. "They will be the biggest help — in identifying the plant and learning what works and what doesn't."

Tough to combat

U.S. agriculture agencies are working with Iowa State University, the state and other agencies to determine what actions landowners can take on conservation fields.

Owners of Midwestern land where the weed has been introduced through conservation seed mixes have run into complications trying to control it.

While Hartzler's testing isn't conclusive, he was able to kill Palmer amaranth grown from conservation field seeds with glyphosate, the active ingredient in Roundup, the world's mostly widely used herbicide.

That gives Iowa an advantage over southern states, where the weed is resistant to several herbicides, including glyphosate.

Even if Palmer amaranth can be killed with herbicides in Iowa, it can't be wiped out when the fast-growing plant reaches a certain height, making it extremely hard to control.

And using glyphosate would kill more than Palmer amaranth in native prairie fields, planted with sunflower, coneflowers and other forbs that help feed Monarch butterflies, bees and other pollinators whose populations are threatened by dramatically reduced forage.

"These prairie plants are slow to establish, so the big concern is that the Palmer will thrive while the perennials get established," Hartzler said.

Once the prairie flowers are established, they're expected to crowd out the weed, he said.

Frequent mowing could suppress Palmer amaranth, if landowners actively manage the conservation plantings.

U.S. farmland owners get paid to take cropland out of production under the federal Conservation Reserve Program. Pollinator programs encourage farmers to plant flowers and grasses that will attract bees, butterflies and other pollinators that support $25 billion in fruits, vegetables and other ag production. Landowners get annual rental payments, and are paid part of the cost to plant pollinator mixes and manage the fields.

Tom Vilsack, the U.S. agriculture secretary, called the accidental introduction of Palmer amaranth in conservation seed mixes an "isolated incident."

"There are issues that crop up from time to time, and we're going to adjust and deal with them," Vilsack said.

Bill Northey, Iowa's secretary of agriculture, wants the state to put Palmer amaranth on its noxious seed and weed lists.

The seed designation is designed to prevent noxious seed from entering the state, and the weed law could give farmers, landowners and others more tools to fight its spread.

But the state ag secretary said he's unsure that declaring Palmer amaranth a noxious seed and weed when it first arrived in the state in 2013, likely in livestock feed, would have protected Iowa.

"It's not like the seed would have not been in the mix if it was put on the list," said Northey, adding that officials are still trying to determine how the Palmer amaranth seed got into Iowa's conservation mix.

Some farmers have reported the seed tags indicated there was no weed seed in the pollinator habitat mix.

"It's certainly important to take a stand and say, 'We don't want that here, and you're in violation of our seed laws,'" Northey said. "But is that preventative or is it just something you're able to challenge legally afterward."

Northey, like Bortz and others, believes the added costs farmers and landowners run into fighting Palmer amaranth could spark a rash of lawsuits. "I have a feeling there are lawsuits brewing," Bortz said.