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Research Highlights
Weed Management Considerations for Michigan non-GMO Soybean Growers

Michigan State University Extension hosts an annual weed tour at the agronomy farm, where herbicide programs and weed issues are discussed with farmers. The tour includes the non-GMO soybean plots where specific herbicide programs are applied.

By Carol Brown

Some Michigan farmers are growing specialized soybeans commonly known as non-GMO (genetically modified organisms). Several grain processors in the state have dedicated areas for handling non-GMO soybeans — Zeeland Farm Services (ZFS), Zeeland, Mich., is one of the largest in the United States. These soybeans are mainly exported to markets overseas.

Growing non-GMO soybeans is not much different than producing Roundup Ready varieties, but there are things to consider such as herbicide usage. Christy Sprague, a Michigan State University (MSU) Extension Weed Specialist, has been conducting weed control studies for all crops for many years and specifically researching weed control programs in non-GMO soybeans for more than a decade.

“For Michigan growers, there’s a good market for non-GMO soybeans,” says Sprague. “About 10 percent of the soybeans produced in the state are non-GMO. Because of this, we want to help these growers solve their weed issues, which mainly include herbicide-resistant ragweeds, marestail (horseweed) and several grasses.”

Sprague is studying weed management in these specialty soybeans through a project supported by the Michigan Soybean Committee. She and her research team keep non-GMO soybean plots at the University’s research farm to compare herbicide products and weed control systems.

“Each year MSU Extension hosts a weed tour at our agronomy farm and as part of the tour, we’ll include the non-GMO soybean plots,” says Sprague. “The non-GMO buyers, such as ZFS, invites their growers to the field day, and together we’ll discuss the different herbicide programs, their successes and failures, and issues that growers are experiencing.”

With this continued farmer interaction, Sprague keeps on top of what to study to find solutions to Michigan weed problems. And over the years, she and her colleagues have come up with several recommendations and considerations for non-GMO soybean fields.

“For those starting to grow non-GMO soybeans, we want them to start in their least-weedy fields,” recommends Sprague. “And start with a good pre-emergence herbicide program, one that will provide a good residual, followed by scouting for weed escapes. A post-emergence herbicide plan can then be tailored based on what the weed escapes are.”

Many non-GMO soybean growers are using PPO-inhibitor products such as Flexstar or Cobra to control common ragweed, says Sprague, as ragweed resistant to the ALS-inhibiting herbicides (Group 2) eliminates some available choices.

A key recommendation Sprague asks these soybean growers to keep in mind is herbicide rotation restrictions for future rotational crops (Figure 1).

Figure 1. Consider herbicide rotation and soil pH restrictions in Michigan fields.

“We have a lot of non-GMO growers who rotate to crops that have sensitivity to herbicides,” she says. “For example, if they also grow sugar beets, they need to choose their herbicide programs carefully. Some products have two-year, or even three-year, rotation restrictions. Products like Pursuit would not be usable if sugar beets are in the rotation because of the long-term impact on sugar beet establishment.”

Sprague also recommends these weed management practices for non-GMO soybean growers:

  1. Start with a field as clean of weeds as possible. In some cases, Sprague recommends tillage to control early-season weeds such as marestail. Tillage will bury small weed seeds and reduce chances of a big outbreak.
  2. Know the weeds in your field. It is important to tailor the herbicide program to the weeds present in the field, especially those that are herbicide resistant.
  3. Use a good soil-applied or pre-emergence residual herbicide product to manage weeds that will emerge later.
  4. Stay timely with post-emergence herbicide applications to control weeds after emergence. Make applications when weeds are 2- to 4-inches tall, generally.

Another aspect of Sprague’s research focuses on the economics of weed management plans. Some of the herbicide programs used in non-GMO soybean fields can be more expensive and Sprague’s team does the math for comparisons.

“The key goal of this research is our economic analysis; every year we put together the prices of the herbicide programs and record the yields in the research plots,” Sprague says. “We publish an economic analysis at the end of each season. Even though a lot of money is invested into an herbicide program, the increase in yield usually pays for it, especially with the higher value of the non-GMO soybeans.”

These cost analyses are shared each year with farmers at the weed tour as well as at winter meetings held across the state. The economic analysis includes cost of herbicide programs and application, soybean yield and crop selling price. Fact sheets of this study are available on the MSU Extension website. Information about the annual weed tour and winter meetings can be found on the website as well.

Read about Sprague’s research to control marestail and waterhemp, also funded by Michigan Soybean Committee.

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.