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Palmer Plagues CRP Acres

Palmer amaranth turned this CRP heaven into the stuff of nightmares.

Fear of being labeled a “poor operator” and difficulty in renting new ground are just two reasons why Palmer amaranth infestations are sensitive topics. To get a better idea of how Palmer amaranth infestations spurred by contaminated conservation planting seed impacted farmers, we contacted several for this story. One agreed to speak, but only if we agreed not to name him. Here is his story.

A 120-acre piece of land in Crawford County, Iowa, seemed like conservation heaven when one farm family enrolled it in a 10-year CRP in 2016. Previously, the ground was no-till in a corn-soybean rotation. Now, it sports conservation perks including a waterway, switchgrass, food plots for wildlife, and a pollinator plot. A hired conservationist planted most of the ground to a mix of seven different grasses the second week in May.  

Due to a shortage of locally grown seed, the custom seeder purchased additional seed from outside Iowa. Unknown to the farmer and custom seeder, this seed was contaminated with Palmer amaranth seed.

Weed Management to Maintain the Planting

The CRP planting was slow to germinate and establish. Meanwhile, the farmer was battling no-till ground with a weed seed bank of ragweed, foxtail, marestail, sunflower, and velvetleaf.  

He mowed a couple times, as his contract allowed. It helped him manage the CRP seeding and not cause an eyesore for his neighbors.

As summer progressed, he started to hear rumblings that Palmer had been found in his county.

He mowed again on August 14 and paid close attention to his field. Prairie grasses and flowers were starting to grow to heights of 2 feet tall, but weeds from the soil seed bank were growing, too.

As summer continued, he started noticing unusual weeds he hadn’t seen for years, like quackgrass, lambsquarter, pigweed, and woolly cupgrass. Concerned about Palmer amaranth, he went to an Iowa State University Extension meeting to learn more about the weed.

“One way to identify Palmer is to compare the length of the petiole and the leaf,” he says.

He walked his field the following day and saw a suspect plant with a longer petiole than the leaf blade, which is a sign of Palmer. Unsure, he sent a photo to his Extension specialist, who positively identified it as Palmer.

The Palmer looked considerably different than what he expected, because it had been mowed off two to three times throughout the season.

“It started bushing out,” he says. “Instead of being 6 feet tall, it started a seed head at 2 feet and was branching out on the ground.” Total eradication was the only option for his operation. “The way I know to control Palmer is to pull and bag the plants and not allow any to go to seed.”

Tree shears were necessary to cut down the Palmer plants, as regular corn knives couldn’t cut the thick 2- to 3-inch stalks. In the end, he cut the Palmer stalks at ground level and placed the plants into plastic lawn bags. There was a total of 250 Palmer plants from the 8-acre pollinator planting where the contaminated seed originated.

He wasn’t done, though. The drill wasn’t completely cleaned out before switching from the pollinator seed to the remaining CRP planting. While scouting the remaining acres in a golf cart, he spotted and cut 50 stray Palmer plants.

“I’m fairly confident I found all of the Palmer because I went out and walked the field every week,” he says. By October, he had 20+ bags full of Palmer. He left them in the bags and planned to burn them in December once the plants started rotting. He cut off the top of an old fuel barrel and mounted it on fence posts. He started by burning wood and then added the bags of Palmer. When all of the bags were completely burned, he used a 50,000-Btu propane torch to kill any seeds in the ashes.


“Mowing Palmer plants isn’t going to stop reproduction, because it can grow laterally and produce seed on the ground,” he says. He informed neighbors that Palmer amaranth was in his fields.

He says he was fortunate because he did his own mowing. All machinery stayed on the farm, which reduced the risk of Palmer spreading.

“The only way to prevent this in the long run would’ve been to not have put it in the government program,” he says. “I couldn’t identify the seed in the prairie seed mix. The only way I was able to distinguish this from the other similar plants in the field was the longer petiole, leaf shape, and longer female seed head that had sharp bracts to the touch.”

Looking forward

“In 2017, my plan is to walk the field with a hand wand with 2,4-D and spray plants that look like waterhemp or Palmer,” he says.

If you are considering signing CRP contracts, he advises that you find local seed free of Palmer amaranth. Meanwhile, read your CRP contracts closely so you’ll know your control options if a Palmer amaranth infestation occurs.

“I’m lucky,” he says. “I started controlling it the first year. For farmers who didn’t, Palmer will have a head start because of the amount of seed that was produced from last year.”

He foresees future issues with absentee landlords who enroll in CRP and have a tenant managing the ground.

"Custom work is going to distribute the seed faster than if you are farming your own ground and doing your own work. Long term, renting out the farm in 10 years would probably be a challenge if I hadn’t controlled Palmer the first or second year. We all have to start controlling Palmer from now on,” he says.

Zero tolerance

Last September, Marc Knupp terminated a 3½-acre pollinator plot that was seeded earlier that spring on his Washington, Iowa, farm. The reason? Palmer amaranth had infested similar pollinator plot seed mixes in his county.  

“I had been interested in doing something conservation oriented with that 3½ acres,” he says. “There was a bunch of things I could not do with it, but the pollinator plot fit perfectly.”

All went well with the paperwork and seeding phase. Matters went off the rails, though, when Palmer amaranth started surfacing in similar pollinator plots in his county.

Knupp and other pollinator plot enrollees had bought the seed mix from a Wisconsin firm. “We looked over my plot two different times, and didn’t find any,” says Knupp.

Still, the findings alarmed Knupp enough that he bought out his contract. Between that and crop revenue loss, this cost between $3,000 and $4,000. He then terminated his plot with glyphosate and 2,4-D.

“Palmer isn’t anything you want to take lightly,” he says. “At worst, it can take 90% of your corn yield and 70% of your bean yield if you don’t do anything. I felt terminating the contract was a price I was willing to pay.”

Placing Palmer amaranth on the noxious weed list in Iowa would help ensure that seed mixes for conservation practices like pollinator plots are Palmer-free, he says. At press time, Minnesota, Ohio, and Delaware are the only states that have declared Palmer amaranth a noxious weed.

“Everyone needs to practice due diligence,” he says.

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