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Controlling pre-harvest Palmer amaranth and waterhemp

Controlling pre-harvest Palmer amaranth and waterhemp

Researchers are testing different methods since herbicides are not an option

By Diego Flammini
Staff Writer

University researchers are looking into how to control weeds prior to soybean harvest.

Prashant Jha, an Iowa State University professor and extension weed specialist, is part of a team studying mechanical options to control Palmer amaranth and waterhemp in soybean fields.

“At this time of year, herbicide applications would be off-label,” he told

Dicamba, for example, cannot be applied after June 30 or up to R1, whichever comes first, the Environmental Protection Agency announced in October 2020.

“We’re looking at other options for farmers and identifying how effective they are,” Jha said.

Jha and his team have been working with three technologies over the last few years.

One is a seed destructor from Redekop Manufacturing out of Saskatchewan, Canada.

The unit can be fully integrated into modern John Deere systems.

Jha’s team used it on a John Deere S680 combine on about 500 acres of soybeans last year and will repeat the tests this year.

The straw still gets distributed out of the back of the combine, while the chaff, which contains most of the weed seeds, is directed into the seed destructor unit.

The unit contains two powerful mills which destroys the seeds.

“It killed about 95 percent of the waterhemp and Palmer amaranth seeds that went through it,” Jha said. “That’s a great result.”

Another system Jha’s team is testing is chaff lining.

The team brought in a chaff lining kit from Westoz Boilermaking Service out of Australia in 2019.

The kit comes with an internal baffle system which gets installed inside the heater and a chaff lining chute. The chute captures the chaff as it exits the rear of the header while still spreading the straw.

“All the chaff and weed seeds are coming through the chute and then we are making a narrow windrow,” Jha said.

“We were reducing the spread of weed seeds by almost 98 percent,” Jha said. “All the seeds were concentrated in that narrow windrow.”

The third way Jha’s team is controlling weed seeds is burning them.

The team will burn some of the weed seeds left in the windrows once and other windrows twice to see the difference in efficacy.

The results Jha’s team have collected are preliminary.

But he wouldn’t be surprised if more farmers adopt these kinds of technologies in the future.

“When you look at the seed destructor, some of the seeds are 1mm in diameter and it’s able to break the seeds,” Jha said. “I think as more data becomes available about these technologies, farmers might look into them as a way to prevent weeds from spreading.”

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