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Research Highlights

Research Highlights
Long-term Weed Management Strategies Need to be Considered in Kansas Soybeans

Research plots by Manhattan, KS, which are part of Sarah Lancaster’s layered residual herbicide application study. She and her team are also collecting information on Enlist and LibertyLink G27 soybeans as well as row spacing.

By Carol Brown

Agricultural researchers across the country continue to work on behalf of farmers so they can improve their bottom line while maintaining productivity. Kansas Extension Specialist Sarah Lancaster is one such researcher, who is exploring residual herbicides and row spacing with two soybean varieties.

The Kansas State University Assistant Professor of Agronomy is in the middle of a two-year study funded by Kansas Soybean Commission. She and graduate student Chad Lammers are looking at several herbicide application programs through scenarios with Enlist E3 and LibertyLink G27 soybeans, in 15- and 30-inch rows at three locations across Kansas.

“There are three major aspects of this study that I think are important to look at,” Lancaster says. “First, we have a lot of agronomic information on row spacing, but there are environmental and economic implications that we don’t understand completely.  I also wanted to explore the idea of layered residual herbicide applications. The third factor in this study is collecting data on Enlist and LibertyLink G27 soybeans. There is not a lot of information on these two herbicide-resistant systems in Kansas.”

Figure 1. Palmer amaranth control 4 weeks after treatment in Manhattan, KS. Bars with the same letters are not significantly different.

After the first crop year, she and her research team arrived at preliminary results and found that wider rows yielded higher than narrow rows, but Lancaster chalks this up to limited rainfall and harsher growing conditions than the rest of the Corn Belt. Also, weed control results were similar between the different herbicide plots.

“The results from last year’s research trials showed there were no differences in weed control with or without the layered residual herbicide,” says Lancaster. “We’re not there yet, but we want to tease out the differences between short-term and long-term implications with residual herbicide strategies.”

The layered herbicide protocol Lancaster used includes a control plot, an herbicide application at-planting followed by plots with different post-emergence herbicide applications including:

  • Liberty + Select Max (low management)
  • Liberty + Select Max + Dual Magnum (middle management)
  • Liberty + Select Max + Dual Magnum + hoeing (high management).

The trials were located at Ottawa, Scandia, and Manhattan to capture the three geographic areas of soybean production in the state. All trials were conducted on dryland soybeans.

Lancaster found that Enlist E3 soybeans with medium to high management practices and had better weed controland greater yield than LLGT27 soybeans. Using a layered herbicide practice adds a cost to farmers but Lancaster says that the weed seedbank needs to be considered as they look to more long-term solutions. The added expense of an additional herbicide application may pay off later.

Figure 2. Common waterhemp control 4 weeks after treatment in Ottawa, KS, in 2020. Bars with the same letters are not significantly different.

“We’re collecting this data to analyze the trade-off between the economics in the current year, which may or may not pencil-out in the farmer’s favor,” she says. “We want to know how the long-term implications of herbicide applications effect weed escapes and the herbicide-resistant weed seedbank.”

This year’s harvest is wrapping up and Lancaster will be analyzing yield data and comparing the different fertilizer scenarios to the previous year’s results to get a better understanding of layered herbicide application effectiveness. Lancaster is anticipating her results can help farmers with their long game.

“Farming is tough, and you have to win the battle each year to stay in the war,” she comments. “But you need to have a long-term strategy in addition to your short-term weed management practices.”

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.