Reset Weed Control

Conquer Your Soybean Costs - Reset Weed Control

Destroying, not harvesting, weed-infested patches of crops can prevent weeds from going to seed. (Progressive Farmer image by Pamela Smith)

A parade of pigweed occurs far too often from Mike Morgan's fields to a hole near his farm shop in northeast Arkansas.

It's not a joyous event with the Piggott farmer and his employees throwing candy. Instead, pickups and wagons haul recently cut or pulled herbicide-resistant Palmer amaranth to a hole, where the vile pigweed is dried and burned.

Morgan fears if he doesn't spend $100,000 or more annually on chopping crews to physically remove Palmer amaranth from soybeans and other row crops before harvest, his livelihood would be threatened. Herbicides alone no longer provide effective weed control.

"If you don't take care of pigweeds [Palmer amaranth], they will take care of you," Morgan says. "You can see where they have totally taken over farms. We fight pigweed tooth and nail to keep the numbers down so they don't explode."

More than 250 weed species have developed resistance to herbicides, according to the Weed Science Society of America. If left unchecked, weeds may
slice yields by depriving row crops of water, nutrients and sunlight.

Palmer amaranth and waterhemp, both members of the pigweed family, are particularly nasty and tough to control. Each is a prolific weed seed producer known to foil up to seven herbicide sites of action.

Weed scientists urge farmers to adopt a holistic approach to weed control. This includes herbicides, hand weeding, cover crops, weed seed destruction, tillage and more.

Tom Barber, a University of Arkansas Extension weed scientist, says mechanical and cultural weed-control practices may not be cheap and easy, unlike when one pass of glyphosate did the trick. If farmers want to keep weeds at bay and preserve the efficacy of herbicides that still work, he says they need to consider multiple control methods.

"Farmers have to get out of the mentality that herbicides are the only answer," Barber says. "Ever since glyphosate resistance became an issue, we made a huge shift in our education programs to focus on cultural practices to reduce weed numbers. Some farmers don't want to do that because it costs more money, and it's not as easy."


Cover crops such as cereal rye and hairy vetch are Larry Steckel's top nonchemical recommendations to fight herbicide-resistant weeds. Cover crops terminated just before or after planting can reduce Palmer amaranth infestations by 50%, according to the University of Tennessee weed specialist. University of Missouri tests show 50 to 110 pounds of cereal rye planted per acre in the fall and terminated shortly after planting soybeans in the spring can reduce waterhemp stands by 50 to 70% for 28 days after planting.

"That's a huge win," Steckel says. "The weeds that do come up are delayed, which gives farmers more time to get postemergent herbicide applied."

Cover crops outcompete weeds for light, water and nutrients. Terminated cover-crop biomass mitigates weed emergence.

John Lindamood reduced the number of postemergent herbicide applications to control Palmer amaranth on his Tiptonville, Tennessee, farm by planting cover crops on soybean ground.

"The goal is to keep weeds at bay until crops canopy, and then you are home free," he says.


Lisa Behnken, a farmer and University of Minnesota (U of M) Extension crop education specialist, believes the message that weed control can't only come from a jug is getting through.

On average, 30% of 3,200 farmers in Minnesota surveyed by the U of M from 2017 to 2020 admit they pull weeds.

"We're layering herbicides, but here I am still walking fields like I did as a kid," Behnken says. "We have to be creative to outsmart weeds."

She recommends mapping weed escapes to concentrate control efforts the following year. Mowing waterways and ditches is also an effective weed-management tool before harvest. Combines can grab weeds from field or waterway edges, and spread weed seeds. While not desirable, Behnken says mowing down small weed-infested patches of crop may be needed to prevent weeds from going to seed.

"Herbicide resistance is here to stay, but there are control options that can work on different farms," she adds.


Many farmers who were not involved with organic production sold or parked moldboard plows and cultivators decades ago. Circumstances may dictate that producers once again utilize the implements to help control weeds.

Barber says turning soil over to bury weed seeds or ripping weeds out of the ground during the growing season can be effective control measures. He's not suggesting doing this on every acre but certain areas where needed.

"I know deep tillage goes against conservation practices and thinking, but it may be needed, Barber says.

"One weakness pigweed has is seed longevity in the soil is fairly short, like three to five years," he continues. "It won't completely reduce pigweed, but it will cut them down significantly."

For farmers who no longer own a plow or cultivator, there's plenty of used ones on the market. Marzolf Implement Co., in Spring Valley, Minnesota, for example, has several options. Marzolf recently advertised an International 710 five-bottom plow for $750 and a Koen 4RW row-crop cultivator for $1,200.

"You can find them cheap on the used market," says Richard Rohrer, Marzolf parts manager. "People are still pretty stuck on the chemical bandwagon."


The Seed Terminator and the Integrated Harrington Seed Destructor destroy weed seeds at harvest so they can't germinate in the future. Both systems are combine attachments that use hammer mills to pulverize plants, including weeds and weed seeds, following the threshing process.

Weed seed destructors are widely used in Australia. A handful of machines are being tested and used on farms in the United States.

The success rate of the Seed Terminator on destroying waterhemp seed, according to a University of Missouri study, is nearly 99%. Similar findings were found in university tests of the Harrington. However, it takes many years to reduce weed seed banks.

"If you get something that keeps nearly 99% of weed seeds that enter a combine from going back in the soil, it will be very useful," says Kevin Bradley, University of Missouri weed scientist.

> Follow Matthew on Twitter at @progressivwilde.


Past Issues